U.S. patent application number 14/480790 was filed with the patent office on 2015-03-19 for methods to improve the performance of electrocaloric ceramic dielectric cooling device.
This patent application is currently assigned to Nascent Devices LLC. The applicant listed for this patent is Nascent Devices LLC. Invention is credited to Ailan Cheng.
Application Number | 20150075182 14/480790 |
Document ID | / |
Family ID | 52666696 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150075182 |
Kind Code |
A1 |
Cheng; Ailan |
March 19, 2015 |
METHODS TO IMPROVE THE PERFORMANCE OF ELECTROCALORIC CERAMIC
DIELECTRIC COOLING DEVICE
Abstract
A cooling device, which can cause cooling or heat-pumping,
comprising: multilayer electrocaloric ceramic modules as a
refrigerant where said modules are comprised of modified
BaTiO.sub.3 or bismuth based solid solution with PbTiO.sub.3,
wherein said modules have more than one ferroelectric phase in
generating an electrocaloric effect.
Inventors: |
Cheng; Ailan; (State
College, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nascent Devices LLC |
State College |
PA |
US |
|
|
Assignee: |
Nascent Devices LLC
State College
PA
|
Family ID: |
52666696 |
Appl. No.: |
14/480790 |
Filed: |
September 9, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61879418 |
Sep 18, 2013 |
|
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Current U.S.
Class: |
62/3.1 |
Current CPC
Class: |
F25B 2321/001 20130101;
H01L 37/025 20130101; F25B 21/00 20130101; Y02B 30/66 20130101;
Y02B 30/00 20130101 |
Class at
Publication: |
62/3.1 |
International
Class: |
F25B 21/00 20060101
F25B021/00 |
Claims
1. A cooling device, which can cause cooling or heat-pumping,
comprising: multilayer electrocaloric ceramic modules as a
refrigerant where said modules are comprised of modified
BaTiO.sub.3 or bismuth based solid solution with PbTiO.sub.3,
wherein said modules have more than one ferroelectric phase in
generating an electrocaloric effect.
2. The device of claim 1, wherein a ceramic layer in the multilayer
modules is thicker than 0.5
3. The device of claim 1, wherein: all ceramic layers in the
multilayer modules have the same ceramic composition and a
thickness, wherein the thickness of each ceramic layer is different
than a layer immediately adjacent to it.
4. The device of claim 1, wherein the composition of each ceramic
layer in the multilayer modules is different than one immediately
adjacent to it, so that one layer has a composition A and the next
layer has composition B and the resulting multilayer module has an
ABABAB structure.
5. The device of claim 1, wherein each ceramic layer in the
multilayer modules is selected from the group consisting of
Ba(Ti.sub.1-xSn.sub.x)O.sub.3where 0.08.ltoreq.x.ltoreq.0.20,
Ba(Ti.sub.1-xZr.sub.x)O.sub.3 where 0.1.ltoreq.x.ltoreq.0.25;
Ba(Ti.sub.1-xHf.sub.x)O.sub.3where 0.08.ltoreq.x.ltoreq.0.25,
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-yZr.sub.y)O.sub.3where 0.0823
x.ltoreq.0.2, and 0.1.ltoreq.y.ltoreq.0.25,
(Ba.sub.1-xSr.sub.x)TiO.sub.3 where 0.15.ltoreq.x.ltoreq.0.4,
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-ySn.sub.y)O.sub.3 where
0.1.ltoreq.x.ltoreq.0.3 and 0.05.ltoreq.y.ltoreq.0.3.
6. The ceramic layer of claim 5, further comprising a flux system,
said flux system comprising a glass-forming cation, a flux, an
A-site modifier and a B-site modifier, where: the glass-forming
cation is selected from the group consisting of B.sub.2O.sub.3,
SiO.sub.2, and GO.sub.2; the flux is selected from the group
consisting of PbO, BaO, SrO, and CaO; the A-site modifier is
selected from the group consisting of CdO, ZnO, Li.sub.2O, and CuO;
and the B-site modifier is selected from the group consisting of
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5.
