U.S. patent application number 09/797595 was filed with the patent office on 2002-01-31 for oxide ion conductor, manufacturing method therefor, and fuel cell using the same.
This patent application is currently assigned to MITSUBISHI MATERIALS CORPORATION. Invention is credited to Adachi, Kazunori, Kuroda, Kiyoshi, Tamo, Yoshitaka, Yamada, Takashi.
Application Number | 20020013214 09/797595 |
Document ID | / |
Family ID | 26587537 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020013214 |
Kind Code |
A1 |
Kuroda, Kiyoshi ; et
al. |
January 31, 2002 |
Oxide ion conductor, manufacturing method therefor, and fuel cell
using the same
Abstract
An oxide ion conductor is manufactured having a relatively high
mechanical strength while the ionic conduction thereof is
maintained at a satisfactory level. The oxide ion conductor is
represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d.
In the oxide ion conductor, Ln1 is at least one element selected
from the group consisting of La, Ce, Pr, Nd, and Sm, A is at least
one element selected from the group consisting of Sr, Ca, and Ba,
B1 is at least one element selected from the group consisting of
Mg, Al, and In, B2 is at least one element selected from the group
consisting of Co, Fe, Ni, and Cu, and B3 is at least one element
selected from the group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn,
Mn, and Zr, wherein x is 0.05 to 0.3, y is 0.025 to 0.29, z is 0.01
to 0.15, w is 0.01 to 0.15, y+z+w is 0.035 to 0.3, and d is 0.04 to
0.3.
Inventors: |
Kuroda, Kiyoshi; (Omiya-shi,
JP) ; Yamada, Takashi; (Omiya-shi, JP) ; Tamo,
Yoshitaka; (Omiya-shi, JP) ; Adachi, Kazunori;
(Omiya-shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
MITSUBISHI MATERIALS
CORPORATION
1-5-1, Ohtemachi Chiyoda-ku
Tokyo
JP
|
Family ID: |
26587537 |
Appl. No.: |
09/797595 |
Filed: |
March 5, 2001 |
Current U.S.
Class: |
501/152 ;
205/784; 429/304; 429/320; 429/410; 429/496; 501/126 |
Current CPC
Class: |
B01D 53/326 20130101;
C04B 35/50 20130101; G01N 27/4073 20130101; Y02P 70/56 20151101;
C04B 35/01 20130101; Y02P 70/50 20151101; Y02E 60/50 20130101; Y02E
60/525 20130101; H01M 8/1246 20130101 |
Class at
Publication: |
501/152 ;
429/320; 429/304; 429/33; 205/784; 501/126 |
International
Class: |
H01M 008/12; G01N
027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2000 |
JP |
2000-071759 |
Jul 14, 2000 |
JP |
2000-213659 |
Claims
What is claimed is:
1. An oxide ion conductor represented by the formula Ln1AGaB1B2B3O,
wherein Ln1 is at least one element selected from the group
consisting of La, Ce, Pr, Nd, and Sm, the content thereof being
43.6 to 51.2 percent by weight, A is at least one element selected
from the group consisting of Sr, Ca, and Ba, the content thereof
being 5.4 to 11.1 percent by weight, the content of Ga is 20.0 to
23.9 percent by weight, B1 is at least one element selected from
the group consisting of Mg, Al, and In, B2 is at least one element
selected from the group consisting of Co, Fe, Ni, and Cu, B3 is at
least one element selected from the group consisting of Al, Mg, Co,
Ni, Fe, Cu, Zn, Mn, and Zr, wherein, in the case in which B3 is an
element differing from B1 or B2, the content of B1 is 1.21 to 1.76
percent by weight, the content of B2 is 0.84 to 1.26 percent by
weight, and the content of B3 is 0.23 to 3.08 percent by weight,
and in the case in which B3 is an element equal to B1 or B2, the
total content of B1 and B3 is 1.41 to 2.70 percent by weight, and
the total content of B2 and B3 is 1.07 to 2.10 percent by
weight.
2. An oxide ion conductor according to claim 1, wherein first
crystal grains composed of elements Ln1, A, and Ga and second
crystal grains composed of element B1 are present between matrix
crystal grains other than the first crystal grains and the second
crystal grains.
3. An oxide ion conductor according to claim 1, wherein first
crystal grains composed of elements Ln1, A, and Ga and second
crystal grains composed of element B1 are present in the matrix
crystal grains other than the first crystal grains and the second
crystal grains.
4. An oxide ion conductor according to one of claims 2 and 3,
wherein the grain diameters of the first crystal grains and the
second crystal grains are 0.1 to 2.0 .mu.m.
5. An oxide ion conductor according to one of claims 2 and 3,
wherein the grain diameter of the matrix crystal grains is 2.0 to
7.0 .mu.m.
6. An oxide ion conductor represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d,
wherein Ln1 is at least one element selected from the group
consisting of La, Ce, Pr, Nd, and Sm, A is at least one element
selected from the group consisting of Sr, Ca, and Ba, B1 is at
least one element selected from the group consisting of Mg, Al, and
In, B2 is at least one element selected from the group consisting
of Co, Fe, Ni, and Cu, B3 is at least one element selected from the
group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn, Mn, and Zr, and x
is 0.05 to 0.3, y is 0.025 to 0.29, z is 0.01 to 0.15, w is 0.01 to
0.15, y+z+w is 0.035 to 0.3, and d is 0.04 to 0.3.
7. An oxide ion conductor according to claim 6, wherein first
crystal grains composed of elements Ln1, A, and Ga and second
crystal grains composed of element B1 are present between matrix
crystal grains other than the first crystal grains and the second
crystal grains.
8. An oxide ion conductor according to claim 6, wherein first
crystal grains composed of elements Ln1, A, and Ga and second
crystal grains composed of element B1 are present in the matrix
crystal grains other than the first crystal grains and the second
crystal grains.
9. An oxide ion conductor according to one of claims 7 and 8,
wherein the grain diameters of the first crystal grains and the
second crystal grains are 0.1 to 2.0 .mu.m.
10. An oxide ion conductor according to one of claims 7 and 8,
wherein the grain diameter of the matrix crystal grains is 2.0 to
7.0 .mu.m.
11. A method for manufacturing an oxide ion conductor, comprising:
a step of mixing individual powdered oxides composed of Ln1, A, Ga,
B1, and B2 in ratios in accordance with those described in claim 1
so as to form a first powdered mixture; a step of calcining the
first powdered mixture at 500 to 1,300.degree. C. for 1 to 10 hours
so as to form calcined powder; a step of mixing a powdered oxide
composed of B3 in a ratio in accordance with that described in
claim 1 with the calcined powder so as to form a second powdered
mixture; a step of molding the second powdered mixture into a
molded body having a predetermined shape; and a step of baking the
molded body for sintering at 1,200 to 1,600.degree. C. for 0.5 to
20 hours.
12. A solid oxide fuel cell provided with an electrolyte comprising
an oxide ion conductor according to one of claims 1 and 6.
13. A gas sensor comprising an oxide ion conductor according to one
of claims 1 and 6.
14. An oxygen separation membrane for use in an electrochemical
oxygen pump, comprising an oxide ion conductor according to one of
claims 1 and 6.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to oxide ion conductors which
are effectively used for electrolytes or air electrodes for fuel
cells, gas sensors such as oxygen gas sensors, oxygen separation
membranes for electrochemical oxygen pumps and the like, gas
separation membranes, and the like.
[0003] 2. Description of the Related Art
[0004] As a typical example of conventional oxide ion conductors, a
solid solution having a cubic fluorite system is known as "a
stabilized zirconia" in which a small amount of a divalent or a
trivalent metal oxide, such as CaO, MgO, Y.sub.2O.sub.3, or
Gd.sub.2O.sub.3, is dissolved in zirconium oxide (ZrO.sub.2). A
stabilized zirconia has superior heat stability, and in addition,
has an advantage in which the ionic transference number (a ratio of
oxide ionic conduction to electrical conduction) does not tend to
decrease even if the oxygen partial pressure is decreased since the
oxide ion conduction is dominant at all oxygen partial pressures
from an oxygen atmosphere to a hydrogen atmosphere. Accordingly, a
stabilized zirconia is widely used as zirconia (oxygen) sensors for
various industrial process controls, such as for steel
manufacturing, and for combustion control (an air-fuel ratio) for
automobiles. In addition, a stabilized zirconia is also used as an
electrolyte for a solid oxide fuel cell (SOFC) under development,
which is operated at approximately 1,000.degree. C.
