U.S. patent application number 10/555855 was filed with the patent office on 2006-11-02 for thermoelectric semiconductor material, thermoelectric semiconductor element therefrom, thermoelectric module including thermoelectric semiconductor element and process for producing these.
This patent application is currently assigned to ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD.. Invention is credited to Kouiti Fujita, Isao Imai, Ujihiro Nishiike, Toshinori Ota, Tsuyoshi Tosho, Hiroki Yoshizawa.
Application Number | 20060243314 10/555855 |
Document ID | / |
Family ID | 33432109 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060243314 |
Kind Code |
A1 |
Ota; Toshinori ; et
al. |
November 2, 2006 |
Thermoelectric semiconductor material, thermoelectric semiconductor
element therefrom, thermoelectric module including thermoelectric
semiconductor element and process for producing these
Abstract
A metal mixture is prepared, in which an excess amount of Te is
added to a (Bi--Sb).sub.2Te.sub.3 based composition. After melting
the metal mixture, the molten metal is solidified on a surface of a
cooling roll of which the circumferential velocity is no higher
than 5 m/sec, so as to have a thickness of no less than 30 .mu.m.
Thus, a plate shaped raw thermoelectric semiconductor materials 10
are manufactured, in which Te rich phases are microscopically
dispersed in complex compound semiconductor phases, and extending
directions of C face of most of crystal grains are uniformly
oriented. The raw thermoelectric semiconductor materials 10 are
layered in the direction of the plate thickness. And the layered
body is solidified and formed to form a compact 12. After that, the
compact 12 is plastically deformed in such a manner that a shear
force is applied in a uniaxial direction that is approximately
parallel to the main layering direction of the raw thermoelectric
semiconductor materials 10. As a result, a thermoelectric
semiconductor 17 having crystal orientation in which extending
direction of C face and the don of c-axis of the hexagonal
structure are approximately aligned. As a result, the crystalline
orientation is improved, and the thermoelectric Figure-of-Merit is
increased.
Inventors: |
Ota; Toshinori; (Tokyo,
JP) ; Yoshizawa; Hiroki; (Funabashi-shi, JP) ;
Fujita; Kouiti; (Miura-shi, JP) ; Imai; Isao;
(Fujisawa-shi, JP) ; Tosho; Tsuyoshi;
(Noboribetsu-shi, JP) ; Nishiike; Ujihiro;
(Tokushima-shi, JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
US
|
Assignee: |
ISHIKAWAJIMA-HARIMA HEAVY
INDUSTRIES CO., LTD.
Tokyo
JP
|
Family ID: |
33432109 |
Appl. No.: |
10/555855 |
Filed: |
May 7, 2004 |
PCT Filed: |
May 7, 2004 |
PCT NO: |
PCT/JP04/06493 |
371 Date: |
November 7, 2005 |
Current U.S.
Class: |
136/200 |
Current CPC
Class: |
H01L 35/16 20130101;
H01L 35/34 20130101; B22D 11/0611 20130101 |
Class at
Publication: |
136/200 |
International
Class: |
H01L 35/00 20060101
H01L035/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2003 |
JP |
2003-130618 |
Claims
1. A thermoelectric semiconductor material produced by: layering
and packing plate shaped raw thermoelectric semiconductor materials
made of a raw alloy having a predetermined composition of a
thermoelectric semiconductor to form a layered body; solidifying
and forming the layered body to form a compact; applying pressure
to the compact in a uniaxial direction that is perpendicular or
nearly perpendicular to a main layering direction of the raw
thermoelectric semiconductor materials; and thereby applying a
shear force in a axial direction that is approximately parallel to
the main layering direction of the raw thermoelectric semiconductor
materials; and plastically deforming the compact.
2. A thermoelectric semiconductor material having a compound phase
comprising: complex compound semiconductor phase having a
predetermined stoichiometric composition of a compound
thermoelectric semiconductor, and a Te rich phase in which excess
Te is added to the stoichiometric composition.
3. A thermoelectric semiconductor material produced by: adding
excess Te to a predetermined stoichiometric composition of a
compound thermoelectric semiconductor to form a raw alloy; layering
and packing plate shaped raw thermoelectric semiconductor materials
made of the raw alloy to form a layered body; solidifying and
forming the layered body to form a compact; applying pressure to
the compact in an axial direction perpendicular or nearly
perpendicular to a main layering direction of the raw
thermoelectric semiconductor materials; and thereby applying shear
force in an axial direction approximately parallel to the main
layering direction of the raw thermoelectric semiconductor
materials; and plastically deforming the compact.
4. The thermoelectric semiconductor material according to claim 2,
wherein the stoichiometric composition of the compound
thermoelectric semiconductor is a (Bi--Sb).sub.2Te.sub.3 based
composition.
5. The thermoelectric semiconductor material according to claim 3,
wherein the stoichiometric composition of the compound
thermoelectric semiconductor is a (Bi--Sb).sub.2Te.sub.3 based
composition.
6. The thermoelectric semiconductor material according to claim 2,
wherein the stoichiometric composition of the compound
thermoelectric semiconductor is a Bi.sub.2(Te--Se).sub.3 based
composition.
7. The thermoelectric semiconductor material according to claim 3,
wherein the stoichiometric composition of the compound
thermoelectric semiconductor is a Bi.sub.2(Te--Se).sub.3 based
composition.
8. A thermoelectric semiconductor element produced by: layering and
packing plate shaped raw thermoelectric semiconductor materials
made of a raw alloy having a predetermined composition of a
thermoelectric semiconductor to form a layered body; solidifying
and forming the layered body to form a compact; applying pressure
to the compact in an axial direction perpendicular or approximately
perpendicular to a main layering direction of the raw
thermoelectric semiconductor materials; and thereby applying shear
force in an axial direction approximately parallel to the main
layering direction of the raw thermoelectric semiconductor
materials; and plastically deforming the compact to form a
thermoelectric semiconductor material; cutting out a thermoelectric
semiconductor element from the thermoelectric semiconductor
material so that a plane approximately perpendicular to the
uniaxial direction in which the shear force is applied during the
plastic deformation of the compact can be used as a contact surface
with an electrode.
9. The thermoelectric semiconductor element according to claim 8
wherein the plate shaped raw thermoelectric semiconductor material
have a compound phase comprising: a complex compound semiconductor
phase having a predetermined stoichiometric composition of a
compound thermoelectric semiconductor; and a Te rich phase
including excess Te in the stoichiometric composition.
10. The thermoelectric semiconductor element according to claim 9,
wherein the stoichiometric composition of the compound
thermoelectric semiconductor is a (Bi--Sb).sub.2Te.sub.3 based
composition.
11. The thermoelectric semiconductor element according to claim 9,
wherein the stoichiometric composition of the compound
thermoelectric semiconductor is a Bi.sub.2(Te--Se).sub.3 based
composition.
12. A thermoelectric module comprising a PN element pair produced
by: layering and packing respectively plate shaped raw
thermoelectric semiconductor materials made of a raw alloy
comprising a composition of P type thermoelectric semiconductor,
and plate shaped raw thermoelectric semiconductor materials made of
a raw alloy comprising a composition of N type thermoelectric
semiconductor to form layered bodies; solidifying and forming the
layered bodies to form compacts; applying pressure to the compacts
having the compositions of P type and N type thermoelectric
semiconductor in an axial direction perpendicular or approximately
perpendicular to a main layering direction of the raw
thermoelectric semiconductor materials; and thereby applying shear
force in an axial direction approximately parallel to the main
layer direction of the raw thermoelectric semiconductor materials;
and plastically deforming the compacts to form P type and N type
thermoelectric semiconductor materials; cutting out P type and N
type thermoelectric semiconductor elements from the P type and N
type thermoelectric semiconductor materials so that planes
approximately perpendicular to the uniaxial direction in which the
shear force is applied during the plastic deformation of the
compacts can be used as contact surfaces with an electrode;
arranging the P type and N type thermoelectric semiconductor
elements so that the elements are aligned in the direction
perpendicular to the axial direction of pressure application during
plastic deformation of the compacts, and also perpendicular to the
direction of shear force by the pressure application; joining the P
type and N type elements via a metal electrode.
13. The thermoelectric module according to claim 12, wherein the
plate shaped P type and N type raw thermoelectric semiconductor
materials respectively have a compound phase comprising: complex
compound semiconductor phase having a predetermined stoichiometric
composition of a compound thermoelectric semiconductor; and a Te
rich phase in which excess Te is added to the stoichiometric
composition.
14. The thermoelectric module according to claim 13, wherein the
stoichiometric composition of the P type compound thermoelectric
semiconductor is a (Bi--Sb).sub.2Te.sub.3 based composition.
15. A thermoelectric module according to claim 13, wherein the
stoichiometric composition of the N type compound thermoelectric
semiconductor is a Bi.sub.2(Te--Se).sub.3 based composition.
16. A manufacturing method for a thermoelectric semiconductor
material comprising: melting a raw alloy having a predetermined
composition of a thermoelectric semiconductor; having the raw alloy
to be contacted with a surface of a cooling member to form plate
shaped raw thermoelectric semiconductor materials; layering and
packing the plate shaped raw thermoelectric semiconductor materials
to form a layered body; solidifying and forming the layered body to
form a compact; applying pressure to the compact in one of two
axial directions which are crossing each other in a plane
approximately perpendicular to the main layering direction of the
raw thermoelectric semiconductor materials, while preventing
deformation of the compact in the other axial direction; and
thereby applying shear force in an axial direction approximately
parallel to the main layering direction of the raw thermoelectric
semiconductor materials; and plastically deforming the compact to
form a thermoelectric semiconductor material.
17. The manufacturing method for a thermoelectric semiconductor
material according to claim 16, wherein the raw alloy has a
composition in which excess Te is added to a predetermined
stoichiometric composition of a compound thermoelectric
semiconductor.
18. The manufacturing method for a thermoelectric semiconductor
material according to claim 17, wherein the raw alloy comprises a
composition in which 0.1 to 5% of excess Te is added to the
stoichiometric composition of a compound thermoelectric
semiconductor comprising 7 to 10 atomic % of Bi, 30 to 33 atomic %
of Sb, and 60 atomic % of Te.
19. The manufacturing method for a thermoelectric semiconductor
material according to claim 17, wherein the raw alloy comprises a
composition in which 0.01 to 10% of excess Te is added to the
stoichiometric composition of a compound thermoelectric
semiconductor comprising 40 atomic % of Bi, 50 to 59 atomic % of
Te, and 1 to 10 atomic % of Se.
20. The manufacturing method for a thermoelectric semiconductor
material according to claim 17, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; heating the raw material at a
temperature no lower than 380.degree. C. and no higher than
500.degree. C.
21. The manufacturing method for a thermoelectric semiconductor
material according to claim 18, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; thing the raw material at a
temperature no lower than 380.degree. C. and no higher than
500.degree. C.
22. The manufacturing method for a thermoelectric semiconductor
material according to claim 19, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by
along with applying pressure; heating the raw material at a
temperate no lower dm 380.degree. C. and no higher than 500.degree.
C.
23. The manufacturing method for a thermoelectric semiconductor
material according to claim 16, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
24. The manufacturing method for a thermoelectric semiconductor
material according to claim 17, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
25. The manufacturing method for a thermoelectric semiconductor
material according to claim 18, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
26. The manufacturing method for a thermoelectric semiconductor
material according to claim 19, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
27. The manufacturing method for a thermoelectric semiconductor
material according to claim 20, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
28. The manufacturing method for a thermoelectric semiconductor
material according to claim 21, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
29. The manufacturing method for a thermoelectric semiconductor
material according to claim 22, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
30. The manufacturing method for a thermoelectric semiconductor
material according to claim 16, wherein a rotational roll is used
as the cooling member and is rotated at a rate at which thickness
of the plate shaped raw thermoelectric semiconductor material
formed by supplying the molten raw alloy to the surface of the
cooling member and cooling and solidifying the molten alloy is at
least 30 .mu.m or greater.
31. The manufacturing method for a thermoelectric semiconductor
material according to claim 17, wherein a rotational roll is used
as the cooling member and is rotated at a rate at which thickness
of the plate shaped raw thermoelectric semiconductor material
formed by supplying the molten raw alloy to the surface of the
cooling member and cooling and solidifying the molten alloy is at
least 30 .mu.m or greater.
32. The manufacturing method for a thermoelectric semiconductor
material according to claim 18, when a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
33. The manufacturing method for a thermoelectric semiconductor
material according to claim 19, why a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
34. The manufacturing method for a thermoelectric semiconductor
material according to claim 20, wherein a rotational roll is used
as the cooling member and is rotated at a rate at which thickness
of the plate shaped raw thermoelectric semiconductor material
formed by supplying the molten raw alloy to the surface of the
cooling member and cooling and solidifying the molten alloy is at
least 30 .mu.m or greater.
35. The manufacturing method for a thermoelectric semiconductor
material according to claim 21, wherein a rotational roll is used
as the cooling member and is rotated at a rate at which thickness
of the plate shaped raw thermoelectric semiconductor material
formed by supplying the molten raw alloy to the surface of the
cooling member and cooling and solidifying the molten alloy is at
least 30 .mu.m or greater.
36. The manufacturing method for a thermoelectric semiconductor
material according to claim 22, wherein a rotational roll is used
as the cooling member and is rotated at a rate at which thickness
of the plate shaped raw thermoelectric semiconductor material
formed by supplying the molten raw alloy to the surface of the
cooling member and cooling and solidifying the molten alloy is at
least 30 .mu.m or greater.
37. A manufacturing method for a thermoelectric semiconductor
element, comprising: melting a raw alloy having a predetermined
composition of a thermoelectric semiconductor; having the raw alloy
to be contacted with a surface of a cooling member to form plate
shaped raw thermoelectric semiconductor materials; layering and
packing in approximately layered form the plate shaped raw
thermoelectric semiconductor materials to form a layered body;
solidifying and forming the layered body to form a compact;
applying presume to the compact in one of two axial directions
which are crossing each other in a plane approximately
perpendicular to the main layering direction of the raw
thermoelectric semiconductor materials, while preventing
deformation of the compact in the other axial direction; and
thereby applying shear force in an axial direction approximately
parallel to the main layering direction of the raw thermoelectric
semiconductor materials; and plastically deforming the compact to
form a thermoelectric semiconductor material; and cutting out a
thermoelectric semiconductor element from the thermoelectric
semiconductor material so that a plane approximately perpendicular
to the uniaxial direction in which the shear force is applied
during the plastic deformation of the compact can be used as a
contact surface with an electrode.
38. The manufacturing method for a thermoelectric semiconductor
element according to claim 37, wherein the raw alloy has a
composition in which excess Te is added to a predetermined
stoichiometric composition of a compound thermoelectric
semiconductor.
39. The manufacturing method for a thermoelectric semiconductor
element according to claim 38, wherein the stoichiometric
composition of the compound thermoelectric semiconductor is a
(Bi--Sb).sub.2Te.sub.3 based composition.
40. The manufacturing method for a thermoelectric semiconductor
element according to claim 39, when in the raw alloy comprises a
composition in which 0.1 to 5% of excess Te is added to the
stoichiometric composition of a compound thermoelectric
semiconductor comprising 7 to 10 atomic % of Bi, 30 to 33 atomic %
of Sb, and 60 atomic % of Te.
41. The manufacturing for a thermoelectric semiconductor element
according to claim 38, wherein the stoichiometric composition of
the compound thermoelectric semiconductor is a
Bi.sub.2(Te--Se).sub.3 based composition.
42. The manufacturing meted for a thermoelectric semiconductor
element according to claim 41, wherein the raw alloy comprises a
composition in which 0.01 to 10% of excess Te is added to the
stoichiometric composition of a compound thermoelectric
semiconductor comprising 40 atomic % of Bi, 50 to 59 atomic % of
Te, and 1 to 10 atomic % of Se.
43. The manufacturing method for a thermoelectric semiconductor
element according to claim 37, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; heating the raw material at a
temperature no lower than 380.degree. C. and no higher than
500.degree. C.
44. The manufacturing method for a thermoelectric semiconductor
element according to claim 38, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; heating the raw material at a temper
no lower than 380.degree. C. and no higher than 500.degree. C.
45. The manufacturing method for a thermoelectric semiconductor
element according to claim 39, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; heating the raw material at a
temperature no lower than 380.degree. C. and no higher than
500.degree. C.
46. The manufacturing method for a thermoelectric semiconductor
element according to claim 40, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; heating the raw material at a
temperature no lower than 380.degree. C. and no higher than
500.degree. C.
47. The manufacturing method for a thermoelectric semiconductor
element according to claim 41, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; heating the raw material at a
temperature no lower than 380.degree. C. and no higher than
500.degree. C.
48. The manufacturing method for a thermoelectric semiconductor
element according to claim 42, wherein solidification forming of
the raw thermoelectric semiconductor materials is carried out by:
along with applying pressure; heating the raw material at a
temperature no lower than 380.degree. C. and no higher than
500.degree. C.
49. The manufacturing method for a thermoelectric semiconductor
element according to claim 37, wherein, when the molten raw alloy
is contacted with a surf of a cooling member so as to form plate
shaped raw thermoelectric semiconductor materials, the molten alloy
is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
50. The manufacturing method for a thermoelectric semiconductor
element according to claim 38, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
51. The manufacturing method for a thermoelectric semiconductor
element according to claim 39, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shad raw thermoelectric semiconductor
material is not quenched.