7. The device of claim 5, wherein in Ba(Ti.sub.1-xSn.sub.x)O.sub.3,
0.1.ltoreq.x.ltoreq.0.15, in Ba(Ti.sub.1-xHf.sub.x)O.sub.3,
0.15.ltoreq.x.ltoreq.0.20 and in
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-yZr.sub.y)O.sub.3,
0.09.ltoreq.x.ltoreq.0.15 and 0.1.ltoreq.y.ltoreq.0.25.
8. The ceramic layer of claim 7, further comprising a flux system,
said flux system comprising a glass-forming cation, a flux, an
A-site modifier and a B-site modifier, where: the glass-forming
cation is selected from the group consisting of B.sub.2O.sub.3,
SiO.sub.2, and GeO.sub.2; the flux is selected from the group
consisting of PbO, BaO, SrO, and CaO; the A-site modifier is
selected from the group consisting of CdO, ZnO, Li.sub.2O, and CuO;
and the B-site modifier is selected from the group consisting of
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5.
9. The device of claim 1, wherein each ceramic layer in the
multilayer modules is selected from the group consisting of:
(Ba.sub.0.3Na.sub.0.7)(Ti.sub.0.3Nb.sub.0.7)O.sub.3,
Na.sub.0.5Bi.sub.0.5TiO.sub.3, (1-Y)
(Na.sub.0.5Bi.sub.0.5)TiO.sub.3-- y BaTiO.sub.3 where
0.1.ltoreq.y.ltoreq.0.9,
xBaTiO.sub.3-(1-x)((K.sub.1/2Na.sub.1/2)NbO.sub.3) where
0.1.ltoreq.x.ltoreq.0.9,
Ba(Zr.sub.xTi.sub.1-x)O.sub.3-y(Ba.sub.1-zCa.sub.z)TiO.sub.3 where
0.15.ltoreq.x.ltoreq.0.25, 0.2.ltoreq.z.ltoreq.0.4, and
0.2.ltoreq.y.ltoreq.0.4, xKNbO.sub.3--
(1-x)(BaTiO.sub.3--(Bi.sub.0.5Na.sub.0.5)TiO.sub.3) where
0.ltoreq.x.ltoreq.0.2.
10. The ceramic layer of claim 9, further comprising a flux system,
said flux system comprising a glass-forming cation, a flux, an
A-site modifier and a B-site modifier, where: the glass-forming
cation is selected from the group consisting of B.sub.2O.sub.3,
SiO.sub.2, and GeO.sub.2; the flux is selected from the group
consisting of PbO, BaO, SrO, and CaO; the A-site modifier is
selected from the group consisting of CdO, ZnO, Li.sub.2O, and CuO;
and the B-site modifier is selected from the group consisting of
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5.
11. The device of claim 1, wherein each ceramic layer in the
multilayer modules has the formula (1-x)BaTiO.sub.3-xR, where: R is
selected from the group consisting of LiTaO.sub.3, LiNbO.sub.3,
LiSbO.sub.3, SrHfO.sub.3, BaHfO.sub.3, CaHfO.sub.3, CaZrO.sub.3,
SrZrO.sub.3, (K.sub.0.5Bi.sub.0.5)TiO.sub.3,
(Na.sub.0.5Bi.sub.0.5)TiO.sub.3, (Li.sub.0.5Bi.sub.0.5)TiO.sub.3,
and their combinations, where 0.8<x<1 for LiTaO.sub.3,
LiNbO.sub.3, LiSbO.sub.3, where 0<x<0.5 for
(K.sub.0.5Bi.sub.0.5)TiO.sub.3, (Na.sub.0.5Bi.sub.0.5)TiO.sub.3,
(Li.sub.0.5Bi.sub.0.5)TiO.sub.3; and 0<x<0.5 for SrHfO.sub.3,
BaHfO.sub.3, CaHfO.sub.3, CaZrO.sub.3, SrZrO.sub.3.
12. The ceramic layer of claim 11, further comprising a flux
system, said flux system comprising a glass-forming cation, a flux,
an A-site modifier and a B-site modifier, where: the glass-forming
cation is selected from the group consisting of B.sub.2O.sub.3,
SiO.sub.2, and GeO.sub.2; the flux is selected from the group
consisting of PbO, BaO, SrO, and CaO; the A-site modifier is
selected from the group consisting of CdO, ZnO, Li.sub.2O, and CuO;
and the B-site modifier is selected from the group consisting of
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5.