[0005] However, the oxide ionic conduction of a stabilized zirconia
is not sufficiently high, and in particular, the conduction thereof
becomes deficient when a temperature is decreased. For example, the
ionic conductivity of Y.sub.2O.sub.3-stabilized zirconia is
10.sup.-1 S/cm at 1,000.degree. C. but is decreased to 10.sup.-4
S/cm at 500.degree. C., whereby there is an inconvenient limitation
in which the operating temperature must be controlled at a higher
temperature, such as 800.degree. C. or more.
[0006] In order to solve the problems described above, an oxide ion
conductor having a perovskite structure is proposed provided with
oxide ionic conduction higher than that of a stabilized zirconia
(refer to Japanese Unexamined Patent Application Publication Nos.
11-228136, 11-335164). These oxide ion conductors mentioned above
are compound oxides composed of four elements or five elements, and
an oxide ion conductor disclosed in Japanese Unexamined Patent
Application Publication No. 11-335164 is a substance represented by
the formula Ln.sub.1-xA.sub.xGa.sub.1-y-zB1.sub.yB2.sub.zO.sub.3 in
which Ln is a lanthanoid rare earth metal, A is an alkaline earth
metal, B1 is a non-transition metal, and B2 is a transition metal.
That is, this oxide ion conductor has a basic lanthanoid.gallate
(LnGaO.sub.3) structure and is a compound oxide composed of five
elements (Ln+A+Ga+B1+B2) formed by doping three elements, i.e., an
alkaline earth metal (A), a non-transition metal (B1), and a
transition metal (B2), in the lanthanoid.gallate structure, or is a
compound oxide composed of four elements (Ln+A+Ga+B2) formed by
doping two elements, i.e., an alkaline earth metal (A), and a
transition metal (B2), in the lanthanoid.gallate structure.
[0007] The oxide ion conductor described above has oxide ionic
conduction higher than that of a stabilized zirconia and has
superior heat stability, in which the high oxide ionic conduction
thereof can be maintained at a higher temperature and also even at
a lower temperature. Furthermore, it is confirmed that the decrease
in ionic transference number is preferably small at all oxygen
partial pressures from an oxygen atmosphere to a hydrogen
atmosphere (i.e., even at a lower oxygen partial pressure), and
that oxide ionic conduction is dominant, or mixed ionic conduction
is observed.
[0008] However, in the oxide ion conductor disclosed in Japanese
Unexamined Patent Application Publication No. 11-228136, there is a
problem in that the oxide ionic conduction is low, and in the oxide
ion conductor disclosed in Japanese Unexamined Patent Application
Publication No. 11-335164, there is a problem, which must be
overcome, in that the mechanical strength is not sufficient. Since
an oxide ion conductor is used in a manner in which gases having
different compositions from each other are supplied at the front
and the rear surfaces of the oxide ion conductor, respectively, to
contact thereon so that reactions occur, when cracks or continuous
pores are formed in the oxide ion conductor, the gases at the front
and the rear surfaces thereof leak through the cracks or the
continuous pores. When the gases leak, the performance of the
component is decreased, the efficiency thereof is significantly
degraded, and in addition, the entire component may be seriously
damaged.
SUMMARY OF THE INVENTION
[0009] Accordingly, it is an object of the present invention to
provide an oxide ion conductor having a relatively high mechanical
strength while the ionic conduction is maintained at a level
sufficient in practical use.
[0010] An oxide ion conductor of the present invention is
represented by the formula Ln1AGaB1B2B3O.
[0011] In the oxide ion conductor of the present invention, Ln1 is
at least one element selected from the group consisting of La, Ce,
Pr, Nd, and Sm, in which the content thereof is 43.6 to 51.2
percent by weight; A is at least one element selected from the
group consisting of Sr, Ca, and Ba, in which the content thereof is
5.4 to 11.1 percent by weight; the content of Ga is 20.0 to 23.9
percent by weight; B1 is at least one element selected from the
group consisting of Mg, Al, and In; B2 is at least one element
selected from the group consisting of Co, Fe, Ni, and Cu; and B3 is
at least one element selected from the group consisting of Al, Mg,
Co, Ni, Fe, Cu, Zn, Mn, and Zr, wherein, in the case in which B3 is
an element differing from B1 or B2, the content of B1 is 1.21 to
1.76 percent by weight, the content of B2 is 0.84 to 1.26 percent
by weight, and the content of B3 is 0.23 to 3.08 percent by weight,
and in the case in which B3 is an element equal to B1 or B2, the
total content of B1 and B3 is 1.41 to 2.70 percent by weight, and
the total content of B2 and B3 is 1.07 to 2.10 percent by
weight.
[0012] An oxide ion conductor of the present invention is
represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sup.wO.sub-
.3-d.
[0013] In the oxide ion conductor of the present invention
described above, Ln1 is at least one element selected from the
group consisting of La, Ce, Pr, Nd, and Sm; A is at least one
element selected from the group consisting of Sr, Ca and Ba; B1 is
at least one element selected from the group consisting of Mg, Al,
and In; B2 is at least one element selected from the group
consisting of Co, Fe, Ni, and Cu; and B3 is at least one element
selected from the group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn,
Mn, and Zr, wherein x is 0.05 to 0.3, y is 0.025 to 0.29, z is 0.01
to 0.15, w is 0.01 to 0.15, y+z+w is 0.035 to 0.3, and d is 0.04 to
0.3.
[0014] According to the oxide ion conductors of the present
invention described above, represented by the formulas
Ln1AGaB1B2B3O and
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d,
the oxide ionic conduction thereof is higher than that of an oxide
ion conductor composed of a conventional stabilized zirconia, and
the mechanical strength is higher than that of an oxide ion
conductor disclosed in Japanese Unexamined Patent Application
Publication No. 11-335164, composed of a five-element
(Ln+A+Ga+B1+B2) compound oxide or a four-element (Ln+A+Ga+B2)
compound oxide.
[0015] In the oxide ion conductor represented by the formula
Ln1AGaB1B2B30 described above, first crystal grains composed of
elements Ln1, A, and Ga and second crystal grains composed of
element B1 may be present between matrix crystal grains other than
the first crystal grains and the second crystal grains.
[0016] In the oxide ion conductor represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d,
described above, wherein first crystal grains composed of elements
Ln1, A, and Ga and second crystal grains composed of element B1 may
be present between matrix crystal grains other than the first
crystal grains and the second crystal grains.
[0017] In the oxide ion conductor represented by the formula
Ln1AGaB1B2B30, described above, the first crystal grains composed
of elements Ln1, A, and Ga and the second crystal grains composed
of an element B1 may be present in the matrix crystal grains other
than the first crystal grains and the second crystal grains.
[0018] In the oxide ion conductor represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d
described above, the first crystal grains composed of elements Ln1,
A, and Ga and the second crystal grains composed of element B1 may
be present in the matrix crystal grains other than the first
crystal grains and the second crystal grains.
[0019] In the present invention, as described above, since the
first crystal grains and the second crystal grains may be present
between the matrix crystal grains or in the matrix crystal grains,
the growth of the matrix crystal grains can be suppressed, and
hence, the mechanical strength of the oxide ion conductor can be
improved while the ionic conduction thereof is maintained at a
level to be required.
[0020] In the oxide ion conductor represented by the formula
Ln1AGaB1B2B30 according to the present invention, the grain
diameters of the first crystal grains and the second crystal grains
are preferably 0.1 to 2.0 .mu.m.
[0021] In the oxide ion conductor represented by the formula
Ln1AGaB1B2B3O according to the present invention, the grain
diameter of the matrix crystal grains is preferably 2.0 to 7.0
.mu.m.
[0022] In the oxide ion conductor represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d
according to the present invention, the grain diameters of the
first and the second crystal grains are preferably 0.1 to 2.0
.mu.m.