52. The manufacturing method for a thermoelectric semiconductor
element according to claim 40, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
53. The manufacturing method for a thermoelectric semiconductor
element according to claim 41, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
54. The manufacturing method for a thermoelectric semiconductor
element according to claim 42, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
55. The manufacturing method for a thermoelectric semiconductor
element according to claim 43, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
56. The manufacturing method for a thermoelectric semiconductor
element according to claim 44, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
57. The manufacturing method for a thermoelectric semiconductor
element according to claim 45, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
58. The manufacturing method for a thermoelectric semiconductor
element according to claim 46, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
59. The manufacturing method for a thermoelectric semiconductor
element according to claim 47, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials, the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
60. The manufacturing method for a thermoelectric semiconductor
element according to claim 48, wherein, when the molten raw alloy
is contacted with a surface of a cooling member so as to form the
plate shaped raw thermoelectric semiconductor materials the molten
alloy is cooled and solidified at a rate at which 90% or more of a
thickness of the formed plate shaped raw thermoelectric
semiconductor material is not quenched.
61. The manufacturing method for a thermoelectric semiconductor
element according to claim 37, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
62. The manufacturing method for a thermoelectric semiconductor
element according to claim 38, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
63. The manufacturing method for a thermoelectric semiconductor
element according to claim 39, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
64. The manufacturing method for a thermoelectric semiconductor
element according to claim 40, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
65. The manufacturing method for a thermoelectric semiconductor
element according to claim 41, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
66. The manufacturing method for a thermoelectric semiconductor
element according to claim 42, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
67. The manufacturing method for a thermoelectric semiconductor
element according to claim 43, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate sped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
68. The manufacturing method for a thermoelectric semiconductor
element according to claim 44, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
69. The manufacturing method for a thermoelectric semiconductor
element according to claim 45, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
70. The manufacturing method for a thermoelectric semiconductor
element according to claim 46, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
um or greater.
71. The manufacturing method for a thermoelectric semiconductor
element according to claim 47, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
72. The manufacturing method for a thermoelectric semiconductor
element according to claim 48, wherein a rotational roll is used as
the cooling member and is rotated at a rate at which thickness of
the plate shaped raw thermoelectric semiconductor material formed
by supplying the molten raw alloy to the surface of the cooling
member and cooling and solidifying the molten alloy is at least 30
.mu.m or greater.
73. A manufacturing method for a thermoelectric module comprising:
melting a raw alloy having a composition of P type thermoelectric
semiconductor, and a raw alloy having a composition of N type
thermoelectric semiconductor respectively; having the each raw
alloy to be contacted with a surface of a cooling member to form
plate shaped raw thermoelectric semiconductor materials having a
composition of P type thermoelectric semiconductor and plate shaped
raw thermoelectric semiconductor materials having a composition of
N type thermoelectric semiconductor respectively; having the P type
and N type raw thermoelectric semiconductor materials layered
approximately parallel in a direction of plate thickness to form
layered bodies; solidifying and forming the layered bodies to form
compacts; applying pressure to each of the compacts having the
compositions of P type and N type thermoelectric semiconductor in
one of two axial directions which are crossing each other in a
plane approximately perpendicular to the main layering direction of
the raw thermoelectric semiconductor materials, while preventing
deformation of the compact in the other axial direction; and
thereby applying shear force in an axial direction approximately
parallel to the main layering direction of the raw thermoelectric
semiconductor materials; and plastically deforming the comes to
form P type and N type thermoelectric semiconductor materials;
cutting out P type and N type thermoelectric semiconductor elements
from the P type and N type thermoelectric semiconductor materials
so that a plane approximately perpendicular to the uniaxial
direction in which the shear force is applied during the plastic
deformation of the compact can be used as a contact surface with an
electrode; arranging the P type and N type thermoelectric
semiconductor elements so that the elements are aligned in the
direction perpendicular to the axial direction of pressure
application during plastic deformation of a compact, and also
perpendicular to the direction of shear force by the pressure
application; joining the P type and N type elements via a metal
electrode to form a PN element pair.
74. The manufacturing method for a thermoelectric module according
to claim 73, wherein the raw alloy of each of the P type and N type
thermoelectric semiconductors has a composition in which excess Te
is added to a predetermined stoichiometric composition of a
compound thermoelectric semiconductor.
75. The manufacturing method for a thermoelectric module according
to claim 74, wherein the stoichiometric composition of the P type
compound thermoelectric semiconductor is a (Bi--Sb).sub.2Te.sub.3
based composition.
76. The manufacturing method for a thermoelectric module according
to claim 75, wherein the raw alloy of the P type thermoelectric
semiconductor comprises a composition in which 0.1 to 5% of excess
Te is added to the stoichiometric composition of a compound
thermoelectric semiconductor comprising 7 to 10 atomic % of Bi, 30
to 33 atomic % of Sb, and 60 atomic % of Te.
77. The manufacturing method for a thermoelectric module according
to claim 74, wherein the stoichiometric composition of the N type
compound thermoelectric semiconductor is a Bi.sub.2(Te--Se).sub.3
based composition.
78. The manufacturing method for a thermoelectric module according
to claim 77, wherein the raw alloy of the N type thermoelectric
semiconductor wherein the raw alloy comprises a composition in
which 0.01 to 10% of excess Te is added to the stoichiometric
composition of a compound thermoelectric semiconductor comprising
40 atomic % of Bi, 50 to 59 atomic % of Te, and 1 to 10 atomic % of
Se.
79. The manufacturing method for a thermoelectric module according
to claim 74, wherein solidification forming of the raw
thermoelectric semiconductor materials is carried out by: along
with applying pressure; heating the raw material at a temperature
no lower than 380.degree. C. and no higher than 500.degree. C.
80. The manufacturing method for a thermoelectric module according
to claim 75, wherein solidification forming of the raw
thermoelectric semiconductor materials is carried out by: along
with applying pressure; heating the raw material at a temperature
no lower than 380.degree. C. and no higher than 500.degree. C.
81. The manufacturing method for a thermoelectric module according
to claim 76, wherein solidification forming of the raw
thermoelectric semiconductor materials is carried out by: along
with applying pressure; heating the raw material at a temperature
no lower than 380.degree. C. and no higher than 500.degree. C.
82. The manufacturing method for a thermoelectric module according
to claim 77, wherein solidification forming of the raw
thermoelectric semiconductor materials is carried out by: along
with applying pressure; heating the raw material at a temperate no
lower than 380.degree. C. and no higher than 500.degree. C.
83. The manufacturing method for a thermoelectric module according
to claim 78, wherein solidification forming of the raw
thermoelectric semiconductor materials is carried out by: along
with applying pressure; heating the raw material at a temperature
no lower than 380.degree. C. and no higher than 500.degree. C.
84. The manufacturing method for a thermoelectric module according
to claim 73, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shad raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
85. The manufacturing method for a thermoelectric module according
to claim 74, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
86. The manufacturing method for a thermoelectric module according
to claim 75, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
87. The manufacturing method for a thermoelectric module according
to claim 76, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor material, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
88. The manufacturing method for a thermoelectric module according
to claim 77, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
89. The manufacturing method for a thermoelectric module according
to claim 78, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
90. The manufacturing method for a thermoelectric module according
to claim 79, where, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
91. The manufacturing method for a thermoelectric module according
to claim 80, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
92. The manufacturing method for a thermoelectric module according
to claim 81, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
93. The manufacturing method for a thermoelectric module according
to claim 82, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
94. The manufacturing method for a thermoelectric module according
to claim 83, wherein, when the molten raw alloy is contacted with a
surface of a cooling member so as to form the plate shaped raw
thermoelectric semiconductor materials, the molten alloy is cooled
and solidified at a rate at which 90% or more of a thickness of the
formed plate shaped raw thermoelectric semiconductor material is
not quenched.
95. The manufacturing method for a thermoelectric module according
to claim 73, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which the thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
96. The manufacturing method for a thermoelectric module according
to claim 74, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 sun or
greater.
97. The manufacturing method for a thermoelectric module according
to claim 75, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
98. The manufacturing method for a thermoelectric module according
to claim 76, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
99. The manufacturing method for a thermoelectric module according
to claim 77, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
100. The manufacturing method for a thermoelectric module according
to claim 78, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
101. The manufacturing method for a thermoelectric module according
to claim 79, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
102. The manufacturing method for a thermoelectric module according
to claim 80, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the su of the cooling member and
cooling and solidifying the molten alloy is at least 30 .mu.m or
greater.
103. The manufacturing method for a thermoelectric module according
to claim 81, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
104. The manufacturing method for a thermoelectric module according
to claim 82, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
105. The manufacturing method for a thermoelectric module according
to claim 83, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
106. The manufacturing method for a thermoelectric module according
to claim 84, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
107. The manufacturing method for a thermoelectric module according
to claim 85, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
108. The manufacturing method for a thermoelectric module according
to claim 86, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
109. The manufacturing method for a thermoelectric module according
to claim 87, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
110. The manufacturing method for a thermoelectric module according
to claim 88, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
111. The manufacturing method or a thermoelectric module according
to claim 89, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
112. The manufacturing method for a thermoelectric module according
to claim 90, wherein a rotational roll is used as the cooling
member and is red at a rate at which thickness of the plate shaped
raw thermoelectric semiconductor material formed by supplying the
molten raw alloy to the surface of the cooling member and cooling
and solidifying the molten alloy is at least 30 .mu.m or
greater.
113. The manufacturing method for a thermoelectric module according
to claim 91, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
114. The manufacturing method for a thermoelectric module according
to claim 92, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
115. The manufacturing method for a thermoelectric module according
to claim 93, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
116. The manufacturing method for a thermoelectric module according
to claim 94, wherein a rotational roll is used as the cooling
member and is rotated at a rate at which thickness of the plate
shaped raw thermoelectric semiconductor material formed by
supplying the molten raw alloy to the surface of the cooling member
and cooling and solidifying the molten alloy is at least 30 .mu.m
or greater.
Description
TECHNICAL FIELD
[0001] The present invention relates to a thermoelectric
semiconductor material as well as to a thermoelectric semiconductor
element, a thermoelectric module, and manufacturing method for same
that are utilized for thermoelectric cooling, thermoelectric
heating, thermoelectric power generation or the like.
BACKGROUND ART
[0002] Devices for carrying out thermoelectric cooling,
thermoelectric heating and thermoelectric power generation using
the thermoelectric properties of a thermoelectric semiconductor
generally have a basic configuration where a plurality of
thermoelectric modules 1 are aligned and connected in series, as
shown schematically in the example of FIG. 27. In each of the
thermoelectric modules 1, a PN element pair is formed by joining a
P type thermoelectric semiconductor element 2 to an N type
thermoelectric semiconductor element 3 via a metal electrode 4.
[0003] One type of thermoelectric semiconductor that forms above
described thermoelectric semiconductor elements 2 and 3 uses a
complex compound made of one or two elements selected from bismuth
(Bi) and antimony (Sb) of 5B group, and one or two elements
selected from tellurium (Te) and selenium (Se) of 6B group. The
thermoelectric semiconductor is made of an alloy having a
(Bi--Sb).sub.2(Te--Se).sub.3 based composition in which the ratio
of a number of atoms of 5B group elements (Bi and Sb) to a number
of atoms of 6B group elements (Te and Se) is 2:3.
[0004] Above-described alloy having a (Bi--Sb).sub.2(Te--Se).sub.3
based composition for forming the thermoelectric semiconductor, has
a hexagonal strut and electrical and thermal anisotropy due to the
crystal structure. It is known that by conveying electricity or
heat in the <110> direction of the crystal structure, that
is, along C face of the hexagonal structure, excellent
thermoelectric performance can be obtained, in comparison with a
case where electricity or heat is conveyed in the direction of
c-axis.
[0005] Conventionally, raw alloys prepared so as to have the
above-described desired composition are heated and melted to form
molten alloys. Subsequently, using a directional solidification
method, such as a zone melting method, while controlling the
direction of the crystal growth so that the crystal has an
excellent thermoelectric performance along the growth direction, a
single crystalline or a polycrystalline ingot is manufactured as a
thermoelectric semiconductor material. By a requited working of the
ingot, such as cutting a portion having little irregularity in the
composition from the ingot and working the cut portion, an element
having an excellent properties is manufactured.
[0006] However, the ingots converted to single crystal using the
zone melting method have significant cleavage due to their crystal
structure. Therefore, when a thermoelectric semiconductor element
is manufactured by slicing or the like of the ingot as a
thermoelectric semiconductor material, there is a problem that the
insufficient mechanical strength cause a reduction of yields by
cracking or chipping. Therefore, it has been desired to improve
thermoelectric performance along with increasing the strength of
thermoelectric semiconductor materials for thermoelectric
semiconductor elements.
[0007] In order to improve the strength and thermoelectric
performance of thermoelectric semiconductors, one technique is
proposed in which an ingot as a thermoelectric semiconductor
material which has been manufactured in the same manner as
described above by a directional solidification method, is worked
by extrusion or roiling so as to apply shear force in the direction
of C face of a hexagonal structure, and thereby improving the
strength of the material (see, for example, Patent Document 1).
[0008] There has been proposed several method in view of general
properties of polycrystalline metallic material as following:
Crystal grains of polycrystalline metallic material show dispersive
distribution of orientation, the metallic material exhibits
isotropy. When the crystal grains are oriented in a specific
direction as a result of a working such as plastic working, crystal
anisotropy of individual crystal grains appears as macroscopic
characteristics so that the metallic material as a whole exhibits
anisotropy (for example, Non-Patent Document 1). By crushing raw
alloy powder and sintering the powder, mechanical property of the
material is improved in the sintered body. In the sintered body
crystalline orientation is reduced, since the integration of
randomly oriented powder grains during the sintering process
orientates constituent crystals randomly. By rolling the sintered
body in a direction (see, for example, Patent Document 2), by
extrusion molding the sintered body (see, for example, Patent
Documents 3 and 4), or by plastically deforming the sintered body
(see, for example Patent Documents 5, 6, 7, 8, 9 and 10),
uniformity of crystalline orientation of the sintered body is
improved.
[0009] That is to say, by applying a pressing force on the
above-described sintered body, and plastically deforming the
sintered body, constituent crystals of the texture are plastically
deformed and flattened in a direction perpendicular to the
direction of pressing force, and thus, the crystals are oriented in
such a manner that the cleavage plane are perpendicular to the
direction of compression. In a rolling or a forging by an uniaxial
compression, C face of the hexagonal structure is oriented in the
direction perpendicular to the direction of compressing the
sintered body (direction of pressing). In an extrusion molding, C
face of the hexagonal structure is oriented along the direction of
extrusion (direction of pressing). By this method, it is possible
to prepare a thermoelectric semiconductor material in which
crystals are oriented in a direction of excellent thermoelectric
performance.
[0010] In general, the thermoelectric performance of the material
used for the manufacture of a thermoelectric semiconductor is
expressed by the following equation:
Z=.alpha..sup.2.sigma./.kappa.=.alpha..sup.2/(.rho..kappa.) where Z
is a Figure-of-Merit, .alpha. is the Seebeck coefficient, .sigma.
is electric conductivity, .kappa. is thermal conductivity, and
.rho. is resistivity.
[0011] Accordingly, in order to increase the thermoelectric
performance (Figure-of-Merit Z) of a thermoelectric semiconductor
material, a raw alloy material in which the value of the Seebeck
coefficient (.alpha.) or the electric conductivity (.sigma.) is
increased or the thermal conductivity (.kappa.) is lowered, may be
utilized. Judging from this, it should be possible to increase
thermoelectric performance (Figure-of-Merit Z) by decreasing the
grain sizes of crystals and reducing the conductivity (.kappa.).
However, in the above-described techniques using a powder produced
by crushing an ingot of the raw alloy, the particle sizes of the
powder is the grain sizes of crystals, therefore there is a limit
to the miniaturiztion of crystal grains formed by crushing.
Therefore, in order to improve the strength and thermoelectric
performance of a thermoelectric semiconductor material, still
another technique has been proposed. A raw alloy is melted into a
molten alloy. A raw thermoelectric semiconductor material in a
ribbon, foil piece or powder form is formed by a liquid quenching
method such as rotational roll method in which the molten alloy is
sprayed onto the surface of a rotational roll which is being
rotated or a gas atomizing method in which the molten alloy is
sprayed into a predetermined gas flow. At that time, microscopic
crystal grains are formed within the texture of the raw
thermoelectric semiconductor material, and high density strain and
defects are introduced into the texture. After the raw
thermoelectric semiconductor material is crushed into a powder,
this raw thermoelectric semiconductor material in powder form is
heat treated and solidified, and thereby a thermoelectric
semiconductor material is manufactured. By this method, during the
heat treatment or the solidification process, recrystallization of
crystals occurs ling the distortion due to the defects as a driving
force, and due to the presence of grain boundaries, the thermal
conductivity (.kappa.) is lowered and thermoelectric performance
(Figure-of-Merit Z) is increased (see, for example, Patent Document
11).
[0012] As the rotational velocity of a rotational roll that is used
to form a raw thermoelectric semiconductor material in a ribbon,
foil piece or powder form by quenching a molten alloy, it is
proposed to set a circumferential velocity to be 2 to 80 m/sec, so
as to effectively generate microscopic crystals by quenching, and
make the crystals grow in the direction of heat flow (see, for
example, Patent Document 12). In this case, a sufficient quenching
speed is not achieved when the circumferential velocity of the
rotational roll is less than 2 m/sec, and a sufficient quenching
speed is also not achieved when the circumferential velocity is 80
m/sec or greater.