13. The device of claim 1, wherein each ceramic layer in the
multilayer modules has the formula (1-x)BaTiO.sub.3-xR, where: R is
selected from the group consisting of
(K.sub.0.5Bi.sub.0.5)TiO.sub.3, (Na.sub.0.5Bi.sub.0.5)TiO.sub.3,
(Li.sub.0.5Bi.sub.0.5)TiO.sub.3, and their combinations, where
0<x<0.3.
14. The ceramic layer of claim 13, further comprising a flux
system, said flux system comprising a glass-forming cation, a flux,
an A-site modifier and a B-site modifier, where: the glass-forming
cation is selected from the group consisting of B.sub.2O.sub.3,
SiO.sub.2, and GeO.sub.2; the flux is selected from the group
consisting of PbO, BaO, SrO, and CaO; the A-site modifier is
selected from the group consisting of CdO, ZnO, Li.sub.2O, and CuO;
and the B-site modifier is selected from the group consisting of
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5.
15. The device of claim 1, wherein each ceramic layer in the
multilayer modules exhibits adiabatic temperature change of more
than 3.5.degree. C. under an applied electric field equal or less
than 15 MVm.
16. The device of claim 1, wherein each ceramic layer in the
multilayer modules exhibits adiabatic temperature change of more
than 4.degree. C. under an applied electric field of equal or less
than 15 MVm.
17. The device of claim 1, wherein each ceramic layer in the
multilayer modules exhibits adiabatic temperature change of more
than 4.5.degree. C. under an applied electric field equal or less
than 15 MVm.
18. The device of claim 1, wherein each ceramic layer in the
multilayer modules has a thickness greater than 1 .mu.m.
19. The ceramic layers of claim 1 are a bismuth based solid
solution with PbTiO.sub.3, (1-x)BiRO.sub.3-xPbTiO.sub.3, where: R
is selected from the group consisting of Fe, Mn, Cu, Sc, In, Ga,
Yb, Mg.sub.1/2Ti.sub.1/2, Zn.sub.1/2Ti.sub.1/2,
Co.sub.1/2Ti.sub.1/2, Mg.sub.1/2Zr.sub.1/2, Zn.sub.1/2Zr.sub.1/2,
Mg.sub.1/2Sn.sub.1/2, Mg.sub.2/3Nb.sub.1/3, Zn.sub.2/3Nb.sub.1/3,
Mg.sub.2/3Ta.sub.1/3, Zn.sub.2/3Nb.sub.1/3, Co.sub.2/3Nb.sub.1/3,
Co.sub.2/3Ta.sub.1/3, Mg.sub.3/4W.sub.1/4, Co.sub.3/4W.sub.1/4; and
0.05.ltoreq.x.ltoreq.0.95.
20. A cooling device, which can cause cooling or heat-pumping,
comprising: multilayer electrocaloric ceramic modules as a
refrigerant wherein said modules have more than one ferroelectric
phase in generating an electrocaloric effect and wherein each
ceramic layer in the multilayer modules has the formula La-modified
Pb(ZrTi)O.sub.3 ((PbLa.sub.x)(ZrTi)O.sub.3) where x is
0.08.ltoreq.x.ltoreq.0.12.