[0023] In the oxide ion conductor represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d
according to the present invention, the grain diameter of the
matrix crystal grains is preferably 2.0 to 7.0 .mu.m.
[0024] In the oxide ion conductors represented by the formula
Ln1AGaB1B2B3O and represented by the formula
Ln1.sub.1-xA.sub.xGa.sub.1-y- -z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d
according to the present invention, the growth of the matrix
crystal grains can be effectively suppressed so as to sufficiently
improve the mechanical strength of the oxide ion conductor.
[0025] A method for manufacturing an oxide ion conductor
represented by the formula Ln1AGaB1B2B3O according to the present
invention, comprises a step of mixing individual powdered oxides
composed of Ln1, A, Ga, B1, and B2 in accordance with the ratios
described above so as to form a first powdered mixture, a step of
calcining the first powdered mixture at 500 to 1,300.degree. C. for
1 to 10 hours so as to form calcined powder; a step of mixing the
powdered oxide composed of B3 with calcined powder in accordance
with the ratio described above so as to form a second powdered
mixture; a step of molding the second powdered mixture so as to
form a molded body having a predetermined shape; and a step of
baking the molded body for sintering at 1,200 to 1,600.degree. C.
for 0.5 to 20 hours.
[0026] A solid oxide fuel cell according to the present invention
is provided with an electrolyte comprising one of the oxide ion
conductors represented by the formulas Ln1AGaB1B2B3O and
Ln1.sub.1-xA.sub.xGa.sub.1--
y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d.
[0027] A gas sensor according to the present invention comprises
one of the oxide ion conductors represented by the formulas
Ln1AGaB1B2B3O and
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d.
[0028] An oxygen separation membrane for use in an electrochemical
oxygen pump according to the present invention comprises one of the
oxide ion conductors represented by the formulas Ln1AGaB1B2B3O and
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d.
[0029] In the present invention, the "oxide ion conductor" means a
narrowly defined oxide ion conductor in which the electrical
conduction is dominantly performed by the oxide ionic conduction.
That is, a material is not included in the oxide ion conductor,
which is called an electron-ion mixed conductor or an oxide ion
mixed conductor, in which the electronic conduction and the ionic
conduction serve important roles in electrical conduction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a SEM photograph of an oxide ion conductor of
Example 4, which is composed of LSGMC mixed with 2 percent by
weight of Al.sub.2O.sub.3;
[0031] FIG. 2 is a SEM photograph of an oxide ion conductor of
Example 12, which is composed of LSGMC mixed with 3.6 percent by
weight of MgO;
[0032] FIG. 3 is a SEM photograph of an oxide ion conductor of
Example 19, which is composed of LSGMC mixed with 2 percent by
weight of ZrO.sub.2;
[0033] FIG. 4 is a SEM photograph of an oxide ion conductor of
Comparative Example 1, which is composed of LSGMC mixed with no
additive; and
[0034] FIG. 5 is a schematic view showing a structure of a solid
oxide fuel cell using an oxide ion conductor of the present
invention as a solid electrolyte.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Next, the embodiments of the present invention will be
described.
[0036] An oxide ion conductor of the present invention is
represented by the formula (1) shown below.
Ln1.sub.1-xA.sub.xGa.sub.1-y-z-wB1.sub.yB2.sub.zB3.sub.wO.sub.3-d
(1)
[0037] In the formula (1) shown above, Ln1 is a lanthanoid rare
earth metal element and is at least one selected from the group
consisting of La, Ce, Pr, Nd, and Sm. A is an alkaline earth metal
and is at least one element selected from the group consisting of
Sr, Ca, and Ba. B1 is a non-transition metal and is at least one
element selected from the group consisting of Mg, Al, and In. B2 is
a transition metal and is at least one element selected from the
group consisting of Co, Fe, Ni, and Cu. B3 is a metal added for
improving the mechanical strength and is at least one element
selected from the group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn,
Mn, and Zr. That is, the oxide ion conductor of the present
invention has a basic lanthanoid.gallate (LnGaO.sub.3-d) structure
and is a compound oxide composed of six elements (Ln+A+Ga+B1+B2+B3)
formed by doping four elements, i.e., the alkaline earth metal (A),
the non-transition metal (B1), the transition metal (B2), and the
metal (B3) for improving the mechanical strength, in the oxide ion
conductor.
[0038] In addition, the oxide ion conductor represented by the
formula (1) has a perovskite crystal structure, in which A sites of
the perovskite structure represented by ABO.sub.3-d are occupied by
the elements Ln and A of the formula (1), and B sites are occupied
by the elements Ga, B1, and B3. Since some of the A sites and the B
sites, which are naturally occupied by trivalent metals, are
occupied by divalent metals (for example, the element A occupying
the A sites and the element B occupying the B sites) and the
transition metal (the element B2 occupying the B sites), oxygen
holes are produced, whereby oxide ionic conduction is generated by
the presence of the oxygen holes. Accordingly, oxygen atoms are
decreased corresponding to the number of oxygen holes produced. On
the other hand, since excessive elements are kicked out from a
matrix crystal grain by adding metal B3, the crystal grain becomes
smaller, and hence, the mechanical strength of the oxide ion
conductor is improved.
[0039] The x in the formula (1) is an atomic ratio of the element A
and is set to be 0.05 to 0.3, and preferably, 0.10 to 0.25. The y
is an atomic ratio of the element B1 and is set to be 0.025 to
0.29, and preferably, 0.05 to 0.2. The z is an atomic ratio of the
element B2 and is set to be 0.01 to 0.15, and preferably, 0.03 to
0.1. The w is an atomic ratio of the element B3 and is set to be
0.01 to 0.15, and preferably, 0.03 to 0.1. The (y+z+w) is set to be
0.035 to 0.3, and preferably, 0.10 to 0.25. The reason the x is set
to be 0.05 to 0.3 is that when the x is out of the range mentioned
above, the electrical conduction is decreased. The reason the z is
set to be 0.01 to 0.15 is that the transference number (ratio of
oxide ionic conduction) is decreased concomitant with the increase
in z even though the electrical conduction is increased, and hence,
the range mentioned above is an optimum range. The reason the w is
set to be 0.01 to 0.15 is that the transference number (ratio of
oxide ionic conduction) is decreased concomitant with the increase
in w even though the mechanical strength is increased, and hence,
the range mentioned above is an optimum range. The reason the
(y+z+w) is set to be 0.035 to 0.3 is that the transference number
is decreased concomitant with the increase in (y+z+w) even though
the electrical conduction is increased, and hence, the range
mentioned above is an optimum range.
[0040] The d is set to be 0.04 to 0.3. The reason the atomic ratio
of oxygen is represented by (3-d) in the formula (1) (the actual
atomic ratio of oxygen is 3 or less) is that since the number of
oxygen holes changes according to temperature, oxygen partial
pressure, type of B2 element, and the amount thereof, in addition
to types of elements added (A, B1, B2, and B3), the atomic ratio of
oxygen is difficult to represent accurately. In this connection,
when Co, Fe, Ni, or Cu is used as the element B2, high electrical
conduction is observed at a lower temperature side (approximately
650.degree. C.).
[0041] When the oxide ion conductor described above is represented
by atoms, the oxide ion conductor can be represented by the formula
Ln1AGaB1B2B3O. In the formula above, Ln1 is at least one element
selected from the group consisting of La, Ce, Pr, Nd, and Sm, and
the content thereof is 43.6 to 51.2 percent by weight; A is at
least one element selected from the group consisting of Sr, Ca, and
Ba, and the content thereof is 5.4 to 11.1 percent by weight; and
the content of Ga is 20.0 to 23.9 percent by weight. In addition,
B1 is at least one element selected from the group consisting of
Mg, Al, and In, B2 is at least one element selected from the group
consisting of Co, Fe, Ni, and Cu, and B3 is at least one element
selected from the group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn,
Mn, and Zr. In the case in which B3 is an element differing from B1
or B2, the content of B1 is 1.21 to 1.76 percent by weight, the
content of B2 is 0.84 to 1.26 percent by weight, and the content of
B3 is 0.23 to 3.08 percent by weight. On the other hand, in the
case in which B3 is an element equal to B1 or B2, the total content
of B1 and B3 is 1.41 to 2.70 percent by weight, and the total
content of B2 and B3 is 1.07 to 2.10 percent by weight.