[0013] As the heating conditions when the raw thermoelectric
semiconductor material in a ribbon, foil or powder form is
solidified and formed, it is proposed to maintain the material at a
temperature from 200 to 400.degree. C. or at a temperature from 400
to 600.degree. C. for 5 to 150 minutes while applying pressure to
the material (see, for example, Patent Document 13).
[0014] Another technique for increasing the thermoelectric
performance of a thermoelectric semiconductor material is proposed,
in which Ag is added to and mixed with a raw thermoelectric
semiconductor material in a ribbon, foil piece or powder form that
has been formed by quenching a molten alloy of a
(Bi--Sb).sub.2(Te--Se).sub.3 based raw alloy, on a rotational roll.
By subsequent sintering and solidification, Ag is distributed in
the grain boundaries, so that resistivity .rho. is lowered, and
thus, an increase in the thermoelectric performance
(Figure-of-Merit Z) can be achieved (see, for example, Patent
Document 14).
[0015] It is known that in a rotational rolling method as the
liquid quenching method, a molten alloy sprayed onto the surface of
a rotational roll is cooled from contact surface with the
rotational roll in the direction toward the outer periphery of the
roll. Together with this quenching, the molten alloy solidifies in
the direction of the film thickness. As a result, a raw
thermoelectric semiconductor material in foil form is produced, in
which C face, the base plane of the hexagonal structure of the
crystal gains, stand in the direction of the film thickness.
[0016] Therefore, a technique for effectively using the orientation
of the crystals of a raw thermoelectric semiconductor material that
has been manufactured by the rotational rolling method is proposed,
in which the raw thermoelectric semiconductor materials are layered
in the direction of the film thickness, and are sintered while
pressure is applied in the direction parallel to the direction of
the film thickness, and thereby, a thermoelectric semiconductor
material is manufactured (see, for example, Patent Document
15).
[0017] Furthermore, techniques for manufacturing a thermoelectric
semiconductor material in which crystal orientation is improved
have been proposed. In a technique, a layered body is produced by
layering raw thermoelectric semiconductor materials manufactured by
a rotational rolling method, and integrating the layered body
layered in the direction of the film thickness by applying a in the
direction parallel to the layering direction. During the pressing
for integrating the layers in the direction parallel to the
layering direction, crystal orientation of each layers are
disordered at the interface of the layers. By applying pressure in
the direction perpendicular to the layering direction of the
layered body, such disorder of crystal orientation at the interface
can be improved (see, for example, Patent Document 16). In another
technique, a layered body is produced by layering raw
thermoelectric semiconductor materials in foil powder form in the
direction of the film thickness. Crystalline orientation of the
layered body is improved by applying pressure in at least three
directions perpendicular to the layering direction. Furthermore,
the layered body, the crystalline orientation of which has been
improved by the above-described application of pressure, is formed
by extrusion molding in the direction parallel to the layering
direction, and thereby uniformity in the orientation of the
crystals is additionally increased (see, for example, Patent
Document 17).
[0018] Recently, it has been desired for a thermoelectric
transducing material to be provided with further improved
performance and high reliability. Together with an increase in
performance, an inclease in mechanical strength and excellence in
workability are also desired. For example, when a thermoelectric
semiconductor is used to cool a laser oscillator, N type and P type
thermoelectric semiconductor elements having dimensions of no
greater than 1 mm are used as modules. Accordingly, it is required
a mechanical strength sufficient to make it possible for a
thermoelectric semiconductor element of no greater than 1 mm in
dimension to be sliced from an ingot of a thermoelectric
semiconductor material without chipping.
[List of Prior Art Documents]
(1) Patent Document 1: Japanese Unexamined Patent Application,
First Publication No. H11-163422
(2) Pat Document 2: Japanese Unexamined Patent Application, First
Publication No. S63-138789
(3) Patent Document 3: Japanese Unexamined Patent Application,
First Publication No. 2000-124512
(4) Patent Document 4: Japanese Unexamined Patent Application,
First Publication No. 2001-345487
(5) Patent Document 5: Japanese Unexamined Patent Application,
First Publication No. 2002-118299
(6) Patent Document 6: Japanese Unexamined Patent Application,
First Publication No. H10-178218
(7) Patent Document 7: Japanese Unexamined Patent Application,
First Publication No. 2002-151751
(8) Patent Document 8: Japanese Unexamined Patent Application,
First Publication No. H11-261119
(9) Patent Document 9: Japanese Unexamined Patent Application,
First Publication No. H10-178219
(10) Patent Document 10: Japanese Unexamined Patent Application,
First Publication No. 2002-111086
(11) Patent Document 11: Japanese Unexamined Patent Application,
First Publication No. 2000-36627
(12) Patent Document 12: Japanese Unexamined Patent Application,
First Publication No. 2000-286471
(13) Patent Document 13: Japanese Unexamined Patent Application,
First Publication No. 2000-332307
(14) Patent Document 14: Japanese Unexamined Patent Application,
First Publication No. H8-199291
(15) Patent Document 15: Japanese Patent Publication No.
2659309
(16) Patent Document 16: Japanese Unexamined Patent Application,
First Publication No. 2001-53344
(17) Patent Document 17: Japanese Unexamined Patent Application,
First Publication No. 2000-357821
(18) Non-Patent Document 1: "Elastic Constants of Al--Cu Alloys
Containing Columnar Crystals" by Hiroshi Kato and Keiji Yoshikawa,
Materials (Journal of the Society of Materials Science, Japan)
Volume 30, No. 331, April 1981, p. 85.
[0019] There is a problem, however, in that the mechanical strength
of a thermoelectric semiconductor material cannot be sufficiently
enhanced, even when the thermoelectric semiconductor material is
manufactured by plastically deforming an ingot of a thermoelectric
semiconductor raw alloy, as shown in Patent Document 1.
[0020] At present, it is difficult to overcome the problem in which
a single-crystal or directionally solidified ingot easily cracks
along the cleavage plane of the material. Even though the
orientation of the crystals is uniform, there are few methods for
still increasing performance, because the manufacturing methods are
limited.
[0021] Among techniques for manufacturing a polycrystalline
thermoelectric semiconductor material, as shown in Patent Documents
2 to 10, by a technique for plastically deforming a sintered body
by rolling, by an extrusion molding, or by upsetting forging of the
sintered body formed by sintering of powder produced by crushing an
ingot of an alloy material, it should be possible to enhance the
mechanical strength of a thermoelectric semiconductor material.
However, the size of the powder particles determine the diameter of
the crystal grains in the powder of the ingot, and there is a limit
to the miniaturization of the cry grains. Therefore, the
thermoelectric semiconductor material is disadvantageous in
reducing thermal conductivity (a) and the thermoelectric
performance cannot be significantly enhanced. In addition, since
the powder is sintered in a state in which each powder particles
are randomly oriented, by the plastic deformation of the sintered
body having such disordered crystalline orientation, it is
difficult to enhance the crystalline orientation of a tenure of
thermoelectric semiconductor material.
[0022] Furthermore, in the technique disclosed in Patent Document
11, electric conductivity (.sigma.) is increased by heat treatment
or sintering in order to remove defects within the grains, and
thermal conductivity (.kappa.) is reduced due to scattering of
phonons of the crystal grain boundaries. However, the grain
boundaries inevitably exist in a polycrystalline body. Therefore,
at present, it is difficult to increase electric conductivity and
to reduce thermal conductivity at the same time. In addition, there
is a problem in that the electric resistance is lowered in the
vicinity of grain boundaries where the impurities are concentrated,
whereas inside of the grains which mainly make up the volume are
converted to semiconductors, and thus, electric resistance
increases.
[0023] As a rotational speed of the rotational roll for
manufacturing a raw thermoelectric semiconductor material in foil
or powder form, Patent Document 12 discloses that the
circumferential velocity of a rotational roll may be set at 2 to 80
nm/sec. However, Patent Document 12 does not show any concrete
processes for manufacturing a thermoelectric semiconductor material
by solidifying and forming a raw thermoelectric semiconductor
material in foil or powder form that has been manufactured by using
a rotational roll of which the circumferential velocity has been
set as described above.
[0024] As a heating condition for sintering a raw thermoelectric
semiconductor material that has been manufactured by a liquid
quenching method, Patent Document 13 discloses that the temperature
may be set in a range from 200 to 60.degree. C. This is the setting
of a temperature condition that allows sintering without losing
uniformity in the orientation of the crystals within the texture of
the raw thermoelectric semiconductor material, but is totally
different from the temperature range for the setting of the
temperature when a raw thermoelectric semiconductor material is
solidified and formed according to the present invention as
described below where segregation, dropping of separated phase,
liquid deposition, and the like of a Te rich phase having a low
melting point are completely prevented during solidification
forming of a raw thermoelectric semiconductor material.
[0025] By a technique, as proposed in Patent Document 14, for
dispersing Ag in the crystal grain boundaries and lowering
resistivity (.rho.), and thereby, achieving an increase in the
thermoelectric performance, Ag serves as a dopant in a
(Bi--Sb).sub.2(Te--Se).sub.3 based thermoelectric semiconductor.
Therefore, the technique includes a problem in that the added
amount of Ag must be strictly adjusted, and also includes a problem
of age deterioration.
[0026] In the technique described in Patent Document 15, raw
thermoelectric semiconductor materials in foil forms manufactured
by the rotational rolling method are layered in the direction of
the film thickness and are solidified and formed. Therefore, there
is a problem in which the crystal orientation of the layered raw
thermoelectric semiconductor material is disordered when pressure
is applied in the direction parallel to the direction of the film
thickness.
[0027] When raw thermoelectric semiconductor materials in foil
forms manufactured by a rotational rolling method are layered, and
pressure is applied to the layered body in the direction
perpendicular to the layering direction, and pressure is applied to
layered body, as described in Patent Document 16, in a direction
perpendicular to the layering direction, or as described in Patent
Document 17, in at least three direction perpendicular to the
layering direction, it should be possible to improve crystal
orientation of the texture. In these case, an improvement of
crystalline orientation is achieved by making the direction of C
face of the hexagonal structure stand in the layering direction of
the raw thermoelectric semiconductor material. However, the
direction of c-axis of the hexagonal structure in each crystal
grain cannot be uniformly oriented. Therefore the direction of
c-axis of the hexagonal structure of the crystal grains cannot be
uniformly oriented even when an extrusion molding is additionally
and sequentially carried out by applying pressure in the layering
direction, as described in Patent Document 17.
[0028] In conventional manufacturing methods for a polycrystalline
thermoelectric semiconductor materials as described in Patent
Documents 2 to 17, powders of ingots to be solidified and formed
for the manufacture of a thermoelectric semiconductor material, and
raw thermoelectric semiconductor materials in ribbon, foil, and
powder form produced by a liquid quenching method have fine grain
sizes. Therefore raw thermoelectric semiconductor materials have
large specific surface area and their surfaces are easily oxidized.
In addition, even when reduction process is carried out on each of
the raw materials in order to prevent the surface oxidation, there
are many operations to be added such as sealing a material in a
mold without allowing contact with oxygen during sintering. Even
when such additional operations are carried out, it is difficult to
reduce influence of oxidization.
[0029] In addition, since each of the above-described raw materials
has fine grain size, it is difficult to increase density of the
material during sintering. For example, when a raw thermoelectric
semiconductor material in fine foil form that has been manufactured
by a rotational rolling method and is sintered at 475.degree. C.,
the increase of density is only within a range of 98 to 991%. When
a powder is sintered, reduction of density depends on the grain
size, but is limited to approximately 95%. Therefore, there is a
possibility that the electric conductivity being lowered.
[0030] Furthermore, in a general hot pressing, a fine powder is
used in order to obtain the compact texture after sintering. It is
known that bulk density increase with decreasing particle size of
powder due to increasing amount, of air, but it is possible to gain
a compact structure by applying pressure. Therefore, in the
techniques described in Patent Documents 15 to 17, in which raw
thermoelectric semiconductor materials in foil forms manufacture by
rotational rolling methods are layered and subsequently solidified
and formed, fine foils are used as the raw thermoelectric
semiconductor materials. However, since the densification of
sintered texture by hot press is a phenomena occurring as a result
of powder flow and plastic deformation of powder particles, when
fine foils of raw thermoelectric semiconductor materials are
solidified, as described in Patent Documents 15 to 17, a large
portion of each raw thermoelectric semiconductor material is
plastically deformed and in a great number of portions, the
original crystalline orientation of the foil is disordered, and an
orientation of C face is easily disordered.
DISCLOSURE OF INVENTION
[0031] Therefore, an object of the present invention is to provide
a thermoelectric semiconductor material having excellent
crystalline orientation in the texture, reduced oxygen
concentration, and enhanced thermoelectric performance, as well as
to provide a thermoelectric semiconductor element using such a
thermoelectric semiconductor material, a thermoelectric module
using such a thermoelectric element, and manufacturing methods for
same.
[0032] In order to achieve the above-described objects, the sent
invention provides a thermoelectric semiconductor material which is
produced by: layering and packing raw thermoelectric semiconductor
materials made of a raw alloy having a predetermined composition of
a thermoelectric semiconductor to form a layered body; solidifying
and forming the layered body to form a compact; applying pressure
to the compact in a uniaxial direction that is perpendicular or
nearly perpendicular to the main layering direction of the raw
thermoelectric semiconductor materials; and thereby applying shear
force in a uniaxial direction that is approximately parallel to the
main layering direction of the raw thermoelectric semiconductor
materials, and plastically deforming the compact.
[0033] When a raw alloys is contacted with the surface of a cooling
member at the time of the manufacture of the thermoelectric
semiconductor material, a raw thermoelectric semiconductor material
is achieved, in which C face of the hexagonal structure of the
crystal grains are oriented approximately parallel to the direction
of the plate thickness. When the raw thermoelectric semiconductor
materials are layered in the direction of the plate thickness to
form a layered body, and then solidified and formed, the direction
of extension of C face of the crystal grains is maintained to be
oriented in the layering direction in the compact. Furthermore,
when pressure is applied to the compact in such a manner that shear
force is applied in a uniaxial direction approximately parallel to
the main layering direction of the thermoelectric semiconductor,
which is approximately similar to the extending direction of C face
of the crystal grains and thereby the compact is plastically
deformed, the crystal grains are flattened along the direction in
which shear force is applied, and the extending direction of C face
remain to be oriented in the direction of shear force during the
plastic deformation. At the same time, the directions of c-axes of
the crystal grains are oriented approximately parallel to the
direction in which pressure is applied for the plastic deformation.
Accordingly, in the texture of achieved thermoelectric
semiconductor material, both the extending direction of C face and
the direction of c-axis in the hexagonal structure of crystal
grains are uniformly oriented, and therefore high thermoelectric
performance can be obtained by setting current and heat to be
conveyed in the extending direction of C face.
[0034] Accordingly, a thermoelectric semiconductor material having
an excellent thermoelectric performance can be achieved by a
manufacturing method for a thermoelectric semiconductor material
comprising: melting a raw alloy having a predetermined composition
of thermoelectric semiconductor; subsequently having the molten
alloy contacted with a surface of a cooling member and thereby
forming plate shaped raw thermoelectric semiconductor materials;
layering the plate shaped raw thermoelectric semiconductor
materials in a direction approximately parallel to a direction of
the plate thickness and solidifying and forming the layered body
into a compact; applying pressure to the compact in one of two
axial directions which are crossing each other in a plane
approximately perpendicular to the main layering direction of the
raw thermoelectric semiconductor materials, while preventing
deformation of the compact in the other axial direction; and
thereby applying shear force in an axial direction approximately
parallel to the main layering direction of the raw thermoelectric
semiconductor materials, and plastically deforming the compact to
form a thermoelectric semiconductor material.
[0035] In addition, when a thermoelectric semiconductor material
has a compound phase comprising: complex compound semiconductor
phase having a predetermined stoichiometric composition of a
compound thermoelectric semiconductor, and a Te rich phase in which
excess Te is added to the above composition, crystal grain
boundaries exist in the thermoelectric semiconductor material, and
crystal strain is generated due to the presence of the compound
phase of complex compound semiconductor phase and the Te rich
phase. By the introduction of crystal strain, thermal conductivity
can be lowered, and therefore, the Figure-of-Merit can be increased
as a result of the lowering of thermal conductivity.
[0036] Furthermore, when a thermoelectric semiconductor material is
produced by: adding excess Te to a predetermined stoichiometric
composition of a compound thermoelectric semiconductor to form a
raw alloy; layering and packing plate shaped raw thermoelectric
semiconductor materials made of the raw alloy to form a layered
body; solidifying and forming the layered body to form a compact;
applying pressure to the compact in an axial direction
perpendicular or nearly perpendicular to the main layering
direction of the raw thermoelectric semiconductor materials; and
thereby applying shear force in an axial direction approximately
parallel to the main layering direction of the raw thermoelectric
semiconductor materials, and plastically deforming the compact, the
thermoelectric semiconductor material is provided with excellent
crystalline orientation in which both extending direction of C face
and direction of c-axes of the hexagonal structure of the crystal
grains are approximately uniformly oriented. In addition, due to
the presence of the compound phase of complex compound
semiconductor phase and the Te rich phase, thermal conductivity can
be lowered, and therefore, the Figure-of-Merit can be further
increased.
[0037] Accordingly, a manufacturing method for a thermoelectric
semiconductor material, in which a raw alloy is controlled to have
a composition where an excess Te is added to the predetermined
stoichiometric composition of a compound thermoelectric
semiconductor can provide a thermoelectric semiconductor having
excellent crystalline orientation, a compound phase of complex
compound semiconductor phase and the Te rich phase, and a high
Figure-of-Merit.