21. A cooling device, which can cause cooling or heat-pumping,
comprising: multilayer electrocaloric ceramic modules as a
refrigerant wherein said modules have more than one ferroelectric
phase in generating an electrocaloric effect and wherein each
ceramic layer in the multilayer modules has the formula
(1-x)ABO.sub.3+xPbTiO.sub.3, where: ABO.sub.3is selected from the
group consisting of Pb(Mg.sub.1/2W.sub.1/2)O.sub.3, where
0.4.ltoreq.x.ltoreq.0.65, Pb(Mg.sub.1/3Ta.sub.2/3)O.sub.3 where
0.3.ltoreq.x.ltoreq.0.5, Pb(Ni.sub.1/3Nb.sub.2/3)O.sub.3 where
0.3.ltoreq.x.ltoreq.0.5, Pb(Fe.sub.1/2Nb.sub.1/2)O.sub.3where
0.04.ltoreq.x.ltoreq.0.15, Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 where
0.25.ltoreq.x.ltoreq.0.45, Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3 where
0.05.ltoreq.x.ltoreq.0.2, Pb(Mn.sub.1/3Nb.sub.2/3)O.sub.3 where
0.15.ltoreq.x.ltoreq.to 0.35, Pb(Sc.sub.1/2Ta.sub.1/2)O.sub.3 where
0.35.ltoreq.x.ltoreq.0.55, Pb(Co.sub.1/3Nb.sub.2/3)O.sub.3 where
0.3.ltoreq.x.ltoreq.0.5, Pb(Sc.sub.1/2Nb.sub.1/2)O.sub.3 where
0.35.ltoreq.x.ltoreq.0.52, Pb(Co.sub.1/2W.sub.1/2)O.sub.3 where
0.35.ltoreq.x.ltoreq.0.55, Pb(In.sub.1/2Nb.sub.1/2)O.sub.3 where
0.30.ltoreq.x.ltoreq.0.45, Pb(Na.sub.1/2Bi.sub.1/2)O.sub.3 where
0.05.ltoreq.x.ltoreq.0.25, Pb(Yb.sub.1/2Nb.sub.1/2)O.sub.3 where
0.4.ltoreq.x.ltoreq.0.6, PbSnO.sub.3 where 0.3.ltoreq.x.ltoreq.0.5,
and PbHfO.sub.3 where 0.4.ltoreq.x .ltoreq.0.6.
22. A cooling device, which can cause cooling or heat-pumping,
comprising: multilayer electrocaloric ceramic modules as a
refrigerant wherein said modules have more than one ferroelectric
phase in generating an electrocaloric effect and wherein each
ceramic layer in the multilayer modules has the formula
(1-x)(K.sub.zNa.sub.yLi.sub.1-z-y)NbO.sub.3-- xAZrO.sub.3, where:
0<z<1; 0<y<1; 0.05.ltoreq.x.ltoreq.0.2; and A is
selected from the group consisting of Ca, Sr, and Ba.
23. The ceramic layer of claim 22, further comprising a flux
system, said flux system comprising a glass-forming cation, a flux,
an A-site modifier and a B-site modifier, where: the glass-forming
cation is selected from the group consisting of B.sub.2O.sub.3,
SiO.sub.2, and GeO.sub.2; the flux is selected from the group
consisting of PbO, BaO, SrO, and CaO; the A-site modifier is
selected from the group consisting of CdO, ZnO, Li.sub.2O, and CuO;
and the B-site modifier is selected from the group consisting of
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5.
24. The ceramic layer of claim 22 wherein Zr is substituted by a
zirconium composition selected from the group consisting of (ZrHf),
(ZrSn) and (ZrTi).
25. The ceramic layer of claim 24, further comprising a flux
system, said flux system comprising a glass-forming cation, a flux,
an A-site modifier and a B-site modifier, where: the glass-forming
cation is selected from the group consisting of B.sub.2O.sub.3,
SiO.sub.2, and GeO.sub.2; the flux is selected from the group
consisting of PbO, BaO, SrO, and CaO; the A-site modifier is
selected from the group consisting of CdO, ZnO, Li.sub.2O, and CuO;
and the B-site modifier is selected from the group consisting of
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5.
26. The flux of claim 25, wherein the amount of flux is less than 5
mol %.
Description
FIELD OF THE INVENTION
[0001] The present disclosure is directed to electrocaloric
ceramics and cooling devices, heat pumps, other devices employing
the same, and methods of making
BACKGROUND OF THE INVENTION
[0002] The electrocaloric effect has the potential to provide high
efficiency and environmentally friendly cooling technology,
especially if the effect is large. The electrocaloric effect (ECE)
is a result of direct coupling between the thermal properties, such
as entropy, and the electric properties, such as electric field and
polarization, in a dielectric material. In the ECE material, a
change in the applied electric field induces a corresponding change
in polarization, which in turn causes a change in the dipolar
entropy as measured by the isothermal entropy change .DELTA.S in
the dielectrics. If the electric field varies in an adiabatic
condition, the dielectric material will experience an adiabatic
temperature change .DELTA.T. To date, ECE materials having achieved
only a small ECE (.DELTA.T<2 K), near room temperature, is
commercially impractical for use in cooling devices.