[0042] The oxide ion conductor of the present invention can be
manufactured by a process comprising steps of mixing well
individual oxides having component elements at a predetermined
mixing ratio, molding the mixture thus formed by an appropriate
method, and baking the molded mixture for sintering. As powdered
starting materials, in addition to the oxides, precursors (for
example, carbonates, and carboxylic acids and the derivatives
thereof) can be used which are converted into oxides by pyrolysis.
As a preferable method for molding the mixture, a doctor blade
method may be mentioned. The baking temperature for sintering is
1,200.degree. C. or more, and preferably, 1,300.degree. C. or more,
and the baking time ranges from several hours to several tens of
hours. In order to shorten the baking time, pre-baking may be
performed at a temperature lower than the sintering temperature of
the mixture of the starting materials. For example, the pre-baking
may be performed at 500 to 1,300.degree. C. for 1 to 10 hours. The
pre-baked mixture is molded after a step of pulverizing when
necessary and is finally sintered. Various molding methods may be
optionally used, such as uniaxial compression molding, isostatic
pressing, extrusion molding, and tape casting. Baking including
pre-baking is preferably performed in an oxidative atmosphere, such
as in the air, or in an inert gas atmosphere.
[0043] That is, a preferable method for manufacturing the oxide ion
conductor comprises steps of mixing individual powdered oxides
including component elements Ln1, A, Ga, B1, and B2 at a
predetermined mixing ratio so as to form a first powdered mixture,
calcining the first powdered mixture at 500 to 1,300.degree. C. for
1 to 10 hours so as to form calcined powder, mixing a powdered
oxide including the element B3 with the calcined powder at a
predetermined mixing ratio so as to form a second powdered mixture,
molding the second powdered mixture into a molded body having a
predetermined shape, and baking the molded body for sintering at
1,200 to 1,600.degree. C. for 0.5 to 20 hours.
[0044] In the oxide ion conductor thus sintered, first crystal
grains composed of Ln1, A, and Ga, and second crystal grains
composed of B1 are present between matrix crystal grains other than
the first and the second crystal grains. That is, the first crystal
grains are composed of at least one element selected from the group
consisting of La, Ce, Pr, Nd, and Sm, at least one element selected
from the group consisting of Sr, Ca, and Ba, and Ga; and the second
crystal grains are composed of at least one selected from the group
consisting of Mg, Al, and In. The matrix crystal grains are crystal
grains other than the first and the second crystal grains. Since
the first and the second crystal grains are present between the
matrix crystal grains or are present therein, the growth of the
matrix crystal grains is suppressed, and hence, the diameter of the
matrix crystal grains are smaller compared to that of conventional
crystal grains which do not have the first and the second crystal
grains, whereby the mechanical strength can be improved. The grain
diameters of the first and the second crystal grains are preferably
0.1 to 2.0 .mu.m, and the volume fractions of the first and the
second crystal grains are preferably 0.5 to 20 percent by volume.
The grain diameter of the first crystal grains is more preferably
0.5 to 2.0 .mu.m, and the volume fraction thereof is more
preferably 1 to 10 percent by volume. The grain diameter of the
matrix crystal grains, the growth of which is suppressed, is
preferably 2.0 to 7.0 .mu.m.
[0045] In the oxide ion conductor of the present invention, the
oxide ionic conduction is dominant in the electrical conduction
(that is, the ionic transference number is 0.7 or more), and the
oxide ion conductor of the present invention is a narrowly defined
oxide ion conductor. This material can be used for applications
(for example, electrolytes for solid oxide fuel cells, and gas
sensors) of various oxide ion conductors, in which a stabilized
zirconia is conventionally used. Since this type of oxide ion
conductor of the present invention has higher oxide ionic
conduction than that of a stabilized zirconia and is functional at
a lower temperature, it is believed that products having superior
performance can be manufactured by using this material than those
manufactured by using a conventional stabilized zirconia.
[0046] That is, since the oxide ion conductor of the present
invention has oxide ionic conduction significantly superior to that
of a conventional stabilized zirconia, for example, in the case in
which a solid oxide fuel cell is formed by using an electrolyte
composed of a thick film 0.5 mm (equal to 500 .mu.m) thick which
can be formed by a sintering method, a higher output can be
obtained by using the oxide ion conductor of the present invention
than that obtained by using the stabilized zirconia described
above. In FIG. 5, a typical solid oxide fuel cell 1 is shown. The
oxide ion conductor of the present invention is used as a solid
electrolyte layer 3, and the solid electrolyte layer 3 is provided
between an air electrode layer 2 and a fuel electrode layer 4 so as
to form a planar type single cell. This single cell is held between
a separator 7 at the air electrode side and a separator 8 at the
fuel electrode side, each separator is coated with current
collectors 6 and 6, respectively, by using washers 9 and 9. In this
solid oxide fuel cell 1, power generation is performed by supplying
oxygen (air) to the air electrode layer 2 via a supply opening 7a
provided in the separator 7 at the air electrode side and by
supplying a fuel gas (H.sub.2, CO, or the like) to the fuel
electrode layer 4 via a supply opening 8a provided in the separator
8 at the fuel electrode side. The oxygen supplied to the air
electrode layer 2 reaches the vicinity of the interface with the
solid electrolyte layer 3 via pores in the air electrode layer 2
and receives electrons from the air electrode layer 2 at this
interface, whereby the oxygen is ionized to form oxide ions
(O.sup.2-). The oxide ions permeate the solid electrolyte layer 3
toward the fuel electrode layer 4. The oxide ions, which reach the
vicinity of the interface with the fuel electrode layer 4, react
with the fuel gas at the interface and generate a reaction product
(H.sub.2O, CO.sub.2, or the like), whereby electrons are discharged
to the fuel electrode. By collecting the electrons using the
current collectors 6 and 6, current can be obtained.
[0047] Accordingly, the solid electrolyte layer 3 is a permeation
media for the oxide ions, and even though depending on type of
element B2 and the atomic ratio thereof, the maximum output density
of the solid oxide fuel cell 1 using the oxide ion conductor of the
present invention as the oxide electrolyte layer 3 exceeds that of
a solid oxide fuel cell using a thin film 30 .mu.m thick composed
of a stabilized zirconia at an operating temperature of
1,000.degree. C. and is several times (for example, 3 times or
more) larger than that at an operating temperature of 800.degree.
C. In addition, when a film approximately 200 .mu.m thick is used,
an output density can be obtained at a lower temperature, such as
600 or 700.degree. C., which is equivalent to that obtained at
1,000.degree. C. by using a stabilized zirconia film 30 .mu.m
thick.
[0048] When the oxide ion conductor of the present invention is
used as an electrolyte for a solid oxide fuel cell, materials to be
used may be selected in accordance with an operating temperature.
For example, in the case in which turbine generation using exhaust
gases is performed as cogeneration, since a high operating
temperature is required, such as approximately 1,000.degree. C., it
is preferable that an electrolyte be composed of the oxide ion
conductor containing Co or Fe as the element B2, which exhibits
high oxide ionic conduction at a higher temperature, and more
preferably, the oxide ion conductor containing Co is used. On the
other hand, when an operating temperature is approximately
800.degree. C., in addition to the oxide ion conductor mentioned
above, the oxide ion conductor containing Ni as the element B2 may
be used, and when an operating temperature is 600.degree. C. or
less, the oxide ion conductor containing Cu as the element B2 may
be used.
[0049] In the case in which an operating temperature is low, such
as 600 to 700.degree. C., when generation is simultaneously
performed by using steam or other exhaust gases, or the energy
thereof is effectively used as a heat source, the generation
efficiency of the solid oxide fuel cell is not seriously decreased.