[0038] In the above described method, a P type thermoelectric
semiconductor material having high thermoelectric performance can
be produced by controlling the raw alloy to have a composition in
which excess Te is added to a (Bi--Sb).sub.2Te.sub.3 based
stoichiometric composition, concretely, by controlling the raw
alloy to have a composition in which 0.1 to 5% of excess Te is
added to the stoichiometric composition of a compound
thermoelectric semiconductor comprising 7 to 10 atomic % of Bi, 30
to 33 atomic % of Sb, and 60 atomic % of Te.
[0039] On the other hand, a N type thermoelectric semiconductor
material having high thermoelectric performance as described above
can be produced by controlling the raw alloy to have a composition
in which excess Te is added to a Bi.sub.2(Te--Se).sub.3 based
stoichiometric composition, concretely, by controlling the raw
alloy to have a composition where 0.01% to 10% of excess Te is
added to the stoichiometric composition of a compound
thermoelectric semiconductor comprising 40 atomic % of Bi, 50 to 59
atomic % of Te, and 1 to 10 atomic % of Se.
[0040] Furthermore, when the solidification forming of the raw
thermoelectric semiconductor materials is carried out by applying
pressure and by heating to a temperature no less than 380.degree.
C. and no higher than 500.degree. C., the thermoelectric
semiconductor material can be solidified and formed in a state in
which the Te rich phase in the raw thermoelectric semiconductor
material is prevented from being converted to liquid phase, or the
Te rich liquid phase is controlled to be a small amount. Therefore,
a P type or N type thermoelectric semiconductor material can be
formed, having a multi phase structure of the P type or N type
complex compound semiconductor phase dispersing microscopic Te rich
phases including an excess Te in the above semiconductor
composition.
[0041] Moreover, in the manufacturing method, when a molten alloy
of the raw alloy is contacted with the surface of a cooling member
to form a plate shaped raw thermoelectric semiconductor material,
the cooling rate of the molten alloy during solidification may be
controlled to a rate by which 90% or more of the thickness of the
plate shaped raw thermoelectric semiconductor material is not
quenched. Concretely, a rotational roll may be used as the cooling
member, and when the plate shaped raw thermoelectric semiconductor
material is formed by supplying the molten alloy of the raw alloy
to the surface of such cooling member, the rotational roll may be
rotated at a rate at which the thickness of the raw thermoelectric
semiconductor material is controlled to be at least no less than 30
.mu.m. By this method, microscopic crystal nuclei are formed on the
side of contact surface of the molten raw alloy and the cooling
member, and the molten alloy can be slowly solidified so that, from
the nuclei, large crystal grains grow in the direction of the
thickness, and the raw thermoelectric semiconductor material can be
formed to have a thickness of no less than 30 .mu.m. At at time,
the crystal grains can be grown in such a manner that C face of the
hexagonal structure of the crystals extend in the direction of
thickness, approximately throughout the entire thickness of the raw
thermoelectric semiconductor material. When the raw alloy is made
to have a composition including excess Te, in the
(Bi--Sb).sub.2Te.sub.3 based P type complex compound semiconductor
phase or in the Bi.sub.2(Te--Se).sub.3 based N type complex
compound semiconductor phase, the Te rich phases including excess
Te in each of the above compositions can be microscopically
dispersed as separated phase without being converted to amorphous
phase. Thus, the Te rich phase precipitate as hetero phase or
nucreate as hetero phase nuclei within crystal grains or in grain
boundaries of the complex compound semiconductor, and thereby a raw
thermoelectric semiconductor material having crystal strain can be
achieved.
[0042] In addition, the raw thermoelectric semiconductor material
has a great thickness and a large width as a result of
solidification from molten raw alloy under slow cooling rate.
Therefore, each raw thermoelectric semiconductor material may have
large volume, and therefore may have a small specific surface area
compared with a powder or the like of fine sizes. Therefore, the
possibility of surface oxidization is reduced, and thereby,
lowering of the electric conductivity of the raw thermoelectric
semiconductor material can be prevented.
[0043] In the above described method, when heating during
solidification forming of a raw thermoelectric semiconductor
material is performed by multiple step method, the layered raw
thermoelectric semiconductor material can be heated in such a
manner that the entire body reaches a desired temperature for
solidification and formation even when the heating position by the
heat source is biased during heating raw thermoelectric
semiconductor material for solidification and formation. Therefore,
the compact formed through solidification forming of a raw
thermoelectric semiconductor material can be made homogeneous
throughout the entire body, and therefore, the thermoelectric
semiconductor material manufactured by plastic deformation of the
compact can be made homogeneous throughout the entire body. In
addition, when the raw alloy is controlled to have a composition
containing excess Te, the above excess component can be dissolved
at the grain boundaries, and thus, the junction at the grain
boundaries can be improved.
[0044] In addition, when the plastic deformation process comprises
one or more omnidirectional hydrostatic pressure process, the
occurrence of buckling can be prevented and an uniform deformation
rate can be obtained during the plastic deformation of the compact.
Therefore, a texture of the thermoelectric semiconductor material
formed by the above described plastic deformation can be
homogenized.
[0045] A thermoelectric semiconductor element may be cut out from
the above described thermoelectric semiconductor material having
excellent crystalline orientation in which both the extending
direction of C face and the direction of c-axis of the hexagonal
structure of the crystal grains are uniformly oriented. When the
cut surface of thermoelectric semiconductor element include, as a
contact surface with an electrode, a plane approximately
perpendicular to the uniaxial direction of shear force application
during the plastic deformation of compact to form the
thermoelectric semiconductor material, it is possible to convey a
current or heat in the direction approximately parallel to the
extending direction of C face of the crystal grains. Therefore, the
thermoelectric performance of the thermoelectric semiconductor
element can be enhanced.
[0046] Accordingly, by a manufacturing method for a thermoelectric
semiconductor element, in which a thermoelectric semiconductor
material is cut to form a thermoelectric semiconductor element so
that an approximately perpendicular plane to the uniaxial direction
of shear force application during the plastic deformation of
compact may be used as a contact sure with an electrode, the above
described thermoelectric semiconductor element having enhanced
thermoelectric performance can be achieved.
[0047] A P type thermoelectric element and an N type thermoelectric
semiconductor element may be formed as above described
thermoelectric semiconductor elements having a high thermoelectric
performance. A PN element pair may be formed by joining, via a
metal electrode, the P type and N type thermoelectric semiconductor
elements arranged so that the elements are align in the direction
perpendicular to the axial direction of pressure application during
plastic deformation of compact for forming a thermoelectric
semiconductor material, and also perpendicular to the direction of
shear force by the pressure application. A thermoelectric
semiconductor module may be made to have the configuration provided
by the PN element pair. In such a thermoelectric semiconductor
module, a stress caused by expansion or contraction of the metal
electrode accompanied with temperature deviation during the use of
the thermoelectric module can be applied to each of the P type and
N type thermoelectric semiconductor elements in the direction
parallel to C face of the hexagonal structure of the respective
crystal grains. Therefore, even when the metal electrode expands or
contracts, interlayer peeling of the crystals in the texture of the
thermoelectric semiconductor elements can be prevented, strength
and durability of the thermoelectric module can be enhanced.
[0048] Accordingly, the thermoelectric module having enhanced
durability and strength can be achieved by a manufacturing method
for a thermoelectric module comprising: preparing P type and N type
thermoelectric semiconductor elements as above described
thermoelectric semiconductor elements; arranging the P type and N
type thermoelectric semiconductor elements so that the elements are
aligned in the direction perpendicular to the axial direction of
pressure application during plastic deformation of a compact, and
also perpendicular to the direction of shear force by the pressure
application; joining the P type and N type elements via a metal
electrode to form a PN element pair.
[0049] According to the present invention as described above,
excellent effects can be obtained as following:
[0050] (1) A thermoelectric semiconductor material is produced by:
layering and packing plate shaped raw thermoelectric semiconductor
materials made of a raw alloy having a predetermined composition of
a thermoelectric semiconductor to form a layered body; solidifying
and forming the layered body to form a compact; plastically
deforming the compact by applying pressure to the compact in a
uniaxial direction that is perpendicular or nearly perpendicular to
the main layering direction of the raw thermoelectric semiconductor
material, and thereby applying shear force in a uniaxial direction
that is approximately parallel to the main layering direction of
the raw thermoelectric semiconductor material. In such a
thermoelectric semiconductor elements, it is possible to enhance
the strength by applying additional pressure to plastically
deforming the compact which is formed by solidifyication forming of
plate shaped raw thermoelectric semiconductor materials. At the
same time, not only the extending direction of C face, but also the
direction of c-axis of the hexagonal structure in the crystal gains
in the texture can be uniformly oriented, and highly excellent
crystalline orientation can be achieved. Therefore, by setting the
direction in which current and heat are conveyed in the extending
direction of C face of the crystal grains, thermoelectric
performance can be enhanced.
[0051] (2) Accordingly, the above described thermoelectric
semiconductor material may be achieved by a manufacturing method of
a thermoelectric semiconductor material comprising: melting a raw
alloy having a predetermined composition of thermoelectric
semiconductor; subsequently having the molten alloy contacted with
the surface of a cooling member and thereby forming plate shaped
raw thermoelectric semiconductor materials; layering the plate
shaped raw thermoelectric semiconductor materials in a direction
approximately parallel to the direction of the plate thickness to
form a layered body; solidifying and forming the layered body to
form a compact; applying pressure to the compact in one of two
axial directions which are crossing each other in a plane
approximately perpendicular to the main layering direction of the
raw thermoelectric semiconductor materials, while preventing
deformation of the layered by in the other axial direction; and
thereby applying shear force in an axial direction approximately
parallel to the main layering direction of the raw thermoelectric
semiconductor materials, and plastically deforming the layered body
to form a thermoelectric semiconductor material.
[0052] (3) In a thermoelectric semiconductor material having a
compound phase comprising: complex compound semiconductor phase
having a predetermined stoichiometric composition of a compound
thermoelectric semiconductor, and a Te rich phase in which excess
Te is added to the above composition, crystal grain boundaries
exist in the thermoelectric semiconductor material, and crystal
strain is generated due to the presence of the compound phase of
complex compound semiconductor phase and the Te rich phase. By the
introduction of crystal stain, thermal conductivity can be lowered,
and therefore, the Figure-of-Merit can be increased as a result of
the lowering of thermal conductivity.
[0053] (4) In a thermoelectric semiconductor material produced by:
adding excess Te to the predetermined stoichiometric composition of
a compound thermoelectric semiconductor to form a raw alloy;
layering and packing plate shaped raw thermoelectric semiconductor
materials made of the raw alloy to form a layered body; solidifying
and forming the layered body to form a compact; applying pressure
to the compact in an axial diction perpendicular or nearly
perpendicular to the main layering direction of the raw
thermoelectric semiconductor materials; and thereby applying shear
force in an axial direction approximately parallel to the main
layering direction of the raw thermoelectric semiconductor
materials, and plastically deforming the compact, the
thermoelectric semiconductor material is provided with excellent
crystalline orientation in which both extending direction of C face
of the hexagonal structure of the crystal grains and direction of
c-axes of the crystal grains are approximately uniformly oriented.
In addition, due to the presence of the compound phase of complex
compound semiconductor phase and the Te rich phase, thermal
conductivity can be lowered, and therefore, the Figure-of-Merit can
be further increased.
[0054] (5) Accordingly, a thermoelectric semiconductor having above
described excellent crystalline orientation, a compound phase of
complex compound semiconductor phase and the Te rich phase, and a
high Figure-of-Merit can be achieved by a manufacturing method for
a thermoelectric semiconductor material, comprising controlling a
raw alloy to have a composition in which excess Te is added to the
predetermined stoichiometric composition of a compound
thermoelectric semiconductor.
[0055] (6) In the above described method, a P type thermoelectric
semiconductor material having high thermoelectric performance can
be produced by controlling the raw alloy to have a composition in
which excess Te is added to a (Bi--Sb).sub.2Te.sub.3 based
stoichiometric composition, concretely, by controlling the raw
alloy to nave a composition where 0.1% to 5% of excess Te is added
to the stoichiometric composition of a compound thermoelectric
semiconductor comprising 7 to 10 atomic % of Bi, 30 to 33 atomic %
of Sb, and 60 atomic % of Te.
[0056] (7) On the other band, a N type thermoelectric semiconductor
material having above described high thermoelectric performance can
be produced by controlling the raw alloy to have a composition
where excess Te is added to a Bi.sub.2(Te--Se).sub.3 based
stoichiometric composition, concretely, by controlling the raw
alloy to have a composition where 0.01% to 10% of excess Te is
added to the stoichiometric composition of a compound
thermoelectric semiconductor comprising 40 atomic % of Bi, 50 to 59
atomic % of Te, and 1 to 10 atomic % of Se.
[0057] (8) Furthermore, by carrying out solidification forming of
the raw thermoelectric semiconductor material by applying pressure
along with heating the raw material to a temperature no less than
380.degree. C. and no higher than 500.degree. C., the
thermoelectric semiconductor material can be solidified and formed
in a state in which the Te rich phase in the raw thermoelectric
semiconductor material is prevented from being converted to liquid
phase, or the Te rich liquid phase is controlled to be a small
amount. Therefore, a P type or N type thermoelectric semiconductor
material can be formed, having a multi phase structure of the P
type or N type complex compound semiconductor phase dispersing
microscopic Te rich phases including an excess Te in the above
semiconductor composition.
[0058] (9) Moreover, in the manufacturing method, when a molten
alloy of the raw alloy is contacted with the surface of a cooling
member to form a plate shaped raw thermoelectric semiconductor
material, the cooling rate of the molten alloy during
solidification may be controlled to a rate at which 90% or more of
the thickness of the plate shaped raw thermoelectric semiconductor
material is not quenched. Concretely, a rotational roll may be used
as the cooling member, and when the plate shaped raw thermoelectric
semiconductor material is formed by supplying the molten alloy of
the raw alloy to the surface of such cooling member, the rotational
roll may be rotated at a rate at which the thickness of the raw
thermoelectric semiconductor material is controlled to be at least
no less than 30 .mu.m. By this method, microscopic crystal nuclei
are formed on the side of contact sure of the molten raw alloy and
the cooling member, and the molten alloy can be slowly solidified
so that, from the nuclei, large crystal grains grow in the
direction of the thickness, and the raw thermoelectric
semiconductor material can be formed to have a thickness of no less
than 30 .mu.m. At that time, the crystal grains can be grown in
such a manner that C face of the hexagonal structure of the
crystals extend in the direction of thickness, approximately
throughout the entire thickness of the raw thermoelectric
semiconductor material. When the raw alloy is made to have a
composition including excess Te, in the (Bi--Sb).sub.2Te.sub.3
based P type complex compound semiconductor phase or in the
Bi.sub.2(Te--Se).sub.3 based N type complex compound semiconductor
phase, the Te rich phases including an excess Te in each of the
above compositions can be microscopically dispersed as separated
phase without being converted to amorphous phase. Thus, a Te rich
phase precipitate as hetero phase or nucleate as hetero phase
nuclei within crystal grains or in grain boundaries of the complex
compound semiconductor, and thereby a raw thermoelectric
semiconductor material having crystal strain can be achieved.
[0059] In addition, the raw thermoelectric semiconductor material
has a large thickness and a large width as a result of
solidification from molten raw alloy under slow cooling rate.
Therefore, each raw thermoelectric semiconductor material may have
large volume, and therefore may have a small specific surface area
compared with a powder or the like of fine sizes. Therefore, the
possibility of surface oxidization is reduced, and thereby,
lowering of the electric conductivity of the raw thermoelectric
semiconductor material can be prevented.
[0060] (10) In the above described method, when heating during
solidification and forming process of a raw thermoelectric
semiconductor material is performed by multiple step method, the
layered raw thermoelectric semiconductor material can be heated in
such a manner that the entire body reaches a desired temperature
for solidification forming even when the heating position by the
heat source is biased during heating raw thermoelectric
semiconductor material for solidification forming. Therefore, the
compact formed through solidification forming of a raw
thermoelectric semiconductor material can be made homogeneous
throughout the entire body, and therefore, the thermoelectric
semiconductor material manufactured by plastic deformation of the
compact can be made homogeneous throughout the entire body. In
addition, when the raw alloy is controlled to have a composition
containing excess Te, the above excess component can be dissolved
at the grain boundaries, and thus, the junction at the gain
boundaries can be improved
[0061] (11) In addition, when the plastic working process in the
method comprises one or more omnidirectional hydrostatic pressure
process, the occurrence of buckling can be prevented and an uniform
deformation rate can be obtained during the plastic deformation of
the compact. Therefore, a texture of the thermoelectric
semiconductor material formed by the above described plastic
deformation can be homogenized.
[0062] (12) A thermoelectric semiconductor element may be cut out
from the above described thermoelectric semiconductor material
having excellent crystalline orientation in which both the
extending direction of C face and the direction of c-axis of the
hexagonal structure of the crystal grains are uniformly oriented.
When the cut surface of thermoelectric semiconductor element
include, as a contact surface with an electrode, a plane
approximately perpendicular to the uniaxial direction of shear
force application during the plastic deformation of a compact to
form the thermoelectric semiconductor material, it is possible to
convey a current or heat in the direction approximately parallel to
the extending direction of C face of the crystal grains. Therefore,
the thermoelectric performance of the thermoelectric semiconductor
element can be enhanced
[0063] (13) Accordingly, the above described thermoelectric
semiconductor element having enhanced thermoelectric performance
can be achieved by a manufacturing method for a thermoelectric
semiconductor element, comprising slicing a thermoelectric
semiconductor material to form a thermoelectric semiconductor
element so that an approximately perpendicular plane to the weal
direction of shear force application during the plastic deformation
of a compact may be used as a contact surface with an
electrode.