[0003] Recently, it was demonstrated that by operating near
ferroelectric phase transitions, a giant EC response can be
realized (Bret Neese, Baojin Chu, Sheng-Guo Lu, Yong Wang, E.
Furman, and Q. M. Zhang, Large Electrocaloric Effect in
Ferroelectric Polymers Near Room Temperature. Science, 321,
821-823, 2008; S. G. Lu, B. Ro{hacek over (z)}i{hacek over (c)}, Q.
M. Zhang, Z. Kutnjak, Xinyu Li, E. Furman, Lee J. Gorny, Minren
Lin,B. Mali{hacek over (c)}, M. Kosec, R. Blinc, and R. Pirc.
Organic and Inorganic Relaxor Ferroelectrics with Giant
Electrocaloric Effect. Appl. Phys. Lett. 97, 162904, 2010). It has
also been shown that a giant ECE can be obtained by designing a
dielectric material near an invariant critical point (ICP), which
allows the coexistence of a large number of coexistence phases and
at which the energy barrier for the switching between different
phases is lowered markedly (see Z. K. Liu, Xinyu Li, and Q. M.
Zhang. Maximizing the number of coexisting phases near invariant
critical points for giant electrocaloric and electromechanical
responses in ferroelectrics. Appl. Phys. Lett.101, 082904
(2012)).
SUMMARY OF THE INVENTION
[0004] The advantages of the present disclosure include a cooling
device comprised of ceramic ECE materials with a large number of
co-existing phases. The ceramic EC modules are comprised of a
plurality of layers formed by two or more EC ceramic single layers.
The EC ceramic layers can be same or different materials. The
thickness of the EC layers may be the same or different.
[0005] These and other advantages are satisfied, in part, by a
cooling device comprising at least one high EC ceramic. The ceramic
materials include but are not limited to modified BaTiO.sub.3, such
as Ba(Ti.sub.1-xZr.sub.x)O.sub.3, Ba(Ti.sub.1-xSn.sub.x)O.sub.3,
Ba(Ti.sub.1-xHf.sub.x)O.sub.3,
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-xZr.sub.x)O.sub.3,
(Ba.sub.1-xSr.sub.x)TiO.sub.3,
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-ySn.sub.y)O.sub.3. The ceramic
material can be modified by varying the end member R in the formula
BaTiO.sub.3--R. The ceramic materials can also involve sintering to
expand the composition variables. Furthermore, the ceramic
materials can be La-modified Pb(ZrTi)O.sub.3
((PbLa.sub.x)(ZrTi)O.sub.3), and bismuth based solid solution with
PbTiO.sub.3 such as(1-x)BiRO.sub.3-xPbTiO.sub.3, where R is
selected from Fe, Mn, Cu, Sc, In, Ga, Yb, Mg.sub.1/2Ti.sub.1/2,
Zn.sub.1/2Ti.sub.1/2, Co.sub.1/2Ti.sub.1/2, Mg.sub.1/2Zr.sub.1/2,
Zn.sub.1/2Zr.sub.1/2, Mg.sub.1/2, Sn.sub.1/2, Mg.sub.2/3Nb.sub.1/3,
Zn.sub.2/3Nb.sub.1/3, Mg.sub.2/3Ta.sub.1/3, Zn.sub.2/3Nb.sub.1/3,
Co.sub.2/3Nb.sub.1/3, Co.sub.2/3Ta.sub.1/3, Mg.sub.3/4W.sub.1/4,
Co.sub.3/4W.sub.1/4 where 0.05.ltoreq.x.ltoreq.50.95. Of particular
interest for electrocaloric cooling are compositions near the
morphotropic boundary where a large number of phases may coexist
and large electrocaloric cooling was predicted theoretically and
was observed experimentally. For example the morphotropic boundary
of xPbTiO3-(1-x)Bi (Mg.sub.3/4W.sub.1/4)O.sub.3) is located
approximately at x=0.48. ICP also may lie near MPB although not
limited to MPB as pinch off type ICP are also known (see C.