When an operating temperature is lower as described above, since a
steel material such as a stainless steel can be used as a
structural material for the solid oxide fuel cell, there is an
advantage in that the material cost can be significantly decreased
compared to a material, such as a Ni--Cr alloy, or a ceramic, which
must be used when an operating temperature is approximately
1,000.degree. C. A solid oxide fuel cell functional at a lower
temperature as described above cannot be constructed by using a
conventional stabilized zirconia; however, according to the present
invention, a solid oxide fuel cell can be constructed which is
functional at from a lower to a higher operating temperature in
accordance with the condition to be used.
[0050] Since the oxide ion conductor of the present invention
exhibits high oxide ionic conduction in a wide range of
temperature, the oxide ion conductor can be satisfactory used as an
electrolyte for a solid oxide fuel cell which is operated at a
relatively lower temperature, such as 600 to 700.degree. C. and at
a high temperature, such as approximately 1,000.degree. C. As a
result, when the oxide ion conductor is selected as an electrolyte,
various solid oxide fuel cells from a low temperature-operating
type to a high temperature-operating type can be constructed only
by using this oxide ion conductor.
[0051] The largest application of a stabilized zirconia is
currently in oxygen sensors, and a large number of the sensors are
used for air-fuel control for automobiles and are also used for
controlling industrial processes for steel manufacturing and the
like. The oxygen sensor described above is called a solid
electrolyte oxygen sensor and is used for measuring an oxygen
concentration based on the principle of an oxygen concentration
cell. That is, when an oxygen partial pressure at one end of a
material composed of an oxide ion conductor differs from that at
the other end of the material, oxide ions permeate the material to
form a oxygen concentration cell; hence, the oxygen partial
pressure can be detected by measuring the electromotive force by
providing electrodes at the both ends. The solid electrolyte oxygen
sensor can also be used for gases containing oxygen, such as
SO.sub.x and NO.sub.x, in addition to an oxygen gas.
[0052] The oxygen sensors formed of a stabilized zirconia are
relatively inexpensive; however, since the oxide ionic conduction
is decreased at a lower temperature and can only be used at a
higher temperature of 600.degree. C. or more, the applications
thereof are restricted. In contrast, since the oxide ion conductor
of the present invention, in which the oxide ionic conduction is
dominant, exhibits higher oxide ionic conduction compared to that
of a stabilized zirconia, they can be effectively used for gas
sensors, and particularly, for oxygen sensors, and in addition,
since the oxide ionic conduction is high even at a lower
temperature, a gas sensor formed of the oxide ion conductor of the
present invention can be satisfactory used at 600.degree. C. or
less.
[0053] In addition, the oxide ion conductor of the present
invention, in which the oxide ionic conduction is dominant, can
also be used as an oxygen separation membrane for an
electrochemical oxygen pump. When a potential difference is applied
between two ends of a separation membrane composed of an oxide ion
conductor, the oxide ions permeate the membrane, and current flows,
whereby oxygen flows in one direction from one end to the other end
of the membrane. This is the oxygen pump. For example, when air is
supplied from one end of the membrane, oxygen-enriched air can be
obtained at the other end of the membrane, whereby the oxide ion
conductor is used as an oxygen separation membrane. The oxygen
separation membranes described above are used in, for example,
military aircraft or helicopters for producing oxygen-enriched air
form the thin air of the surrounding area. It is also believed that
the oxide separation membrane may be used instead of oxygen
cylinders for medical use.
[0054] The gas separation membrane described above can also be used
for, for example, decomposition of water and NO.sub.x, in addition
to oxygen separation. In the case in which water is decomposed on
the surface of a separation membrane into oxide ions and hydrogen,
since a difference of oxide ion concentration is generated between
the two ends of the membrane, the flow of the oxide ions is
produced by a driving force of the difference described above, and
the hydrogen does not flow but remains, whereby hydrogen can be
produced from water. In the case in which NO.sub.x is decomposed,
the NO.sub.x is turned into harmless substances and is decomposed
into nitrogen and oxygen.
[0055] In addition, the oxide ion conductor of the present
invention may be used for electrochemical reactors or separation
membranes for isotopic oxygen.
EXAMPLES
[0056] Next, the examples of the present invention will be
described in detail together with the comparative examples.
Examples 1 to 7
[0057] A basic powdered mixture (hereinafter referred to as
"LSGMC") was prepared which was composed of powdered metal oxides,
La.sub.2O.sub.3, La.sub.2 SrCO.sub.3, Ga.sub.2O.sub.3, MgO, and
CoO, in accordance with ratios so as to form
La.sub.0.8Sr.sub.0.2Ga.sub.0.8Mg.sub.0.15Co.sub.0.05- O.sub.3.
[0058] After a powdered material composed of Al.sub.2O.sub.3 was
mixed with the powdered mixture in a ratio in accordance with that
shown in Table 1, toluene and n-butanol were added thereto as a
solvent so as to impart fluidity to the mixture, and a film having
a thickness of 0.25 to 0.30 mm was then formed by a doctor blade
method. Subsequently, the film thus formed was sintered at
1,450.degree. C. for 6 hours, thereby yielding an oxide ion
conductor. Oxide ion conductors formed in a manner described above
were used for Examples 1 to 7.
Examples 8 to 15
[0059] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of MgO was mixed with the powdered mixture described above
in a ratio in accordance with that shown in Table 1, the same
solvent as that used in Example 1 was added, a film was then formed
having the same thickness as that in Example 1 by a doctor blade
method, and an oxide ion conductor was obtained by sintering under
the same condition as that in Example 1. Oxide ion conductors
formed in a manner described above were used for Example 8 to
15.
Examples 16 to 22
[0060] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of ZrO.sub.2 was mixed with the powdered mixture described
above in a ratio in accordance with that shown in Table 1, the same
solvent as that used in Example 1 was added, a film was then formed
having the same thickness as that in Example 1 by a doctor blade
method, and an oxide ion conductor was obtained by sintering under
the same condition as that in Example 1. Oxide ion conductors
formed in a manner described above were used for Example 16 to
22.
Examples 23 to 26
[0061] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of Al.sub.2O.sub.3 and MgO is mixed with the powdered
mixture described above in a ratio in accordance with that shown in
Table 2, the same solvent as that used in Example 1 is added, a
film is then formed having the same thickness as that in Example 1
by a doctor blade method, and an oxide ion conductor is obtained by
sintering under the same condition as that in Example 1. Oxide ion
conductors formed in a manner described above are used for Example
23 to 26.
Examples 27 to 30
[0062] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of Al.sub.2O.sub.3 and ZrO.sub.2 is mixed with the
powdered mixture described above in a ratio in accordance with that
shown in Table 2, the same solvent as that used in Example 1 is
added, a film is then formed having the same thickness as that in
Example 1 by a doctor blade method, and an oxide ion conductor is
obtained by sintering under the same condition as that in Example
1. Oxide ion conductors formed in a manner described above are used
for Example 27 to 30.
Examples 31 to 34
[0063] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of MgO and ZrO.sub.2 is mixed with the powdered mixture
described above in a ratio in accordance with that shown in Table
2, the same solvent as that used in Example 1 is added, a film is
then formed having the same thickness as that in Example 1 by a
doctor blade method, and an oxide ion conductor is obtained by
sintering under the same condition as that in Example 1. Oxide ion
conductors formed in a manner described above are used for Example
31 to 34.
Examples 35 to 39
[0064] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of Al.sub.2O.sub.3, MgO, and ZrO.sub.2 is mixed with the
powdered mixture described above in a ratio in accordance with that
shown in Table 2, the same solvent as that used in Example 1 is
added, a film is then formed having the same thickness as that in
Example 1 by a doctor blade method, and an oxide ion conductor is
obtained by sintering under the same condition as that in Example
1. Oxide ion conductors formed in a manner described above are used
for Example 35 to 39.
Examples 40 to 46
[0065] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of CoO is mixed with the powdered mixture described above
in a ratio in accordance with that shown in Table 3, the same
solvent as that used in Example 1 is added, a film is then formed
having the same thickness as that in Example 1 by a doctor blade
method, and an oxide ion conductor is obtained by sintering under
the same condition as that in Example 1. Oxide ion conductors
formed in a manner described above are used for Example 40 to
46.