[0064] (14) A P type thermoelectric element and an N type
thermoelectric semiconductor element may be formed as above
described thermoelectric semiconductor elements having a high the
thermoelectric performance. A PN element pair may be formed by
joining, via a metal electrode, the P type and N type
thermoelectric semiconductor elements arranged so that the elements
are aligned in the direction perpendicular to the axial direction
of pressure application during plastic deformation of a compact for
forming a thermoelectric semiconductor material, and also
perpendicular to the direction of shear force by the pressure
application. A thermoelectric semiconductor module may be made to
have the configuration provided by the above described PN element
pair. In such a thermoelectric semiconductor module, a stress
caused by expansion or contraction of the metal electrode
accompanied with temperature deviation during the use of the
thermoelectric module can be applied to each of the P type and N
type thermoelectric semiconductor elements in the direction
parallel to C face of the hexagonal structure of the respective
crystal grains. Therefore, even when the metal electrode expands or
contracts, interlayer peeling of the crystals in the texture of the
thermoelectric semiconductor elements can be prevented, strength
and durability of the thermoelectric module can be
[0065] (15) Accordingly, the thermoelectric module having enhanced
durability and strength can be achieved by a manufacturing method
for a thermoelectric module comprising: preparing P type and N type
thermoelectric semiconductor elements as above described
thermoelectric semiconductor elements; arranging the P type and N
type thermoelectric semiconductor elements so that the elements are
aligned in the direction perpendicular to the axial direction of
pressure application during plastic deformation of a compact, and
also perpendicular to the direction of shear force by the pressure
application; joining the P type and N type elements via a metal
electrode to form a PN element pair.
BRIEF DESCRIPTION OF THE DRAWINGS
[0066] FIG. 1 is a flow chart showing an embodiment of
manufacturing method for a thermoelectric semiconductor material
according to the present invention.
[0067] FIG. 2 is a diagram schematically showing a device used in
the slow cooling foil manufacturing process of FIG. 1.
[0068] FIG. 3 is a schematic perspective diagram showing a raw
thermoelectric semiconductor material formed in the slow cooling
foil manufacturing process of FIG. 1.
[0069] FIG. 4 is a graph showing the correlation between the
thickness of a raw thermoelectric semiconductor material formed in
the slow cooling foil manufacturing process of FIG. 1 and the
circumferential velocity of the cooling roll.
[0070] FIG. 5 is a graph showing the correlation between the width
of the raw thermoelectric semiconductor material formed in the slow
cooling foil manufacturing process of FIG. 1 and the
circumferential velocity of the cooling roll.
[0071] FIG. 6A is a photograph showing the cross section of the
structure of a raw thermoelectric semiconductor material formed in
the slow cooling foil manufacturing process of FIG. 1;
[0072] FIG. 6B is a photograph of the structure of a raw
thermoelectric semiconductor material formed in the slow cooling
foil manufacturing process of FIG. 1 showing a surface of the raw
thermoelectric semiconductor material opposite to the contact
surface with a rotational roll.
[0073] FIG. 7A is a schematic perspective diagram showing a compact
formed in the solidification forming process of FIG. 1.
[0074] FIG. 7B is a perspective diagram of a compact formed in a
solidification forming process of FIG. 1 schematically showing the
layered structure of a raw thermoelectric semiconductor
material.
[0075] FIG. 7C is an enlarged perspective diagram showing a partial
cross section of a compact shown in FIG. 7B.
[0076] FIG. 8A is a diagram showing a plastic working device used
in the plastically deforming process of FIG. 1 and is a schematic
cross sectional side view of the device in the initial state before
plastically deforming the compact.
[0077] FIG. 8B is a diagram showing the device of FIG. 8A as viewed
along the line A-A in the direction of the arrows;
[0078] FIG. 8C is a diagram showing a plastic working device used
in the plastically deforming process of FIG. 1 and is a schematic
cross sectional side view of the device in a state in which a
thermoelectric semiconductor material is formed by plastic
deformation of a compact.
[0079] FIG. 8D is a diagram corresponding to FIG. 8B showing
another type of the plastic working device used in the plastically
deforming process of FIG. 1 and is provided with a ring for fixing
the position.
[0080] FIG. 9A is a schematic perspective diagram showing a
thermoelectric semiconductor material formed in the plastically
deforming process of FIG. 1.
[0081] FIG. 9B is a perspective diagram schematically showing the
crystalline orientation of a thermoelectric semiconductor material
formed in the plastically deforming process of FIG. 1;
[0082] FIG. 10 is a graph showing the correlation between the
circumferential velocity of the cooling roll in the slow cooling
foil manufacturing process of FIG. 1 and the thermal conductivity
of the thermoelectric semiconductor material formed in the
plastically deforming process of FIG. 1 using a raw thermoelectric
semiconductor material formed in the slow cooling foil
manufacturing process.
[0083] FIG. 11 is a graph showing the correlation between the
circumferential velocity of the cooling roll in a slow cooling foil
manufacturing process of FIG. 1 and the electric conductivity of a
thermoelectric semiconductor material that is formed in the
plastically deforming process of FIG. 1 using a raw thermoelectric
semiconductor material formed in this slow cooling foil
manufacturing process.
[0084] FIG. 12 is a graph showing the correlation between the
circumferential velocity of the cooling roll in a slow cooling foil
manufacturing process of FIG. 1 and the Seebeck coefficient of a
thermoelectric semiconductor material formed in a plastically
deforming process of FIG. 1 using the raw thermoelectric
semiconductor material formed in the slow cooling foil
manufacturing process.
[0085] FIG. 13 is a graph showing the correlation between the
circumferential velocity of a cooling roll in a slow cooling foil
manufacturing process of FIG. 1 and the carrier concentration of
the thermoelectric semiconductor material formed in the plastically
deforming process of FIG. 1 using a raw thermoelectric
semiconductor material formed in the slow cooling foil
manufacturing process.
[0086] FIG. 14 is a graph showing the correlation between the
circumferential velocity of the cooling roll in the slow cooling
foil manufacturing process of FIG. 1 and the Figure-of-Merit of the
thermoelectric semiconductor material formed in the plastically
deforming process of FIG. 1 using the raw thermoelectric
semiconductor material formed in this slow cooling foil
manufacturing process;
[0087] FIG. 15 is a graph showing the correlation between the
thickness and the oxygen concentration of the raw thermoelectric
semiconductor material formed in a slow cooling foil manufacturing
process of FIG. 1.
[0088] FIG. 16 is a graph showing the correlation between the width
and oxygen concentration of the raw thermoelectric semiconductor
material that is formed in a slow cooling foil manufacturing
process of FIG. 1.
[0089] FIG. 17 is a graph showing the correlation between the
circumferential velocity of the cooling roll in a slow cooling foil
manufacturing process of FIG. 1 and the oxygen concentration of the
raw thermoelectric semiconductor material formed in the slow
cooling foil manufacturing process.
[0090] FIG. 18 is a graph showing the correlation between the
oxygen concentration in the raw thermoelectric semiconductor
material that is manufactured in the slow cooling foil
manufacturing process of FIG. 1 and the Figure-of-Merit of the
thermoelectric semiconductor material formed using the raw
thermoelectric semiconductor material.
[0091] FIG. 19 is a flow chart showing another embodiment of a
manufacturing method for the thermoelectric semiconductor material
according to the present invention;
[0092] FIG. 20A is a diagram showing a plastic working device used
for an omnidirectional hydrostatic pressure process of FIG. 19 and
is a schematic cross sectional side view of the device in the
initial state before the plastic deformation of a compact.
[0093] FIG. 20B is a diagram showing the device of FIG. 20A as
viewed along line B-B in the direction of the arrows.
[0094] FIG. 20C is a diagram showing the plastic working device
used for an omnidirectional hydrostatic pressure process of FIG. 19
and is a schematic cross sectional side view of the device in a
state in which omnidirectional hydrostatic pressure is applied to a
compact that has been plastically deformed by a predetermined
amount.
[0095] FIG. 21 is a schematic perspective diagram showing steps of
the manufacturing method for a thermoelectric semiconductor element
of the present invention, and showing a state for slicing a
thermoelectric semiconductor material, a sliced wafer, and a
thermoelectric semiconductor element cut out from a wafer.
[0096] FIG. 22 is a schematic perspective diagram showing an
embodiment of a thermoelectric module according to the present
invention.
[0097] FIG. 23 is a schematic perspective diagram showing a
comparative example for a thermoelectric module of FIG. 22.
[0098] FIG. 24A is a schematic cross sectional side view showing
another example of a plastic working device used in a plastically
deforming process of FIG. 1.
[0099] FIG. 24B is a diagram showing the device of FIG. 24A along
line C-C in the direction of the arrows.
[0100] FIG. 25A is a schematic diagram showing an example of the
plastically deforming process of FIG. 1 by another device, and
showing a state in which a compact is plastically deformed by a
high pressure press.
[0101] FIG. 25B is a schematic diagram showing an example of the
plastically deforming process of FIG. 1 by another device, and
showing a state in which a compact is plastically deformed by a
rolling device.
[0102] FIG. 26 is a graph showing the results of the comparison of
the thermoelectric performance of a thermoelectric module
manufactured by the manufacturing method of the present invention
with that of a thermoelectric module manufactured by another
manufacturing method.
[0103] FIG. 27 is a perspective diagram schematically showing an
example of a conventional thermoelectric module.
BEST MODE FOR CARRYING OUT THE INVENTION
[0104] In the following embodiments of the present invention are
explained with reference to the drawings.
[0105] FIGS. 1 to 18 show an embodiment of manufacturing method for
a thermoelectric semiconductor material according to the present
invention. As shown in the flow chart of FIG. 1, basically the
thermoelectric semiconductor material is manufactured by: preparing
an alloy by mixing, in a predetermined ratio, respective metals
composing a raw alloy of a thermoelectric semiconductor; melting
the metals to form a molten alloy; slowly cooling the molten alloy
by an undermentioned cooling method at a rate at which 90% or more
of the thickness of the raw thermoelectric semiconductor material
is not quenched; solidifying the molten alloy to form a thin plate
shaped foils (slow cooling foils) as raw thermoelectric
semiconductor materials; after layering and packing the slow
cooling foils produced as raw thermoelectric semiconductor
materials so that the foils are layered in a mold, in the direction
of plate thickness, solidification forming the layered foils under
an undermentioned predetermined heating condition to form a
compact; next, plastically deforming the compact by applying a load
in such a manner that a shear stress is applied in an uniaxial
direction approximately parallel to the main layering direction of
the raw thermoelectric semiconductor material, and thereby
manufacturing a thermoelectric semiconductor material.
[0106] Concrete manufacturing methods for an N type thermoelectric
semiconductor material and an N type semiconductor element are
described as follows.
[0107] Firstly, to prepare a stoichiometric composition of a raw
alloy of an N type thermoelectric semiconductor in a component
mixing process I, Bi, Se and Te are weighed so that the raw alloy
contains 40 atomic % of Bi, 1 to 10 atomic % of Se, and 50 to 59
atomic % of Te. The weighed metals are mixed to obtain a
Bi.sub.2(Te--Se).sub.3 based composition. Furthermore excess Te is
aided so that 0.01 to 10% by weight of Te is contained in the
entire Bi.sub.2(Te--Se).sub.3 based component, and thus an alloy
having a nonstoichiometric composition with excess Te is prepared.
At that time, a predetermined amount of dopant for forming an N
type thermoelectric semiconductor, such as Hg, Ag, Cu or a halogen
dopant, may be added.
[0108] Next, in a slow cooling foil manufacturing process II, as
shown in FIG. 2, a metal mixture that has been mixed and prepared
in the above-described component mixing process I is put into a
melting crucible 6 made of quartz. The crucible is introduced into
a container 5 which can hold a low oxygen concentration atmosphere
such as a reduction gas atmosphere, an inert gas atmosphere or a
vacuum. The crucible is heated by a heating coil 7 so as to melt
the metal to form a molten alloy 8. After that, the molten alloy 8
is supplied to the surface of a rotational roll 9 such as a water
cooled roll. The rotational roll act as cooling member and the
molten alloy is solidified. So as to form slow cooling foils as raw
thermoelectric semiconductor materials 10 of at least 30 .mu.m or
more in thickness, the molten alloy is supplied from a nozzle which
has a predetermined diameter, for example 0.5 mm, and is provided
at the bottom of the melting crucible 6, to the surface of the
rotational roll 9 rotating at a slow rate at which the
circumference velocity is no higher than 5 m/sec, and thereby the
molten alloy is solidified. By this process, slow cooling foils as
raw thermoelectric semiconductor materials 10 in thin plate shaped
forms arm manufactured as shown in FIG. 3.
[0109] It is preferable to set the rotational velocity of the
rotational roll 9 so that the circumferential velocity is no higher
than 2 m/sec. When the circumference velocity of the rotational
roll 9 is set to be no higher than 5 m/sec, as it is obviously
shown in the graph of FIG. 4, the thickness of the slow cooling
foil manufactured as a raw thermoelectric semiconductor material 10
can be made as thick as 30 .mu.m or more. In addition, when molten
alloy 8 is solidified on the surface of the rotational roll 9 to
form the raw thermoelectric semiconductor material 10, the molten
alloy can be solidified at a rate by which 90% or more of the
thickness of the raw thermoelectric semiconductor material is not
quenched. Therefore, as shown in FIG. 3, crystal grains 11 formed
in the texture of the raw thermoelectric semiconductor material 10
may have a length extending throughout entire thickness of the slow
cooling foil as the raw thermoelectric semiconductor material 10,
and thus, raw thermoelectric semiconductor material 10 having an
excellent crystalline orientation can be formed. Furthermore, when
the circumferential velocity of rotational roll 9 is set to be no
greater than 2 m/sec, the thickness of raw thermoelectric
semiconductor material 10 can be effectively increased to a value
of no less than approximately 70 .mu.m. Thus lengths of crystal
grains 11 can be additionally increased, and the crystalline
orientation can be further improved. In addition, as described
above, when the rotational speed of rotational roll 9 is set so
that the circumferential velocity becomes no greater than 5 m/sec,
as it is obvious from the graph shown in FIG. 5, the width of the
slow cooling foils manufactured as the raw thermoelectric
semiconductor materials 10 can be increased, and the volumes of
each raw thermoelectric semiconductor material 10 can be
increased.
[0110] Crystal grains 11 in the texture of raw thermoelectric
semiconductor material 10 are schematically illustrated as hexagons
in FIG. 3. These hexagons do not show the actual crystal lattice in
the hexagonal structure of the above-described crystal grains 11,
but for convenience in explanation, schematically show the
direction of C face of the hexagonal structure of the crystal
grains 11 by the hexagons, and in addition, by the flattened
direction of the hexagons, schematically indicate the direction in
which crystal grains 11 are flattened, that is, the direction in
which the crystal grains are oriented. This can be applied to the
following figures.
[0111] As a result of this, molten alloy 8 of the raw alloy is
supplied to the rotational roll 9 and is slowly cooled, and thereby
is slowly and sequentially cooled from the contact surface with the
rotational roll toward the outer periphery of the roll, that is in
the direction of the thickness of molten alloy 8. As a result, as
shown in FIG. 3, the crystal structures of the complex compound
semiconductor phases of Bi.sub.2Te.sub.3 and Bi.sub.2Se.sub.3 are
respectively solidified and crystallized, in which extending
direction of C face of the hexagonal structure of crystal grains 11
are mainly oriented in the direction of the plate thickness (the
direction shown by arrow t in the figure). At the same time, since
Te is added to the above molten alloy 8 so that excess Te is added
to the Bi.sub.2(Te--Se).sub.3 based stoichiometric composition, Te
rich phases including excess Te in the composition of
Bi.sub.2Te.sub.3 or Bi.sub.2Se.sub.3 are microscopically dispersed
as a non-amorphous separated phase in the crystal grains and grain
boundaries of the respective complex compound semiconductor phases
of Bi.sub.2Te.sub.3 and Bi.sub.2Se.sub.3. Thus a raw thermoelectric
semiconductor material 10 that is thought to have a structure
dispersing microscopic Te-rich phase, that is, a structure having
crystal strain by precipitation of hetero phase (Te-rich pahse) or
by nucleation of hetero pahse nuclei within crystal grains and
grain boundaries of the Bi.sub.2(Te--Se).sub.3 based complex
compound semiconductor, can be achieved.
[0112] FIGS. 6A and 6B show scanning electron microscope (SEM)
images of a texture of raw thermoelectric semiconductor material 10
manufactured by the above-described slow cooling foil mating
process II. FIG. 6A shows a cross section of the raw thermoelectric
semiconductor material 10. In this figure, contact surface with the
rotational roll 9 is placed on the upper side. FIG. 6B shows the
surface structure of the raw thermoelectric semiconductor material
10 opposite to the contact surface with the rotational roll.
[0113] As is clear from the FIG. 6A, raw thermoelectric
semiconductor materials 10 having a thickness of no less than 30
.mu.m can be formed in the slow cooling foil manufacturing process
II. The contact surface with the rotational roll 9 shows fine
crystal gains formed by quenching of molten alloy 8 by the contact
with the rotational roll 9. These fine crystal grains are formed
only in the surface region on the side of the contact surface with
the rotational roll 9, whereas other than the surface region having
the fine crystal grains, in the region of 90% or more of the
thickness, large crystal grams 11 oriented in the direction of the
plate thickness throughout the entire thickness of the plate can be
formed.