Stringer et at Journal of Applied Physics, 97, 024101 (2005)).These
are a few examples of the materials. Many other modifications are
possible.
[0006] Additional advantages of the present invention will become
readily apparent to those skilled in this art from the following
detailed description, wherein only the preferred embodiment of the
invention is shown and described, simply by way of illustration for
carrying out the invention. As will be realized, the invention is
capable of other and different embodiments, and its several details
are capable of modifications in various respects, all without
departing from the invention. Accordingly, drawings and
descriptions are to be regarded as illustrative in nature, and not
as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Reference is made to the attached drawings, wherein elements
having the same reference numeral designations represent similar
elements throughout. Understanding that these drawings describe
only several embodiments of the disclosure and are, therefore, not
to be considered limiting of its scope and wherein:
[0008] FIG. 1. Schematic illustration of one embodiment of a
E-T-.sigma..sub.1-.sigma..sub.2-x.sub.PT-x.sub.PMmulti-dimensional
phase diagram with an ICP, using PM-PN-PT as an example with all
the phases reported presented (the labeling of the phases refers to
the zero-electric field phases). Here, x is the composition,
.sigma. a is stress, E is electric field and T is temperature. For
simplicity, x, .sigma., and E are drawn on the same axis. FIG. 2.
Phase diagram of one embodiment of Ba(Ti.sub.1-xZr.sub.x)O.sub.3,
showing an ICP at composition x near 0.2.
[0009] FIG. 3. Schematic phase diagram of one embodiment of
AZrO.sub.3modified (K.sub.zNa.sub.yLi.sub.1-z-y)NbO.sub.3 ceramics
(x(AZrO.sub.3)-(1-x)(K.sub.zNa.sub.yLi.sub.1-z-y)NbO.sub.3. Here,
0<z<1; 0<y<1; 0<x<1; A=Ca, Sr, Ba or the
combination thereof, and Zr can be substituted by the combination
of (ZrHf), (ZrSn), (ZrTi), but must include Zr.
[0010] FIG. 4. Schematic diagram of one embodiment of a ceramic
multilayer EC module. In the example, the multilayer has ABABAB . .
. sequence, where A (410) can be one ceramic composition and B
(420) can be another ceramic composition, both of them having a
large ECE; or A and B have the same composition but different
thickness. Although six ceramic layers are shown, the number of
ceramic layers in a multilayered EC module can be any number equal
or greater than 2.
DETAILED DESCRIPTION OFTHE INVENTION
[0011] One embodiment relates to ceramic EC materials having large
numbers of coexisting phases to achieve a large (.DELTA.T.gtoreq.2
K) electrocaloric effect (ECE). The advantages in some embodiments
are achieved by cooling devices comprised of ceramic ECE materials
with a large number of co-existing phases. The ceramic EC modules
are comprised of multilayers formed by two or more EC ceramic
single layers. The EC ceramic layers can be same or different. The
thickness of each EC layer may be the same or different.
[0012] These and other advantages are satisfied, in part, by a
cooling device comprising at least one high EC ceramic. In some
embodiments, the EC ceramic materials include but are not limited
to modified BaTiO.sub.3, e.g., Ba(Ti.sub.1-xZr.sub.x)O.sub.3,
Ba(Ti.sub.1-xSn.sub.x)O.sub.3, Ba(Ti.sub.1-xHf.sub.x)O.sub.3,
(Ba.sub.1-x,Sr.sub.x)(Ti.sub.1-xZr.sub.x)O.sub.3,
(Ba.sub.1-xSr.sub.x)TiO.sub.3,
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-ySn.sub.y)O.sub.3. In some
embodiments, the ceramic materials can also involve sintering aid
to expand the composition variables. In some embodiments, the
ceramic materials can be La-modified Pb(ZrTi)O.sub.3
((PbLa.sub.x)(ZrTi)O.sub.3) and bismuth based solid solution with
PbTiO.sub.3 such as (1-x)BiTiO.sub.3-xPbTiO.sub.3. These are a few
examples of the materials. Other modifications are possible.