Examples 47 to 53
[0066] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of Fe.sub.2O.sub.3 is mixed with the powdered mixture
described above in a ratio in accordance with that shown in Table
3, the same solvent as that used in Example 1 is added, a film is
then formed having the same thickness as that in Example 1 by a
doctor blade method, and an oxide ion conductor is obtained by
sintering under the same condition as that in Example 1. Oxide ion
conductors formed in a manner described above are used for Example
47 to 53.
Examples 54 to 60
[0067] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of NiO is mixed with the powdered mixture described above
in a ratio in accordance with that shown in Table 3, the same
solvent as that used in Example 1 is added, a film is then formed
having the same thickness as that in Example 1 by a doctor blade
method, and an oxide ion conductor is obtained by sintering under
the same condition as that in Example 1. Oxide ion conductors
formed in a manner described above are used for Example 54 to
60.
Examples 61 to 67
[0068] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of CuO is mixed with the powdered mixture in a ratio in
accordance with that shown in Table 4, the same solvent as that
used in Example 1 is added, a film is then formed having the same
thickness as that in Example 1 by a doctor blade method, and an
oxide ion conductor is obtained by sintering under the same
condition as that in Example 1. Oxide ion conductors formed in a
manner as described above are used for Example 61 to 67.
Examples 68 to 74
[0069] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of ZnO is mixed with the powdered mixture described above
in a ratio in accordance with that shown in Table 4, the same
solvent as that used in Example 1 is added, a film is then formed
having the same thickness as that in Example 1 by a doctor blade
method, and an oxide ion conductor is obtained by sintering under
the same condition as that in Example 1. Oxide ion conductors
formed in a manner described above are used for Example 68 to
74.
Examples 75 to 80
[0070] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. After a powdered material
composed of MnO is mixed with the powdered mixture in a ratio in
accordance with that shown in Table 4, the same solvent as that
used in Example 1 is added, a film is then formed having the same
thickness as that in Example 1 by a doctor blade method, and an
oxide ion conductor is obtained by sintering under the same
condition as that in Example 1. Oxide ion conductors formed in a
manner described above are used for Example 75 to 80.
Comparative Examples 1
[0071] The same solvent as that used in Example 1 was added to the
powdered mixture prepared in Example 1 having no additive therein,
a film was then formed having the same thickness as that in Example
1 by a doctor blade method, and the film thus formed was sintered
under the same condition as that in Example 1, whereby an oxide ion
conductor was obtained which was used as the standard for
comparison. This oxide ion conductor (non-doped LSGMC) was used for
Comparative Example 1.
Comparative Examples 2 to 14
[0072] A powdered mixture was prepared which was composed of the
same LSGMC as that prepared in Example 1. Powdered metal oxides
composed of Al.sub.2O.sub.3, MgO, ZrO.sub.2, CoO, Fe.sub.2O.sub.3,
NiO, CuO, and MnO were selected as shown in Tables 1 and 4, and
each selected powdered metal oxide was mixed with the powdered
mixture described above in a ratio in accordance with that shown in
Tables 1 to 4. Subsequently, the same solvent as that used in
Example 1 was added, a film was then formed having the same
thickness as that in Example 1 by a doctor blade method, and an
oxide ion conductor was obtained by sintering under the same
condition as that in Example 1. The oxide ion conductors formed in
a manner described above were used for Comparative Example 2 to
14.
[0073] Comparative Evaluation
[0074] The oxide ion conductors thus formed were observed by a
scanning electron microscope (SEM) and were analyzed by an electron
probe micro analyzer (EPMA), and in addition, the resistivities of
the oxide ion conductors at 650 and 800.degree. C. and the
mechanical strengths thereof were measured. The measurement of the
resistivity was conducted by steps of coating platinum paste to be
used as electrodes on each sample thus prepared, connecting
platinum wires and baking at 950 to 1,200.degree. C. for 10 to 60
minutes, and measuring the resistivities by a DC four-point probe
method or by an AC two-point probe method in a chamber in which a
oxygen partial pressure and a temperature were optionally
controlled. An oxygen partial pressure was controlled by using
mixed gases, i.e., O.sub.2--N.sub.2, CO--CO.sub.2, and
H.sub.2--H.sub.2O.
[0075] Concerning the measurement of the mechanical strength, a
test piece 4 mm by 4 mm by 0.23 mm was cut away from the sample
thus formed, and a three-point bending test was performed by using
the test piece. The results are shown in Tables 1 to 4.
[0076] The results of EPMA analysis, resistivities, and mechanical
strengths obtained for Examples 1 to 80 and for Comparative
Examples 1 to 14 are shown in Tables 1 to 4. In addition, the SEM
photographs of the oxide ion conductors of Examples 4, 12, and 19
are shown in FIGS. 1 to 3, in that order, and the SEM photograph of
the oxide ion conductor of Comparative Example 1 used as the
standard is shown in FIG. 4.
1 TABLE 1 Resistivity Resistivity Strength Manufacturing Content of
element (wt %) (.OMEGA. cm) at (.OMEGA. cm) at (kgf/mm.sup.2)
method La Sr Ga Mg Co Al/Zr 650.degree. C. 800.degree. C. at R.T.
Comparative Non-dope LSGMC 47.12 7.43 23.65 1.55 1.25 0.00 19.23
5.99 19.98 Example 1 Example 1 Al.sub.2O.sub.3-0.05 wt % LSGMC
47.52 7.26 23.26 1.52 1.20 0.23 19.52 6.32 21.54 Example 2
Al.sub.2O.sub.3-0.2 wt % LSGMC 47.60 7.23 23.21 1.51 1.15 0.29
20.64 7.86 24.79 Example 3 Al.sub.2O.sub.3-1 wt % LSGMC 48.74 6.52
22.51 1.50 1.15 0.57 22.32 8.6 26.03 Example 4 Al.sub.2O.sub.3-2 wt
% LSGMC 49.93 5.67 21.54 1.50 1.16 1.14 41.52 13.52 29.08 Example 5
Al.sub.2O.sub.3-3 wt % LSGMC 50.64 5.55 50.91 1.48 1.11 1.30 58.71
18.53 26.05 Example 6 Al.sub.2O.sub.3-4 wt % LSGMC 50.93 5.49 20.47
1.48 1.09 1.52 76.51 24.32 25.32 Example 7 Al.sub.2O.sub.3-5 wt %
LSGMC 51.14 5.47 20.09 1.49 1.09 1.70 95.48 31.59 24.65 Comparative
Al.sub.2O.sub.3-6 wt % LSGMC 51.48 5.29 19.86 1.47 1.04 1.84 114.95
37.84 23.47 Example 2 Example 8 MgO-0.05 wt % LSGMC 47.32 7.28
23.64 1.57 1.20 0.00 20.37 6.27 20.85 Example 9 MgO-0.2 wt % LSGMC
47.44 7.20 23.63 1.60 1.12 0.00 20.78 6.99 21.76 Example 10 MgO-1
wt % LSGMC 47.11 7.57 23.50 1.70 1.10 0.00 21.51 7.18 23.19 Example
11 MgO-1.8 wt % LSGMC 46.82 8.04 23.05 1.94 1.09 0.00 22.94 7.27
25.74 Example 12 MgO-3.6 wt % LSGMC 46.20 8.75 22.71 2.14 1.10 0.00
25.04 7.96 27.47 Example 13 MgO-5.4 wt % LSGMC 45.45 9.40 22.75
2.19 1.08 0.00 30.6 9.67 24.47 Example 14 MgO-10 wt % LSGMC 45.39
9.60 22.48 2.34 1.03 0.00 62.34 20.96 23.75 Example 15 MgO-15 wt %
LSGMC 45.05 10.14 22.03 2.62 0.96 0.00 94.65 33.12 22.69
Comparative MgO-16 wt % LSGMC 44.98 10.33 21.81 2.77 0.89 0.00
116.97 37.49 20.97 Example 3 Example 16 ZrO.sub.2-0.05 wt % LSGMC
47.24 7.40 23.51 1.56 1.20 0.27 19.97 6.73 23.51 Example 17
ZrO.sub.2-0.2 wt % LSGMC 47.95 6.91 23.24 1.56 1.15 0.66 23.55 7.64
24.86 Example 18 ZrO.sub.2-1 wt % LSGMC 48.29 6.73 23.05 1.57 1.03
1.08 26.43 7.99 31.42 Example 19 ZrO.sub.2-2 wt % LSGMC 48.59 6.64
22.70 1.58 0.98 1.67 32.88 9.79 32.12 Example 20 ZrO.sub.2-3 wt %
LSGMC 48.93 6.50 22.33 1.60 0.96 2.22 50.73 16.42 33.37 Example 21
ZrO.sub.2-4 wt % LSGMC 49.15 6.39 22.20 1.61 0.88 2.49 66.75 23.19
34.29 Example 22 ZrO.sub.2-5 wt % LSGMC 49.42 6.29 21.88 1.59 0.86
3.08 84.67 28.46 35.96 Comparative ZrO.sub.2-6 wt % LSGMC 49.60
6.18 21.83 1.56 0.78 3.39 104.32 35.19 37.42 Example 4
[0077]
2 TABLE 2 Resistivity Resistivity Strength Manufacturing Content of
element (wt %) (.OMEGA. cm) at (.OMEGA. cm) at (kgf/mm.sup.2)
method La Sr Ga Mg Co Al/Zr 650.degree. C. 800.degree. C. at R.T.