[0114] In addition, as is clear from FIG. 6B, the raw
thermoelectric semiconductor material 10 have a textual structure
in which crystal grains 11a of hetero phases (Te rich phases) are
generated within the grains and grain boundaries of crystal grains
11 of the Bi.sub.2(Te--Se).sub.3 based complex compound
semiconductor or the like, which are flattened and oriented so as
to extend in direction of the plate thickness. Powder particles of
small grain sizes mixed in the raw thermoelectric semiconductor
materials 10 manufactured by the slow cooling foil manufacturing
process II may be removed in advance by sieving, before the raw
thermoelectric semiconductor materials being sent to the following
solidification forming process III.
[0115] Next, in the solidification forming process III, the slow
cooling foils of raw thermoelectric semiconductor materials 10
manufactured by the slow cooling foil manufacturing process II are
layered in the direction approximately parallel to the direction of
the plate thickness (the direction of arrow t) and are packed in a
mold, not shown, within a container (not shown) that can hold a low
oxygen concentration atmosphere such as a reduction gas atmosphere,
an inert gas atmosphere or a vacuum of 10 Pa or less. After that,
the foils are sintered and pressurized and are solidified and
formed to have a predetermined form. For example, a rectangular
solid shaped compact 12 having a predetermined width corresponding
to a spacing between restricting members 15 in a plastic working
device 13 used in the after-mentioned plastically deforming process
IV is manufacturing as shown in FIGS. 7A, 7B, and 7C.
[0116] FIG. 7B schematically shows a layered structure of the slow
cooling foils of a raw thermoelectric semiconductor material 10 as
a basic configuration of the structure of the compact 12. FIG. 7C
shows an enlarged view of the layered structure of raw
thermoelectric semiconductor materials 10 of the FIG. 7B.
[0117] As conditions for the above-described sintering process
along with applying predetermined pressure, for example, pressure
of no less than 14.7 MPa, and heat is applied in a manner such that
the Te rich phase existing in the thermoelectric semiconductor
material manufactured in the above-described slow cooling foil
manufacturing process II is prevented from complete segregation,
formation of deferent phase, or liquid phase precipitation. Since
the Te-rich phase have a possibility to form a liquid phase at a
temperature of approximately 420.degree. C., sintering is carried
out by heating to a temperature condition of no higher than
500.degree. C., preferably no lower than 420.degree. C. and no
higher than 450.degree. C., and keeping at the temperature for
about 5 seconds to 5 minutes.
[0118] The lower limit of the temperature condition in the
sintering is no lower than 380.degree. C. This is because the
density of compact 12 does not increase when the sintering
temperature is lower than 380.degree. C.
[0119] At the time of the above-described sintering, multi step
heating is carried out so that the entirety of the object for
sintering can be approximately uniformly heated to the
predetermined sintering temperature without causing heterogeneous
temperature distribution in the object.
[0120] In the multi step heating, when an object for sintering is
heated to the predetermined sintering temperature using a
predetermined heating source, not shown, heating step is controlled
to comprise one or periods, for example, for no less than 10
seconds, of stopping heating by the heat source for a predetermined
period of time, or of temporally changing the heating by the heat
source so that the heating rate of the object of sintering is
slowed down, and thereby homogenizing the temperature of the whole
object for sintering by heat conduction during the above-described
stopping heating or slowing heating rate periods. After
homogenizing the temperature of the whole body in the process of
heating, by further heating the object for sintering, the object is
heated almost homogeneously to the final temperature, as the
sintering temperature.
[0121] Accordingly, by homogenizing the temperature of the entire
object for sintering in the process of heating, even though the
heating position by the heat source is biased, uneven temperature
distribution can be restrained when the temperature reaches the
sintering temperature. In this case, as a heating device (heating
furnace) for the sintering, conventional hot pressing, energized
hot pressing or pulse energized hot pressing may be used. In
addition, the above-described periods for stopping heating, or
slowing the heating rate are not limited to 10 seconds or higher,
but may be arbitrarily set depending on the heating ability of the
heat source, the size of the object for sintering, or the like.
[0122] The slow cooling foils as raw thermoelectric semiconductor
materials 10 formed in the above-described slow cooling foil
manufacturing process II have large widths and thicknesses, and
therefore, their layered body have a large volume and many
interstices. By layering and subsequently sintering along with
pressing the raw thermoelectric semiconductor materials 10 in the
solidification forming process III, atoms of the respective raw
thermoelectric semiconductor materials 10 migrate so as to fill in
the interstices between the raw thermoelectric semiconductor
materials 10. Together with the migration of atoms, the respective
raw thermoelectric semiconductor materials 10 are plastically
deformed so as to make contact with each other and fill in the
interstices between the raw thermoelectric semiconductor materials
10. Therefore, raw thermoelectric semiconductor materials 10 which
are made to make contact with each other through the plastic
deformation are joined to each other via the interfaces.
[0123] At that time, although the deformation of raw thermoelectric
semiconductor menials 10 slightly disarrange the orientation of C
face of crystal grains 11 that have been oriented approximately in
the direction of plate thickness of the raw thermoelectric
semiconductor material 10, that disordering does not cause a
volumetric breakdown of the whole body. Accordingly, as shown in
FIG. 7B, in the slow cooling foils of raw thermoelectric
semiconductor material 10 constructing the compact 12, the
orientation of crystal grains 11 is maintained as same as the
crystalline orientation (in the direction of arrow t) of a single
piece of raw thermoelectric semiconductor material 10 shown in FIG.
3. Therefore, it is possible to prevent the possibility of mass
breakdown of the orientation of C face of the crystal grains, which
could not be avoided in prior art, in which very fine raw
thermoelectric semiconductor materials were sintered.
[0124] In addition, in the formation of the compact 12, slow
cooling foils of raw thermoelectric semiconductor material 10
having a large thickness and large width are layered in the
direction approximately parallel to the direction of the plate
thickness, and subsequently solidified and formed. Therefore, the
interstices between the raw thermoelectric semiconductor materials
10 can be easily reduced, and it becomes possible to increase
density of the compact 12 to approximately 99.8% or higher of the
density of an ideal crystal structure of the complex compound
semiconductor of the same composition.
[0125] Furthermore, no or only little amount of Te rich phase in
the raw thermoelectric semiconductor material 10 is converted to a
liquid phase during sintering. Therefore, the compact 12 is formed
so as to maintain the teal structure of a complex compound
semiconductor phase having the composition of Bi.sub.2Te.sub.3 and
Bi.sub.2Se.sub.3 dispersing microscopic Te rich phases including
excess Te in the above-described compositions. In addition,
together with heating during the sintering process, the Te rich
phases partially occur in the interfaces between the slow cooling
foils as raw thermoelectric semiconductor materials 10.
[0126] After that, in the plastically deforming process IV, a
plastic working device 13 is prepared to comprise an air-tight
container, not shown, that can hold a low oxygen concentration
atmosphere, for example, having partial pressure of oxygen no
higher than 0.2 Pa by a reduction gas atmosphere, an inert gas
atmosphere or a vacuum. In such a container, as shown in FIGS. 8A,
8B, and 8C, a pair of restricting members 15 in plate form having
approximately parallel surfaces opposed to each other are placed
intervening a predetermined spacing at either side of a base 14.
The spacing corresponds to the width of the above-described compact
12 (dimension of the compact 12 in one axial direction of the two
axial directions crossing in a plane perpendicular to the main
layering direction of raw thermoelectric semiconductor material 10
forming the compact 12). Inner side of the restricting members 15
placed in the lateral direction, a punch 16 is placed so that it
can slide in the upward and downward directions. In addition, by a
vertical driving unit, not shown, along with being added with a
load, the punch 16 can be lowered from the upper position above the
restricting members 15 placed in the lateral direction to the lower
position inside between the restricting members 15. Heating units
are provided to predetermined positions of the base 14, restricting
members 15, and punch 16. As shown in FIG. 8A, in a state where the
punch 16 is pulled up to the upper position above the restricting
members 15, the compact 12 formed in the solidification forming
process III is placed in the center portion between the restricting
members 15 so that the longitudinal direction of this compact 12 is
vertically directed. At the same time, the compact 12 is arranged
so that the layering direction of the raw thermoelectric
semiconductor materials 10 forming the compact 12 (direction of
arrow t, same as the direction of the plate thickness of the raw
thermoelectric semiconductor material 10) is set to be parallel to
the restricting members 15 placed in the lateral direction, and
both sides of the compact in the direction of the width are placed
so as to make contact with the inner surfaces of the restricting
members 15 placed in the lateral direction. Next, along with
heating the compact 12 at a temperature that is no higher than
470.degree. C., preferably no higher than 450.degree. C. by the
heating units, pressure of a predetermined load is applied to the
compact 12 by lowering the punch 16 by the vertical driving unit as
shown in two-dot chain lines of FIG. 8A. As a result, as shown in
FIG. 8C, the compact 12 is plastically deformed so as to be
expanded in a uniaxial direction parallel to the layering direction
of raw thermoelectric semiconductor materials 10, and a
thermoelectric semiconductor material 17 of rectangular solid is
manufactured.
[0127] In the above-described plastic working device 13, when a
pressing force is applied from above to compact 12 by punch 16,
since deformation of the compact 12 in the direction of its width
is restricted by the restricting members 15 placed in the lateral
direction, deformation of the compact 12 is allowed only in the
direction parallel to the restricting members 15, that is to say,
in the layering direction of raw thermoelectric semiconductor
materials 10 (in the direction of arrows t), and therefore a shear
force is applied in a uniaxial direction parallel to the layering
direction. As a result, in the slow cooling foils of raw
thermoelectric semiconductor material 10 constructing the compact
12 before the above-described plastic deformation, interfaces of
layers are deformed and adjacent layers are integrated to each
other. Crystal grains being oriented so that C face of the
hexagonal structure extend in the direction parallel to the
direction of the plate thickness of raw thermoelectric
semiconductor materials 10 in the compact 12, are plastically
deformed to be flattened in the direction in which the shear force
is applied, and are oriented so that the cleavage planes are
perpendicular to the direction of the pressure.
[0128] Accordingly, as shown in FIG. 9A, in the texture of
thermoelectric semiconductor materiel 17 formed after the
plastically deforming of the compact 12, crystal grains are
oriented as schematically shown in FIG. 9B. The crystal grains 11
are respectively deformed so that C face of the hexagonal structure
extends in the expanding direction of the compact 12, that is to
say, in the direction parallel to the layering direction of raw
thermoelectric semiconductor materials 10 in the compact 12 before
the deformation (in the direction of arrows t). At the same time,
most of the crystal grains 11 are oriented so that the direction of
c-axes are aligned in the direction of compression (in the
direction of arrows p) in the plastically forming process. The
hexagons in FIG. 9B only indicate the orientation of the crystal
grains 11, but do not reflect the actual sizes of the crystal
grains 11.
[0129] During the plastically deformation of the compact 12 in the
plastic wowing device 13, strong outward sums is applied to the
restricting members 15 placed in the lateral direction. Therefore,
as show in FIG. 8D, a fixing position ring 15a may be provided so
as to surround the outer periphery of the restricting members 15
placed in the lateral direction. By this configuration, the stress
that is applied to the restricting members 15 placed in the lateral
direction may be endured by the fixing position ring 15a.
[0130] As described above, in the N type thermoelectric
semiconductor material 17 of the present invention, by slowly
cooling and solidifying molten raw alloy 8 using rotational roll 9,
crystal grins 11 are oriented in the direction of the plate
thickness, and made long to extending throughout entire plate
thickness, and thereby have an improved crystalline orientation. In
addition raw thermoelectric semiconductor materials 10 have a
structure in which Te rich phases are precipitated, as hetero phase
low melting point, in the crystal grains or grain boundaries. Along
with maintaining the crystalline orientation and the textual
structure comprising Bi.sub.2(Te--Se).sub.3 based complex compound
semiconductor phases dispersing the above-described Te-rich phase,
the raw thermoelectric semiconductor materials 10 are solidified
and formed to form the compact. The compact is expanded only in a
uniaxial direction approximately parallel to the direction of the
plate thickness of the raw thermoelectric semiconductor material
10, that is, the layering direction of the raw thermoelectric
semiconductor material 10. Because of the above-described
configuration, in the N type thermoelectric semiconductor material,
crystal strain is generated by the presence of the hetero phase
within crystal grains and grain boundaries, as well as by the
presence of grin boundaries. By the generation of the crystal
strain, thermal conductivity can be reduced. In addition, since the
directions of c-axes and extending directions of C face of the
hexagonal structure of the crystal grains 11 are approximately
uniformly oriented throughout the entire body of the thermoelectric
semiconductor material 17, thermoelectric performance (of which the
Figure-of-Merit is Z) can be enhanced by setting the direction for
conveying a current and heat to the extending direction of C face
of the crystal grains 11.
[0131] As shown in FIG. 4, the circumferential velocity of
rotational roll 9 is set at a rate as low as 5 m/sec, so that raw
thermoelectric semiconductor materials 10 having thickness of no
less than 30 .mu.m can be achieved. By using a rotational roll of
the above-described low speed rotation, the thermal conductivity
(.kappa.) of manufactured thermoelectric semiconductor material 17
can be increased compared to the case using raw thermoelectric
semiconductor material 10 made by the rotational roll 9 of high
rotational speed. As shown in FIG. 10, the above description is
clearly shown in the relationship, between the rotational speed of
rotational roll 9 during the manufacture of slow cooling foils as
raw thermoelectric semiconductor materials 10, and the thermal
conductivity (.kappa.) of the thermoelectric semiconductor material
17 manufactured from the raw thermoelectric semiconductor materials
10 through the above-described process.
[0132] In addition, as shown in FIG. 11, as it is clearly indicated
by the relationship between the rotational speed of rotational roll
9 during manufacturing slow cooling foils as raw thermoelectric
semiconductor materials 10 and electric conductivity (.sigma.) of
manufactured thermoelectric semiconductor material 17, by using a
rotational roll of the low rotational speed like the above
described value, electric conductivity (.sigma.) of manufactured
thermoelectric semiconductor material 17 can be increased, compared
to the case using raw thermoelectric semiconductor materials 10
produced by a rotational roll 9 of high rotational speed.
[0133] Furthermore, as shown in FIG. 12, as it is clearly indicated
from the relationship between the rotational speed of the
rotational roll 9 during manufacturing the slow cooling foils as
raw thermoelectric semiconductor materials 10 and the Seebeck
coefficient (.alpha.) of manufactured thermoelectric semiconductor
material 17, by using a rotational roll of the low rotational speed
like the above described value, the Seebeck coefficient (.alpha.)
of manufactured thermoelectric semiconductor material 17 can be
increased, compared to the case using raw thermoelectric
semiconductor materials 10 produced by a rotational roll 9 of high
rotational speed.
[0134] Moreover, as shown in FIG. 13, as it is clearly indicated
from the relationship between the rotational speed of rotational
roll during manufacturing slow cooling foils as raw thermoelectric
semiconductor materials 10 and the concentration of the carriers of
manufactured thermoelectric semiconductor material 17, by using a
rotational roll of the low rotational speed like the above
described value, the concentration of the carriers of manufactured
thermoelectric semiconductor material 17 can be increased, compared
to the case using raw thermoelectric semiconductor materials 10
produced by a rotational roll 9 of high rotational speed.
[0135] Accordingly, as shown in FIG. 14, as it is clearly indicated
from the relationship between the rotational speed of the
rotational roll 9 during manufacturing slow cooling foils as the
raw thermoelectric semiconductor materials 10 and the
Figure-of-Merit (Z) of manufactured thermoelectric semiconductor
material 17,
[0136] in the thermoelectric semiconductor material 17
manufactured, through the above-described procedures, from the raw
thermoelectric semiconductor material 10 that has been manufactured
by the rotational roll 9 of slow speed, the Figure-of-Merit (Z) is
increased compared to the case using the raw thermoelectric
semiconductor materials 10 produced by a rotational roll 9 of high
rotational speed.
[0137] Furthermore, as shown in FIG. 4, in the above-described
thermoelectric semiconductor material 17 according to the present
invention, the thickness of the slow cooling foils manufactured as
raw thermoelectric semiconductor materials 10 can be increased by
slowing the rotational speed of rotational roll 9, and thereby the
specific surface area can be reduced. As a result, as it is clear
from FIG. 15 showing a relationship between the thickness of slow
cooling foils as raw thermoelectric semiconductor materials 10 and
the oxygen concentration, measured by an infrared absorption
method, contained in the raw thermoelectric semiconductor materials
10, oxidization of raw thermoelectric semiconductor materials 10
can be restricted and the oxygen concentration in thermoelectric
semiconductor material 17 manufactured from the raw thermoelectric
semiconductor materials 10 can be reduced.
[0138] In addition, as shown in FIG. 5, the width of the slow
cooling foils manufactured as the raw thermoelectric semiconductor
materials 10 can be increased by slowing the rotational speed of
rotational roll 9, and thereby the specific surface area can be
reduced. As a result, as it is clear from FIG. 16 showing the
relationship between the width of slow cooling foils as raw
thermoelectric semiconductor materials 10, and the oxygen
concentration, measured by an infrared absorption method, contained
in the raw thermoelectric semiconductor materials 10, oxidization
of the raw thermoelectric semiconductor materials 10 can be
restricted in the same manner as described above, and the oxygen
concentration in manufactured thermoelectric semiconductor material
17 can be reduced.