[0013] Taking the ceramic
(PM.sub.y-PN.sub.1-y).sub.1-x-PT.sub.x(P=Pb, M=Mg, N=Nb, and T=Ti)
as an example, near the morphotropic phase boundary (x.about.0.3,
y.about.13), multiple phases (p.sub.max=6) could coexist near ICP
as illustrated in FIG. 1. FIG. 1 shows that multiple phases can
co-exist and energy barriers for the phase transformations near ICP
are low, thus leading to large EC responses. The disordered phase
(paraelectric phase) is a random mixture of a five ferroelectric
phases with local polarization directions randomly distributed
along symmetry allowed directions. For example, the five
ferroelectric phases can be rhombohedral (Rh), two monoclinic (M),
orthorhombic (O), tetragonal (T), and cubic. Using the entropy for
a ferroelectric phase, along with the concept of phase mixture
where a disordered paraelectric phase is considered as a random
mixture of various dipole orientations, the entropy of a dipolar
system can be written as
S dip = - i k v i c i ln ( c i / .OMEGA. i ) , ( Equation 1 )
##EQU00001##
where k is the Boltzmann constant, c.sub.i is the volume fraction
of the i.sup.th phase, .OMEGA..sub.i is the number of polar-states
in the i.sup.th phase, and v.sub.i is the average volume associated
with each dipolar unit in the i.sup.th phase (smallest unit of
v.sub.iis given by the volume per molecular unit). With Rh phase
(.OMEGA.=8), O phase (.OMEGA.=12), T phase (.OMEGA.=6), and two
monoclinic phases MC and MB (.OMEGA.=24 for both of them) in a
PM-PN-PT thin film near an ICP, and, for simplicity, c.sub.i=1/5
and v.sub.i=v.sub.0 is assumed for all the phases, Eq. 1 shows that
the entropy becomes Sdip=4.15k/v.sub.0, which is much larger
compared with a composition near pure PMN (pure Rh phase,
.OMEGA.=8), which has a Sdip=2.08k/v.sub.0. If a high electric
field can lead to a total saturation of polarization (.OMEGA.=1),
then Sdip(Emax)=0 can be obtained, and thus a much higher entropy
change .DELTA.S in EC response near ICP can be achieved. For the
example, here, .DELTA.Sdip(near ICP)/.DELTA.Sdip(Rh) is .about.2,
which is an enhancement of 100%. These predictions indeed have been
experimentally observed in the PMN-PT relaxor ceramics (Z. K. Liu,
Xinyu Li, and Q. M. Zhang. Appl. Phys. Lett. 101, 082904 (2012)).
For example, for P(MN).sub.1-x-PT.sub.x thin films at compositions
near pure PMN (for example, x<0.15), .DELTA.S in the range of
1.7 Jmol.sup.-1K.sup.-1 to 3.6 J mol.sup.-1K.sup.-1 was induced
under high electric fields (E=720 kV/m to 900 kV/m),while for
P(MN).sub.1-x-PT.sub.x thin films at composition near morphotropic
phase boundary (x.about.0.3), it was reported that a much higher
.DELTA.S from 3.7 Jmol.sup.-1K.sup.-1 to 8.7 J mol.sup.-K.sup.-1
was induced under fields in the range from 600 kV/m to 750 kV/m.
Here the average ratio .DELTA.S.sub.dip(near
ICP).DELTA.S.sub.dip(Rh)=2.3.
[0014] These results and considerations demonstrate the promise of
working with multi-phase and multi-component material systems near
ICPs to enhance the ECE. There are many material systems which can
exhibit such an ICP in which multi-phases can coexist (more than
two phases coexist). One class of dielectric ceramics which shows
large ECE is the modified BaTiO.sub.3 ceramics, which are lead-free
and hence are desirable because they are environmentally
friendly.