Example 23 Al.sub.2O.sub.3 .multidot. MgO-0.05 wt % LSGMC 47.17
7.63 23.14 1.60 1.21 0.23 19.99 6.54 21.89 Example 24
Al.sub.2O.sub.3 .multidot. MgO-0.2 wt % LSGMC 47.16 7.91 22.77 1.64
1.19 0.39 20.78 7.37 22.87 Example 25 Al.sub.2O.sub.3 .multidot.
MgO-1 wt % LSGMC 46.97 8.07 22.59 1.68 1.17 0.46 35.61 7.55 25.34
Example 26 Al.sub.2O.sub.3 .multidot. MgO-3 wt % LSGMC 46.77 8.47
22.14 1.76 1.10 0.67 67.29 11.57 26.41 Comparative Al.sub.2O.sub.3
.multidot. MgO-5 wt % LSGMC 46.58 8.83 21.74 1.89 1.05 0.78 101.02
20.64 24.19 Example 5 Example 27 Al.sub.2O.sub.3 .multidot.
ZrO.sub.2-0.05 wt % LSGMC 47.58 7.36 22.90 1.52 1.21 0.88 19.78
6.49 23.74 Example 28 Al.sub.2O.sub.3 .multidot. ZrO.sub.2-0.2 wt %
LSGMC 48.04 7.02 22.78 1.50 1.18 1.03 21.74 7.53 24.99 Example 29
Al.sub.2O.sub.3 .multidot. ZrO.sub.2-1 wt % LSGMC 48.34 6.88 22.54
1.49 1.13 1.34 24.76 8.23 28.71 Example 30 Al.sub.2O.sub.3
.multidot. ZrO.sub.2-3 wt % LSGMC 48.67 6.65 22.41 1.47 1.08 1.54
54.19 17.09 30.19 Comparative Al.sub.2O.sub.3 .multidot.
ZrO.sub.2-5 wt % LSGMC 51.72 6.51 22.13 1.45 0.98 1.97 102.64 20.94
30.91 Example 6 Example 31 MgO .multidot. ZrO.sub.2-0.05 wt % LSGMC
47.05 7.61 23.44 1.56 1.20 0.43 20.19 6.71 22.09 Example 32 MgO
.multidot. ZrO.sub.2-0.2 wt % LSGMC 46.41 8.26 23.30 1.60 1.14 0.82
20.68 7.43 23.43 Example 33 MgO .multidot. ZrO.sub.2-1 wt % LSGMC
46.18 8.55 23.15 1.64 1.06 1.14 26.89 7.61 25.71 Example 34 MgO
.multidot. ZrO.sub.2-3 wt % LSGMC 45.96 8.86 22.95 4.69 1.02 1.46
49.37 10.69 28.69 Comparative MgO .multidot. ZrO.sub.2-5 wt % LSGMC
42.91 9.04 22.73 1.73 0.97 1.82 100.03 19.64 30.03 Example 7
Example 35 Al.sub.2O.sub.3 .multidot. MgO .multidot. ZrO.sub.2-0.05
wt % 47.18 7.72 22.88 1.58 1.24 0.81 20.31 6.19 20.94 LSGMC Example
36 Al.sub.2O.sub.3 .multidot. MgO .multidot. ZrO.sub.2-0.2 wt %
46.61 8.34 22.65 1.60 1.19 1.17 21.48 7.04 24.69 LSGMC Example 37
Al.sub.2O.sub.3 .multidot. MgO .multidot. ZrO.sub.2-1 wt % LSGMC
46.09 8.88 22.56 1.63 1.10 1.41 22.09 8.31 25.55 Example 38
Al.sub.2O.sub.3 .multidot. MgO .multidot. ZrO.sub.2-3 wt % LSGMC
45.65 9.39 22.31 1.67 1.05 1.73 46.97 13.49 29.17 Example 39
Al.sub.2O.sub.3 .multidot. MgO .multidot. ZrO.sub.2-5 wt % LSGMC
44.69 10.27 22.31 1.71 0.98 1.89 73.49 22.19 30.19 Comparative
Al.sub.2O.sub.3 .multidot. MgO .multidot. ZrO.sub.2-7 wt % LSGMC
43.79 11.23 21.95 1.77 0.97 2.33 119.49 34.76 32.45 Example 8
[0078]
3 TABLE 3 Content of element (wt %) Resistivity Resistivity
Strength Fe/Ni/Cu/Zn/ (.OMEGA. cm) at (.OMEGA. cm) at
(kgf/mm.sup.2) La Sr Ga Mg Co Mn 650.degree. C. 800.degree. C. at
R.T. Example 40 CoO-0.05 wt % LSGMC 45.691 8.609 23.798 1.537 1.334
0.000 19.23 6.43 20.94 Example 41 CoO-0.2 wt % LSGMC 45.157 9.045
23.861 1.530 1.363 0.000 21.89 7.77 23.76 Example 42 CoO-1 wt %
LSGMC 44.508 9.559 23.898 1.493 1.493 0.000 24.1 8.57 25.19 Example
43 CoO-2 wt % LSGMC 44.250 9.756 23.889 1.463 1.596 0.000 41.97
12.94 27.16 Example 44 CoO-3 wt % LSGMC 44.063 9.919 23.798 1.454
1.725 0.000 60.12 19.16 27.94 Example 45 CoO-4 wt % LSGMC 43.781
10.111 23.867 1.402 1.802 0.000 77.19 23.87 29.1 Example 46 CoO-5
wt % LSGMC 43.648 10.183 23.830 1.339 1.979 0.000 96.43 30.94 27.16
Comparative CoO-6 wt % LSGMC 43.469 10.297 23.830 1.287 2.106 0.000
120.69 38.49 26.17 Example 9 Example 47 Fe.sub.2O.sub.3-0.05 wt %
LSGMC 47.099 7.567 23.404 1.530 1.229 0.333 18.69 6.48 21.64
Example 48 Fe.sub.2O.sub.3-0.2 wt % LSGMC 49.045 7.652 23.347 1.491
1.180 0.547 19.46 7.88 23.79 Example 49 Fe.sub.2O.sub.3-1 wt %
LSGMC 49.177 5.909 23.038 1.465 1.143 0.635 22.16 8.57 25.94
Example 50 Fe.sub.2O.sub.3-2 wt % LSGMC 46.364 8.249 23.391 1.456
1.135 0.741 40.19 13.57 29.01 Example 51 Fe.sub.2O.sub.3-3 wt %
LSGMC 16.025 8.526 23.461 1.438 1.111 0.790 57.46 18.64 27.13
Example 52 Fe.sub.2O.sub.3-4 wt % LSGMC 45.834 8.685 23.515 1.408
1.062 0.887 77.16 23.94 26.43 Example 53 Fe.sub.2O.sub.3-5 wt %
LSGMC 45.499 8.964 23.587 1.379 1.013 0.984 94.61 30.84 25.13
Comparative Fe.sub.2O.sub.3-6 wt % LSGMC 43.442 9.168 23.598 1.361
0.964 1.106 110.67 36.19 24.36 Example 10 Example 54 NiO-0.05 wt %
LSGMC 46.675 7.968 23.339 1.515 1.233 0.526 19.44 6.55 20.49
Example 55 NiO-0.2 wt % LSGMC 46.257 8.423 23.159 1.512 1.214 0.831
21.06 7.61 23.14 Example 56 NiO-1 wt % LSGMC 45.703 8.905 23.211
1.497 1.167 0.961 22.73 8.48 25.37 Example 57 NiO-2 wt % LSGMC
45.173 9.347 23.307 1.480 1.120 1.039 40.59 13.4 28.33 Example 58
NiO-3 wt % LSGMC 44.610 9.842 23.284 1.455 1.073 1.273 57.49 18.29
27.11 Example 59 NiO-4 wt % LSGMC 44.221 10.213 23.319 1.438 1.025
1.404 75.49 25.64 26.34 Example 60 NiO-5 wt % LSGMC 43.280 11.043
23.341 1.425 1.006 1.592 93.87 31.59 25.09 Comparative NiO-6 wt %
LSGMC 42.653 11.586 23.400 1.388 0.958 1.779 112.49 36.49 23.16
Example 11
[0079]
4 TABLE 4 Content of element (wt %) Resistivity Resistivity
Strength Fe/Ni/Cu/Zn/ (.OMEGA. cm) at (.OMEGA. cm) at
(kgf/mm.sup.2) La Sr Ga Mg Co Mn 650.degree. C. 800.degree. C. at
R.T. Example 61 CuO-0.05 wt % LSGMC 46.758 7.888 23.351 1.493 1.232
0.596 18.49 7.16 21.46 Example 62 CuO-0.2 wt % LSGMC 46.567 8.093
23.284 1.476 1.210 0.788 21.78 7.94 23.11 Example 63 CuO-1 wt %
LSGMC 46.339 8.293 23.320 1.447 1.161 0.925 24.51 8.74 25.87