[0139] Accordingly, as it is clear from FIG. 17 showing the
relationship between the rotational speed of the rotational roll 9
and the oxygen concentration in thermoelectric semiconductor
material 17, the oxygen concentration contained in manufactured
thermoelectric semiconductor material 17 can be reduced by slowing
the rotational speed of the rotational roll 9. Therefore, it is
possible to prevent lowering of the electric conductivity (.sigma.)
due to oxidation.
[0140] Therefore, as it is clear FIG. 18 showing the relationship
between the oxygen concentration in slow cooling foils as raw
thermoelectric semiconductor materials 10, and the Figure-of-Merit,
by reducing the oxygen concentration contained in manufactured
thermoelectric semiconductor material 17, the thermoelectric
performance of the thermoelectric semiconductor material 17 can be
increased.
[0141] The electric conductivity (.sigma.) and the Seebeck
coefficient (.alpha.) of the above-described manufactured N type
thermoelectric semiconductor material 17 can be controlled, by
adjusting the ratio of Te to Se in the Bi.sub.2(Te--Se).sub.3 based
composition, which is the standard for N type thermoelectric
semiconductor compositions.
[0142] FIG. 19 is a flow chart showing another embodiment of a
manufacturing method for a thermoelectric semiconductor material of
the present invention. In this embodiment, in plastically deforming
process IV during the manufacturing procedure of a thermoelectric
semiconductor material in the same manner as described above, when
a compact 12 is pressed, and a shear force is applied in a uniaxial
direction parallel to the layering direction of the slow cooling
foils of the raw thermoelectric semiconductor materials 10, so that
the compact is plastically deformed to a predetermined form, one or
more times of omnidirectional hydrostatic pressure process IV-2 may
be carried out during the process of the uniaxial shear force
applying process IV-1 for plastically deforming an object, for
example, at the time in which ratio of deformation is low. In the
omnidirectional hydrostatic pressure process IV-2, during the
plastic deformation of the compact 12, deformation of the compact
12 is temporarily restricted by contact with planes placed in the
direction of deformation, and at that state, a pressure is
continuously applied over a given period of time.
[0143] Accordingly, when the above-described omnidirectional
hydrostatic pressure process IV-2 is carried out, as shown in FIGS.
20A, 20D, and 20C, within a plastic working device 13 having
similar configuration as shown in FIGS. 8A, 8B, and 8C, a pair of
front and rear restricting members 18, each having approximately
parallel surface opposed to each other intervening a predetermined
spacing are provided at positions between restricting members 15 at
the lateral sides so as to form a configuration in which the space
between the above-described restricting members 15 placed in the
lateral direction is closed on the anteroposterior sides. When a
compact 12 formed in solidification forming process III is placed
in the center portion of the inside between the above-described
restricting members 15 placed in the lateral direction so that the
layering direction of the raw thermoelectric semiconductor
materials 10 constructing the compact 12 is parallel to the
surfaces of restricting members 15 placed in the lateral direction,
a predetermined gap is formed between the above-described compact
12 and front and rear restricting members 18 so as to provide a
space for deformation of the compact. In addition, a punch 16a
having a plane form corresponding to the space surrounded by the
above-described restricting members 15 and 18 at lateral and
anteroposterior sides, is provided so as to be moveable in the
upward and downward directions within the above-described space by
a vertical driving unit, not shown. Furthermore, heating units, not
shown, are provided at predetermined positions on base 14,
restricting members 15 and 18, and punch 16a. Along with preparing
a plastic working device 13a having above-described configuration,
a plastic working device 13 shown in FIGS. 8A, 8B, and 9C, is also
prepared.
[0144] When a plastic working process IV is carried out, firstly,
as shown in FIGS. 20A and 20B, compact 12 formed in solidification
forming process III is placed in the center portion between
restricting members 15 placed in the lateral direction in the
plastic working device 13a. After that, temperature conditions and
pressure conditions are adjusted as same as in the above-decribed
plastically deforming process IV, and punch 16a is lowered by the
vertical driving unit so that pressure is applied to the compact 12
from above by the lowering punch 16a. Then, as shown by two-dot
chain lines in FIG. 20A, since the two sides in the direction of
the width of the compact 12 are restricted by restricting members
15 placed in the lateral direction, shear force is applied in a
uniaxial anteroposterior direction approximately parallel to the
layering direction of the raw thermoelectric semiconductor
materials 10 forming the compact. As a result, the compact is
plastically deformed and flattened in the anteroposterior
direction. Thus, a uniaxial shear force applying process IV-1 is
carried out. After that, plastic deformation continues in the
anteroposterior direction, ad thereby, as shown in FIG. 20C, the
plastically deformed body of the compact 12 is made to be contacted
with the front and rear restricting members 18. In this state, when
further pressure is applied from above by the punch 16a, the
deformed body of the compact 12 is restricted by the restricting
members 15 placed in the lateral direction at two sides in the
direction of the width, and also restricted by restricting members
18 at two sides in the anteroposterior direction, and thereby
prevented from deformation. Therefore, pressure provided by the
punch 16a is applied to the deformed body of the compact 12 as
omnidirectional hydrostatic pressure. As described above, the
omnidirectional hydrostatic pressure process IV-2 is carried
out.
[0145] After that, the plastically deformed body of compact 12
which has been expanded (plastically deformed) in the
anteroposterior direction until it contacts front and rear
restricting members 18, is taken out from the plastic working
device 13a, and the plastically deformed body of the compact 12 is
placed in the center portion between restricting members 15 placed
in the lateral direction of plastic working device 13 in the same
manner as described in reference to FIGS. 8A, 8B, and 8C. After
that, punch 16 is lowered so as to press further the plastically
deformed body of the above-described compact 12 from above, and
thereby, the plastically deformed body of the compact 12 is further
expanded by applying a shear force in the anteroposterior
direction, which is an uniaxial direction approximately parallel to
the layering direction of raw thermoelectric semiconductor
materials 10 constructing the compact 12 before plastic
deformation. Thus, the uniaxial shear force applying process IV-1
is carried out, and thermoelectric semiconductor material 17 is
manufactured.
[0146] The above-described omnidirectional hydrostatic pressure
process IV-2 may be carried out two or more times. In this case a
plurality of plastic working devices 13a, in which the distance
between front and rear restricting members 18 increases step by
step, are prepared and the devices are sequentially used from the
one having smallest distance between front and rear restricting
members 18 is the smallest to the one having the largest distance
between front and rear restricting members 18. Pressure is applied
to the compact 12 formed in solidification forming process III from
above by lowering the punch 16a in the same manner as described
above, and thus, a shear force is applied in a uniaxial direction
approximately parallel to the layering direction of raw
thermoelectric semiconductor materials 10. As a result, the compact
is plastically deformed so that the amount of deformation from the
initial state sequentially increases. After that, omnidirectional
hydrostatic pressure is applied in a state in which deformation is
restricted by front and rear restricting members 18, and finally,
the compact may be plastically deformed so as to expand in the
anteroposterior direction by the plastic working device 13 not
having the front and rear restricting members 18.
[0147] In this case, by caring out the above-described
omnidirectional hydrostatic pressure process IV-2 on a compact 12
during plastic deformation in the uniaxial shear force applying
process IV-1, the density of the above-described compact 12 during
plastic deformation can be increased. Therefore, a possibility of
occurrence of buckling is prevented in the compact 12 on which the
plastically deforming process is finally cared out in the plastic
working device 13. In addition, two end portions of the compact 12
in the anteroposterior direction, which are the end portions in the
direction of plastic deformation, are pressed against front and
rear restricting members 18, and thereby, the forms of the two end
pons in the anteroposterior direction, of the compact 12 are
adjusted at a stage during plastic deformation. Thus, the
deformation rate of the compact 12 can be made uniform, and
therefore, it is possible to enhance the homogeneity of the texture
of manufactured thermoelectric semiconductor material 17.
[0148] When the omnidirectional hydrostatic pressure process IV-2
is carried out, due to the contact of the end portions of the
compact 12 in the anteroposterior direction with front and rear
restricting members 18, there is a possibility that the orientation
of C face of crystal grains 11 may be slightly disordered in the
end portions of the compact 12 in the anteroposterior direction.
Whereas, finally in plastic working device 13, a shear force is
applied in a uniaxial direction approximately parallel to the
layering direction of raw thermoelectric semiconductor material 10
constructing the compact 12 so that the compact is expanded without
restriction in the anteroposterior direction.
Therefore, it is possible to uniformly align the direction of C
face and the direction of c-axis of crystal grains 11 even in the
end portions in the anteroposterior direction of manufactured
thermoelectric semiconductor material 17.
[0149] Furthermore, in a manufacturing method for a thermoelectric
semiconductor material of the present invention, as shown in FIG.
19, a stress stain processing process V is provided as the process
after the above-described plastically deforming process IV. In the
stress strain processing process V, the thermoelectric
semiconductor material 17, manufactured and plastically deformed
into a predetermined form in plastically deforming process IV may
be maintained at a predetermined temperature, for example at a
temperature from 350.degree. C. to 500.degree. C., for a
predetermined period of time, for example, for 30 minutes to 24
hours so that dislocations or vacancies of crystal lattice are
reduced or reconstructed as a result of heat treatment. As a
result, stress strain which is generated as a result of the plastic
deformation in the plastically deforming process IV and remains in
the structure of thermoelectric semiconductor material 17 may be
eliminated. It is clear that the same effects can be obtained in
the stress strain processing process V even when the temperature
condition is maintained for 24 hours or more.
[0150] Moreover, a defect concentration controlling process VII may
be provided as the process after the above-described stress strain
processing process VI. By holding the thermoelectric semiconductor
material 17, from which residual stress strain has been removed in
the above-described stress strain processing process VI, at a
predetermined temperature for a predetermined period of time in the
defect concentration controlling process VII, the concentration of
defects in the thermoelectric semiconductor material 17 may be
changed, and therefore, the electric conductivity (.sigma.) and the
Seebeck coefficient (.alpha.) may be controlled.
[0151] The thermoelectric semiconductor material 17 manufactured in
the plastically deforming process IV retains a stricture of raw
thermoelectric semiconductor materials 10 constructing the compact
12, namely Bi.sub.2(Te--Se).sub.3 based complex compound
semiconductor including hetero phases (Te rich phases) in the
crystal grains or in the grain boundaries. Since the excess Te is a
component of the Bi.sub.2(Te--Se).sub.3 based thermoelectric
semiconductor, when the above-described thermoelectric
semiconductor material 17 is heat treated, the excess Te reacts
with the main component of Bi.sub.2(Te--Se).sub.3 based
semiconductor, and fill in the defects of the main component. When
a slight amount of dopant such as Ag is introduced in the main
component, performance changes largely. Such dopant has a large
influence even when it is distributed in the grain boundaries.
Performance may change largely, if the dopant diffuse into the main
component portion by the use at a high temperature or by a heat
treatment. It is considered that the change in the concentration of
defects in thermoelectric semiconductor material 17 due to the
excess Te can provide effects which cancel or accelerate the
effects of the dopant.
[0152] Next, as manufacturing method for a thermoelectric
semiconductor element according to the present invention, a case in
which N type thermoelectric semiconductor element 3a is
manufactured using N type thermoelectric semiconductor material 17
manufactured in accordance with the embodiments shown in FIGS. 1 to
18 is described in the following.
[0153] In this case, in the N type thermoelectric semiconductor
material 17, the extending direction of C face and the direction of
c-axis of the hexagonal structure of crystal grains 11 are
uniformly aligned throughout the entire structure. Therefore,
considering the orientation of crystal grains 11 having uniform
orientation, thermoelectric semiconductor element 3a is formed by
being cut out from the material, so that the direction in which a
current and heat are conveyed can be set in the extending direction
of C face in the hexagonal structure of crystal 11.
[0154] In the N type thermoelectric semiconductor material 17, as
shown in FIG. 9B, C face of the hexagonal structure in each crystal
grain extends in the direction of expansion of the compact 12
during plastic deformation (direction of arrow t), and c-axis is
oriented approximately in the direction of pressure (direction of
arrow p) during the plastic deformation. Therefore, first as shown
in the upper portion of FIG. 21, at predetermined spacing position
in the direction of expansion of the compact 12 during the plastic
deformation (direction of arrow t), the thermoelectric
semiconductor material 17 is sliced along a plane perpendicular to
the direction of expansion, and a wafer 19 is cut out, as shown in
the middle of FIG. 21.
[0155] As a result, C face of the hexagonal structure of crystal
grains 11 is oriented in the direction of the thickness of the
above-described wafer 19.
[0156] Next, a conductive material processed surfaces 20 are formed
by processing the both ends of the wafer 19, for example, by a
plating process by a plating device, not shown. Subsequently, as
shown by two-dot chain lines in the middle portion of FIG. 21, the
wafer 19 processed with conductive material is cut along two
planes: a plane perpendicular to the direction (direction of arrow
p) in which compact 12 is pressed during the manufacture of the
thermoelectric semiconductor material 17; and a plane defined by
two axes of the direction of pressing (direction of arrow p) and
the direction of expansion (direction of arrow t) during the
manufacture of the thermoelectric semiconductor material 17. Thus,
a rectangular solid form, as shown in the lower portion of FIG. 21
is cut out (diced), and thereby the N type thermoelectric
semiconductor element 3a is manufactured.
[0157] As a result, the above-described N type thermoelectric
semiconductor element 3a has a crystal structure in which, as shown
in the lower portion of FIG. 21, C face of the hexagonal structure
of crystal grains 11 extends throughout long length in the
direction (as shown by arrow t in the figure, the same direction as
the direction of expansion of the thermoelectric semiconductor
material 17 during the manufacture) of a pair of opposing surfaces
20 which are processed with a conductive material. The pair of the
surface 20 correspond to conductive material processed surfaces 20
of the wafer 19 processed with a conductive material. In addition,
c-axes of crystal grains 11 extend in the direction of pressing
(direction of arrow p in the figure) during the manufacture of the
thermoelectric semiconductor material 17 among the two axial
directions perpendicular to the conductive material processed
surface 20.
[0158] Accordingly, by attaching a metal electrode (not shown) to
the above-described conductive material processed surface 20, an N
type thermoelectric semiconductor element 3a having excellent
thermoelectric performance can be obtained, by making the element
to have a textual structure in which the direction of c-axis, as
well as the direction of C face of the hexagonal structure of the
crystal grains 11 are uniformly oriented, and allowing the current
and heat to be applied in the direction of C face of the hexagonal
structure of the above-described crystal grains 11.
[0159] Next, a case in which a P type thermoelectric semiconductor
material is manufactured is described. In this case, to prepare a
stoichiometric composition of a raw alloy of an P type
thermoelectric semiconductor in a component mixing process I shown
in FIG. 1, Bi, Sb and Te are weighed so that the raw alloy contains
7 to 10 atomic % of Bi, 30 to 33 atomic % of Sb, and 60 atomic % of
Te. The weighed metals are mixed to obtain a (Bi--Se).sub.2
Te.sub.3 based composition. Furthermore an excess Te is aided so
that 0.1 to 5% by weight of Te is contained in the entire
(Bi--Se).sub.2 Te.sub.3 based component, and thus an alloy having
excess Te is prepared. At that time, a predetermined amount of
dopant for forming a P type thermoelectric semiconductor, such as
Ag or Pb may be added.
[0160] Subsequently, in the same manner as in the case for
manufacturing above-described N type thermoelectric semiconductor
material 17, in slow cooling foil manufacturing process II using a
device shown in FIG. 2, molten alloy 8 of the metal mixture that
has been mixed in the above-described component preparing process I
is supplied from a nozzle of melting crucible 6, having a diameter
of 0.5 mm to a surface of rotational roll 9 slowly rotating at a
circumferential velocity of 5 m/sec or less, preferably at a
circumferential velocity of 2 m/sec or less, so as to be slowly
cooled and solidified, and thereby, plate shaped raw thermoelectric
semiconductor materials 10 (slow cooling foil) are
manufactured.
[0161] The circumferential velocity of rotational roll 9 is set at
5 m/sec or less, preferably 2 m/sec or less. By using such
velocity, in the same manner as in the case for forming the N type
raw thermoelectric semiconductor material 10, the slow cooling
foils are manufactured to have a thick thickness of 30 .mu.m or
more, preferably, the slow cooling foils are formed to have a
thickness of no less than 70 .mu.m, and thereby, raw thermoelectric
semiconductor materials 10 having an excellent crystalline
orientation and large crystal grains 11 extending throughout almost
entire plate thickness can be obtained. At the same time, the
widths of the slow cooling foils manufactured as raw thermoelectric
semiconductor material 10, are increased, the volume of a single
piece of the raw thermoelectric semiconductor material 10 is
increased, and thereby the specific surface area of the piece can
be reduced.