Example 64 CuO-2 wt % LSGMC 46.080 8.487 23.428 1.385 1.111 1.062
40.2 13.49 28.13 Example 65 CuO-3 wt % LSGMC 45.906 8.601 23.551
1.334 1.061 1.144 60.43 18.46 27.61 Example 66 CuO-4 wt % LSGMC
45.678 8.802 23.586 1.304 1.012 1.282 77.19 25.19 26 Example 67
CuO-5 wt % LSGMC 45.467 8.958 23.661 1.211 0.987 1.501 97.84 32.17
25.16 Comparative CuO-6 wt % LSGMC 45.216 9.156 23.745 1.150 0.938
1.667 109.49 37.94 24.31 Example 12 Example 68 ZnO-0.05 wt % LSGMC
47.523 7.401 22.902 1.545 1.257 0.865 19.99 6.51 21.06 Example 69
ZnO-0.2 wt % LSGMC 47.714 7.244 22.910 1.523 1.206 0.947 21.69 8.06
23.87 Example 70 ZnO-1 wt % LSGMC 48.042 7.016 22.838 1.511 1.104
1.142 24.1 8.74 25.64 Example 71 ZnO-2 wt % LSGMC 48.732 6.475
22.713 1.487 1.051 1.305 40.97 13.64 29.13 Example 72 ZnO-3 wt %
LSGMC 48.897 6.362 22.708 1.466 0.951 1.472 57.34 19.16 27.03
Example 73 ZnO-4 wt % LSGMC 48.970 6.282 22.776 1.423 0.900 1.553
77.18 24.31 26.13 Example 74 ZnO-5 wt % LSGMC 49.110 6.166 22.788
1.381 0.849 1.691 94.31 31.49 25.64 Comparative ZnO-6 wt % LSGMC
49.685 5.705 22.728 1.336 0.772 1.880 117.49 36.19 24.73 Example 13
Example 75 MnO-0.05 wt % LSGMC 46.949 7.636 23.566 1.509 1.203
0.257 18.97 5.98 20.94 Example 76 MnO-0.2 wt % LSGMC 46.838 7.806
23.451 1.482 1.131 0.539 21 7.67 23.43 Example 77 MnO-1 wt % LSGMC
46.551 8.090 23.396 1.455 1.108 0.728 22.74 8.4 25.7 Example 78
MnO-2 wt % LSGMC 46.354 8.295 23.357 1.437 1.060 0.894 42.16 13.64
28.69 Example 79 MnO-3 wt % LSGMC 46.064 8.533 23.451 1.397 0.986
1.013 57.34 18.7 27.08 Example 80 MnO-4 wt % LSGMC 45.869 8.691
23.533 1.346 0.911 1.156 75.73 25.19 26.31 Comparative MnO-5 wt %
LSGMC 45.518 8.968 23.657 1.286 0.836 1.299 105.68 30.98 25.99
Example 14
[0080] Evaluation
[0081] As can been seen from Tables 1 to 4, the mechanical
strengths of the oxide ion conductors of Examples 1 to 80 were
better than that of Comparative Example 1 which contains no metal
element B3. In addition, it was also confirmed that the
resistivities at a low temperature of 650.degree. C. of the oxide
ion conductors of Comparative Examples 2 to 14, which were out of
the ranges of the present invention, were increased to a level
approximately equivalent to that of 8-YSZ (8 mol %
Y.sub.2O.sub.3--ZrO.sub.2) at 650.degree. C. (approximately 120
.OMEGA..multidot.cm), which was used as a conventional oxide ion
conductor in practice, or the mechanical strengths were not
satisfactory improved.
[0082] Furthermore, as shown in FIG. 4, it was confirmed that the
matrix crystal grains of Comparative Example 1 composed of the
LSGMC, which contained no metal element B3, were larger than those
of Examples 4, 12, and 19, shown in FIGS. 1 to 3, and that the
first and the second crystal grains were present between the matrix
crystal grains shown in FIGS. 1 to 3. Hence, it is believed that
the mechanical strengths of Examples 4, 12, and 19 were improved.
It is also understood that the grain diameters of the first and the
second crystal grains were 0.1 to 2.0 .mu.m, and the volume
fractions thereof were 0.5 to 20 percent by volume.
[0083] As thus has been described, according to the present
invention, an oxide ion conductor can be obtained having oxide
ionic conduction higher than that of a stabilized zirconia, which
is a conventionally typical oxide ion conductor, and having a
relatively higher mechanical strength. Accordingly, the oxide ion
conductor of the present invention can be used at a lower
temperature than a stabilized zirconia. In addition, since the
oxide ion conductor of the present invention exhibits high oxide
ionic conductance at all oxygen partial pressures from an oxygen
atmosphere to a hydrogen atmosphere, the oxide ion conductor can be
effectively used as electrolytes for solid oxide fuel cells, gas
sensors, such as oxygen gas sensors, and oxygen separation
membranes for electrochemical oxygen pumps, whereby products having
performances superior to those of conventional products may be
produced.
[0084] According to the oxide ion conductor of the present
invention, the first crystal grains composed of elements Ln1, A,
and Ga and the second crystal grains composed of element B are
present between or in the matrix crystal grains other than the
first and the second crystal grains, the grain diameters of the
first and the second crystal grains are 0.1 to 2.0 .mu.m, the
volume fractions thereof are 0.5 to 20 percent by volume, and the
grain diameter of the matrix crystal grains is 2.0 to 7.0 .mu.m.
Accordingly, the oxide ion conductor of the present invention has a
relatively high mechanical strength, and in addition, the oxide ion
conductor maintains higher oxide ionic conduction in a wide range
of temperature and a wide range of oxygen partial pressure from an
oxygen atmosphere to a substantial hydrogen atmosphere, whereby the
oxide ion conductor of the present invention has significant
advantages.
[0085] This application claims priority under 35 U.S.C. .sctn. 119
to Japanese patent applications JP 2000-71759 filed on Mar. 15,
2000 and JP 2000-213659 filed on Jul. 14, 2000, which are
incorporated by references herein for its entirety.
* * * * *