[0162] As a result, in the same manner as the above-described N
type raw thermoelectric semiconductor material 10, when the P type
raw thermoelectric semiconductor material 10 is cooled on
rotational roll 9, the crystal structures of the complex compound
semiconductor phases of Bi.sub.2Te.sub.3 and Sb.sub.2Te.sub.3 are
respectively solidified and crystallized, in which crystalline
orientation is aligned in the direction of the plate thickness. At
the same time, Te rich phases including excess Te in the
composition of Bi.sub.2Te.sub.3 or Sb.sub.2Te.sub.3 are
microscopically dispersed as a non-amorphous separated phase in the
crystal grains and grain boundaries of the Hive complex compound
semiconductor phases of Bi.sub.2Te.sub.3 and Sb.sub.2Te.sub.3. Thus
a raw thermoelectric semiconductor material 10 that is thought to
have a structure having crystal strain by precipitation of hetero
phase (Te-rich phase) or by nucleation of hetero phase nuclei
within crystal grains and grain boundaries of the
(Bi--Sb).sub.2Te.sub.3 based complex compound semiconductor, can be
achieved. In this raw thermoelectric semiconductor material 10, in
the same manner as that shown in FIG. 3, crystal grains 11 extend
in approximately the direction of the plate thickness, and the
crystal grains have a length almost corresponding to the plate
thickness. Powder particles may be removed in advance by sieving
from the raw thermoelectric semiconductor materials, before the
following solidification forming process III.
[0163] Subsequently, in solidification forming process III, slow
cooling foils of P type raw thermoelectric semiconductor materials
10 manufactured in the slow cooling foil manufacturing process II,
are layered in the direction approximately parallel to the
direction of the plate thickness, and are packed in a mold, not
shown. After that, the layered body is sintered under the same
pressure and temperature conditions by a multistage heating method
in the same manner as the manufacturing process of compact 12
having the N type composition. As a result, the layered raw
thermoelectric semiconductor materials 10 are plastically worked,
solidified and formed so that the respective pieces of raw
thermoelectric semiconductor materials 10 are made to make contact
with each other and the interstices between the raw thermoelectric
semiconductor materials are eliminated. Thus, a compact 12 in
rectangular solid form in the same manner as those shown in FIGS.
7A, 7B, and 7C is manufactured.
[0164] As a result, no or only little limited amount of Te rich
phases which have been formed in the P type raw thermoelectric
semiconductor material 10 are converted to liquid phases during
sintering. Therefore, the compact 12 is formed maintain a structure
comprising complex compound semiconductor phases having the
composition of Bi.sub.2Te.sub.3 and Sb.sub.2Te.sub.3
microscopically dispersing Te rich phases containing excess Te in
the above-described compositions.
[0165] Subsequently, in a plastically deforming process IV, in the
same manner as in the case for manufacturing the N type
thermoelectric semiconductor material 17, using a plastic working
device 13 as shown in FIGS. 8A, 8B, 8C, and 8D, along with hating
the compact 12 at a temperature no higher than 500.degree. C.,
preferably, no higher than 350.degree. C., the compact is
plastically deformed so as to expand in a uniaxial direction
approximately parallel to the layering direction of the raw
thermoelectric semiconductor materials 10, and thereby, P type
thermoelectric semiconductor material 17 is manufactured. The
above-described temperature condition for heating is varied
depending on the excessive amount of Te, and the processing
temperate is increased with decreasing amount of excess Te.
[0166] As a result, by applying shear force only in the layering
direction of raw thermoelectric semiconductor materials 10, in the
same manner as those shown in FIGS. 9A and 9B, crystal grains 11
oriented in the direction of the plate thickness of the raw
thermoelectric semiconductor material 10 in the compact 12 are
plastically deformed so as to be flatted in the uniaxial direction
in which the shear force is applied. In addition, the cleavage
planes are oriented so as to be approximately perpendicular to the
direction in which pressure is applied, and the compact is deformed
so that C face of the hexagonal structure of each crystal grain 11
is extended in the direction of expansion (direction of arrow t in
FIGS. 9A and 9B). At the same time, a P type thermoelectric
semiconductor material 17 in which c-axes of most of crystal grains
11 are oriented in the direction of compression (direction of arrow
p in FIGS. 9A and 9B) during the plastic deformation is formed.
[0167] Accordingly, in the P type thermoelectric semiconductor
material 17, crystal strain is generated by the presence of the
hetero phase within crystal grains and grain boundaries, as well as
by the presence of grain boundaries. By the generation of the
crystal strain, thermal conductivity (1c) can be reduced. In
addition, since the directions of c-axes and extending directions
of C face of the hexagonal structure of the crystal grains 11 are
approximately uniformly oriented, thermoelectric performance (of
which the Figure-of-Merit is Z) can be enhanced by setting the
direction for conveying a current and heat to the extending
direction of C face of the crystal grains 11.
[0168] Moreover, since the P type raw thermoelectric semiconductor
material 10 is manufactured to have a large thickness and a large
width, and therefore, have a small specific surface area, and is
solidified and formed to manufacture P type thermoelectric
semiconductor material 17, the oxygen concentration contained in
the thermoelectric semiconductor material 17 can be reduced. Thus,
a reduction in the electric conductivity (.sigma.) due to oxidation
can be prevented. By this reduction, an the thermoelectric
performance of thermoelectric semiconductor material 17 can also be
improved.
[0169] The electric conductivity (.sigma.) and the Seebeck
coefficient (.alpha.) of the P type thermoelectric semiconductor
material 17 can be controlled by adjusting the amounts of Bi and Sb
in the (Bi--Sb).sub.2Te.sub.3 based composition, which is the
standard of the composition of P type semiconductors. In addition,
during the manufacturing process of the P type thermoelectric
semiconductor material 17, omnidirectional hydrostatic pressure
process IV-2 in plastically deforming process IV shown in FIG. 19
may be carried out. In addition, stress stain processing process V
and defect concentration controlling process VI may be carried out
as a post process of the plastically deforming process IV.
[0170] Next, a case in which P type thermoelectric semiconductor
element 2a is manufactured using the P type thermoelectric
semiconductor material 17 manufactured by the above-described
method is described.
[0171] In this case, also in the above-described P type
thermoelectric semiconductor material 17, in the same manner as N
type thermoelectric semiconductor material 17 shown in FIGS. 9A and
9B, throughout entire textual structure, C face of the hexagonal
structure of most of crystal grains 11 extend in the direction of
expansion of the compact 12 during the plastic deformation
(direction of arrow t in FIGS. 9A and 9B), and the c-axes are
almost oriented in the direction of the pressure during the plastic
deformation (direction of arrow p in FIGS. 9A and 9B). Therefore,
in the same manner as in manufacturing method for N type
thermoelectric semiconductor element 3a shown in FIG. 21, firstly,
as shown in the upper portion of FIG. 21, at predetermined spacing
position in the direction of expansion of the compact 12 during the
plastic deformation (direction of arrow t), the thermoelectric
semiconductor material 17 is sliced along a plane perpendicular to
the direction of expansion, and thereby a wafer 19 is cut out, as
shown in the middle of FIG. 21. After that conductive material
processed surfaces 20 are formed by processing both end surfaces in
the direction of thickness of the wafer 19 with conductive
material. Subsequently, by cutting the wafer 19, a P type
thermoelectric semiconductor element 2a of a rectangular solid form
can be manufactured in the same manner as the N type thermoelectric
semiconductor element 3a shown in the lower portion of FIG. 21.
[0172] As a result, the P type thermoelectric semiconductor element
2a has, in the same manner as the above-described N type
thermoelectric semiconductor element 3a, a crystal structure in
which C face of the hexagonal structure of crystal grains 11
extends throughout long length in the direction of a pair of
opposing surface 20 which are processed with a conductive material.
In addition, c-axes of crystal grains 11 extend in the direction of
pressing (direction of arrow p) during the manufacture of the
thermoelectric semiconductor material 17 among the two axial
directions perpendicular to the conductive material processed
surface 20. Therefore the P type thermoelectric semiconductor
element has an excellent thermoelectric performance.
[0173] As another embodiment of the present invention, a
thermoelectric module that uses P type and N type thermoelectric
semiconductor elements 2a and 3a that have been manufacture in
accordance with the above-described method of the present
invention, and manufacturing method of the thermoelectric module
are described.
[0174] FIG. 22 shows thermoelectric module 1a of the present
invention, which comprises a PN element pair as in the same manner
as a conventional thermoelectric module 1 shown in FIG. 27. In the
formation of the PN element pair, the P type thermoelectric
semiconductor element 2a and N type thermoelectric semiconductor
element 3a respectively manufactured by the method of the present
invention are arranged so that the elements are aligned in the
direction perpendicular both to the extending direction of C face
and the direction of c-axis of hexagonal structure of the crystal
grains 11. Conductive material processed surfaces of the
thermoelectric semiconductor elements 2a and 3a opposed to each
other in the extending direction of C face of the crystal grains
are joined via a metal electrode 4.
[0175] As a result, in the above-described thermoelectric module 1a
of the present invention, current and heat can be conveyed in the
extending direction of C face of the crystal grains 11 of the P
type thermoelectric semiconductor element 2a and N type
thermoelectric semiconductor element 3a, in which the extending
direction of C face and the direction of c-axis of crystal gains 11
are approximately uniformly oriented. Therefore, thermoelectric
module 1a having an excellent thermoelectric performance can be
achieved.
[0176] In addition, when thermoelectric cooling, thermoelectric
heating, thermoelectric power generation, and the like are carried
out using the above-described thermoelectric module 1a, expansion
or contraction of the metal electrode 4 accompany temperature
deviation. Therefore, to adjacent P type and N type thermoelectric
semiconductor elements 2a and 3a joined via a metal electrode 4,
stress is applied in the direction in which the elements come close
to each other, or move away from each other. While in the
above-described thermoelectric module, when a PN element pair is
formed as shown in FIG. 22, adjacent thermoelectric semiconductor
elements 2a and 3a joined via a metal electrode 4 are arranged in
the same plane as the direction of C face of crystal grains 11.
Terefore, stress caused by expansion or contraction of the metal
electrode 4 can be applied to respective crystal grains 11 only in
the direction parallel to C plan. Accordingly, even when the stress
is applied, interlayer peeling of the crystal grains 11 in the
hexagonal structure in the respective structures of thermoelectric
semiconductor elements 2a and 3a can be prevented, and thus, the
damage to the thermoelectric semiconductor elements 2a and 3a due
to cleavage can be prevented, and therefore, strength and
durability of the them thermoelectric module 1a can be enhanced.
When a PN elemental pair is formed, as a comparative example as
shown in FIG. 23, by aligning the P type and N type thermoelectric
semiconductor elements 2a and 3a in the direction of c-axis in the
hexagonal structure of crystal grains 11; and joining respective
thermoelectric semiconductor elements 2a and 3a via metal electrode
4, the caused by expanding or contracting deformation of the metal
electrode 4 due to thermal deviation is applied respectively to the
thermoelectric semiconductor elements 2a and 3a in the direction of
c-axes of crystal grains 11. Accordingly, the stress works to peel
the layers in the hexagonal structure of these crystal grains 11.
In such a case, the damage to thermoelectric semiconductor elements
2a and 3a due to cleavage may be easily occur. Such occurrence of
damage can be prevented in the above-described thermoelectric
module 1a of the present invention.
[0177] The present invention is not limited only to the
above-described embodiments. In the solidification forming process
III in the manufacturing method for a thermoelectric semiconductor
material, the above description shows a processing condition for
solidifying and forming (sintering) the raw thermoelectric
semiconductor material 10 at a temperature no lower than
380.degree. C. and no higher than 500.degree. C., preferably, a no
lower than 420.degree. C. and no higher than 450.degree. C., is
maintained for 5 seconds to 5 minutes. While, it is also possible
to sinter raw thermoelectric semiconductor materials 10 for a long
period of time at a temperature no higher than 400.degree. C.
[0178] When temperature conditions and heating time may be set so
that segregation, dropping of separated phase, and liquid phase
precipitation, or the like of the Te rich phases having a low
melting point and are dispersed in complex compound semiconductor
phases do not completely occur, it is possible to form a compact 12
through plastic deformation by applying pressure, rolling, or by
extrusion. As a plastically processing device 13 used in
plastically deforming process TV, a structure having a punch 16
which can be raised and lowered inside between restricting members
15 placed in the lateral direction is described. In this case, the
compact 12 is placed in the middle portion inside the restricting
members 15 placed in the lateral direction, and this compact 12 is
pressed from above by punch 16, and thereby, the above-described
compact 12 is expanded toward the two anteroposterior sides in a
uniaxial direction parallel to the layering direction of raw
thermoelectric semiconductor material 10. While, as shown in FIGS.
24A and 24B, the plastically working device 13 may have a
configuration in which an additional restricting member 15b is
provided in a position on one side of the base 14 between
restricting members 15 placed in the lateral direction to restrict
the deformation (expansion) of compact 12 in forward and backward
direction in one direction. In this case, when compact 12 is
plastically deformed, compact 12 is firstly placed so as to be
contacted with the restricting members 15 placed in the lateral
direction and the restricting member 15b. Subsequently, the compact
12 is pressed from above by punch 16 as shown by two-dot chain
lines in the upper portion of FIG. 21. As a result, the compact 12
is expanded only in one direction opposite to the restricting
member 15b. Plastically working device 13a used in omnidirectional
hydrostatic pressure process IV-2 shown in FIGS. 20A, 20B, and 20C
may be provided with a fixing position ring 15a same as that shown
in FIG. 8D, on the outer periphery of restricting members 15 placed
in the lateral direction and front and rear restricting members 18.
In this case, during the plastic deformation of the compact 12,
stress applied in the direction to the outside of the
above-described restricting members 15 and 18 is received by the
fixing position ring. When omnidirectional hydrostatic pressure
process IV-2 is carried out two or more times, instead of preparing
a plurality of plastically working device 13a having different
spacing between front and rear restricting members 18, it is also
possible to use a plastic working device 13a in which positions of
front and rear restricting members 18 may be set to have selective
spacing. While a composition of raw alloy for thermoelectric
semiconductors is, in either case of P type or N type, described to
have excess Te added to stoichiometric composition of the
thermoelectric semiconductor complex compound, it is also possible
to add as excess composition, any element selected from Bi, Se, and
Sb element instead of Te to the stoichiometric composition of the
thermoelectric semiconductor complex compound. A manufacturing
method for a thermoelectric semiconductor material, a
thermoelectric semiconductor element, and a thermoelectric module
according to the present invention may be applied to the raw alloy
having the stoichiometric composition of the thermoelectric
semiconductor complex compound to which an excess Te is not added.
In this case, improvement of thermoelectric performance can be
expected due to an improvement of orientation of crystal grains 11
in the texture of thermoelectric semiconductor material 17. While
Bi.sub.2(Te--Se).sub.3 based, three element based composition was
described as a stoichiometric composition of raw alloy for N type
thermoelectric semiconductor, it is also possible to apply a
manufacturing method for a thermoelectric semiconductor material, a
thermoelectric semiconductor element, or a thermoelectric module to
a raw alloy having a Bi.sub.2Te.sub.3 based, two element based,
stoichiometric composition or a four element based stoichiometric
composition comprising (Bi--Sb).sub.2Te.sub.3 based composition
added with small amount of Se. While (Bi--Sb).sub.2Te.sub.3 based,
three element based composition was described as a stoichiometric
composition of P type thermoelectric semiconductor complex
compound, it is also possible to apply a manufacturing method for a
thermoelectric semiconductor material, a thermoelectric
semiconductor element, or a thermoelectric module to a raw alloy
having a four element based stoichiometric composition comprising
Bi.sub.2(Te--Se).sub.3 based composition added with small amount of
Sb. In the above description, plastically working device 13 and 13a
are used when a thermoelectric semiconductor material 17 is
manufactured through plastic deformation by applying a shear force
to a compact 12 in which slow cooling foils of raw thermoelectric
semiconductor materials 10 are layered in the direction of the
plate thickness and are solidified and formed, in a uniaxial
direction approximately parallel to the layering direction of the
above-described thermoelectric semiconductor element 10. A high
pressure pressing device 21 with a pair of dies 22 that are
moveable in the direction in which they come close to each other or
they move away from each other as shown in FIG. 25A, or a rolling
device 23 provide with a roller 24 as shown in FIG. 25B may be used
to press the compact 12 in a uniaxial direction perpendicular to
the layering direction while moving the compact in the main
layering don of raw thermoelectric semiconductor materials 10. In
this case, since a friction is applied in the direction
perpendicular to both the layering direction of the raw
thermoelectric semiconductor material 10 and the direction of
pressure application, the compact is not spread or even if it
spreads, amount of deformation is limited to small value.
Therefore, restricting members are not specifically required. Of
course, a variety of modifications can be applied to the
embodiments within the scope that does not deviate from the gist of
the present invention.
EXAMPLE
[0179] A thermoelectric module 1a was manufactured by forming a PN
element pair of P type and N type thermoelectric semiconductor
elements 2a and 3a manufactured by a manufacturing method for a
thermoelectric semiconductor element of the present invention. The
thermoelectric performance of the module was compared with that of
a thermoelectric module manufactured in accordance with another
method.
[0180] As a result, the Figure-of-Merit, shown by solid circle
.circle-solid. and open circle o in FIG. 26, were obtained as the
thermoelectric performance of thermoelectric module 1a manufactured
in accordance with the present invention.
[0181] The result indicates, it was found that high thermoelectric
performance is gained according to the invention.
[0182] As a result, thermoelectric module of the present invention
indicates high thermoelectric performance in comparison with a case
in which a P type thermoelectric semiconductor element and an N
type thermoelectric semiconductor element are both manufactured
only by conventional hot pressing of a raw thermoelectric
semiconductor material according (shown by open triangle A in FIG.
26), and a case in which N type thermoelectric semiconductor
element 2a is manufactured by a manufacturing method for a
thermoelectric semiconductor element of the present invention,
while a P type thermoelectric semiconductor element is manufactured
only by hot pressing of a raw thermoelectric semiconductor material
(shown by open diamond .diamond. and solid diamond .diamond-solid.
in FIG. 26).
* * * * *