[0015] There are four different phases (rhombohedral (Rh),
orthorhombic (O), tetragonal (T), and cubic) in BaTiO.sub.3, with
phase transitions occurring at various temperatures as shown in
FIG. 2. When Zr concentration is at 15%, the system
BaZr.sub.xTi.sub.1-xO.sub.3exhibits a pinched phase transition,
i.e., all the above three phase transition temperatures (T1, T2 and
TC) correspond to pure BaTiO3 are merged or pinched into single
diffuse phase transition as shown in FIG. 2. The large number of
coexisting phases (4 different phases) at a single transition point
near room temperature indicates that a very large ECE at room
temperature can be obtained in this class of material.
[0016] The advantages of this embodiment is operating an EC
material near its ICP, wherein a maximum number of available phases
in the material can coexist and the energy barriers for switching
between different phases become vanishingly small (compared with
the thermal energy k.sub.BT, where k.sub.B is the Boltzmann
constant and T is the temperature in Kelvin). At room temperature
(300K), the thermal energy is 25 meV, leading to very large ECE.
One embodiment relates to modifying the composition to achieve
large ECE in modified BaTiO.sub.3(BTO) which possess ICP at certain
compositions. One example includes Ba(Ti.sub.1-xZr.sub.x)O.sub.3
for x in the range from 0.1 to 0.25, preferably from 0.15 to 0.20.
Other examples are environmentally friendly lead-free EC ceramics
with ICPs. These materials include but are not limited to
Ba(Ti.sub.1-xSn.sub.x)O.sub.3 for 0.08.ltoreq.x.ltoreq.0.20,
preferably 0.1.ltoreq.x.ltoreq.0.15, Ba(Ti.sub.1-xHf.sub.x)O.sub.3
for 0.08.ltoreq.x.ltoreq.0.25, preferably
0.15.ltoreq.x.ltoreq.0.20,
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-yZr.sub.y)O.sub.3 for composition
with 0.08.ltoreq.x.ltoreq.0.2, and preferably
0.09.ltoreq.x.ltoreq.0.15, and with 0.1.ltoreq.y.ltoreq.0.25,
(Ba.sub.1-xSr.sub.x)TiO.sub.3 where 0.15.ltoreq.x.ltoreq.0.4, and
(Ba.sub.1-xSr.sub.x)(Ti.sub.1-ySn.sub.y)O.sub.3where
0.1.ltoreq.x.ltoreq.0.3 and 0.05.ltoreq.y.ltoreq.0.3.
[0017] Another embodiment relates to flux systems often used in BTO
based ceramic materials to improve the sintering such as lowering
the sintering temperature while maintaining high dielectric
responses and obtaining good densification. Addition of flux
systems to BTO based ceramics also increase the number of possible
composition variables which can increase the possible number of
coexisting phases (see discussion of phase rule in the next
paragraph and in Z. K. Liu, Xinyu Li, and Q. M. Zhang. Appl. Phys.
Lett. 101, 082904 (2012)). These flux systems include glass-forming
flux such as B.sub.2O.sub.3, H.sub.3BO.sub.3, SiO.sub.2, and
GeO.sub.2, and flux such as PbO, BaO, SrO, MnO.sub.2,
Li.sub.2O.sub.3, LiBiO.sub.2 and CaO which are very soluble in the
lattice, and CdO, ZnO, Li.sub.2O,CuO, BaO, SrO, CaO, Na.sub.2O,
K.sub.2O, and Bi.sub.2O.sub.3 which are the A-site modifiers, and
Bi.sub.2O.sub.3, Y.sub.2O.sub.3, Sb.sub.2O.sub.5, WO.sub.3, and
Nb.sub.2O.sub.5 which are B-site modifiers. These two types of
modifiers (A-site and B-site) have limited solubility in the
ceramic lattice (<5 mol %). Other lead-free ceramics such
as(Ba.sub.0.3Na.sub.0.7)(Ti.sub.0.3Nb.sub.0.7)O.sub.3,
Na.sub.0.5Bi.sub.0.5TiO.sub.3,
(1-y)(Na.sub.0.5Bi.sub.0.5)TiO.sub.3-y BaTiO.sub.3 where
0.1.ltoreq.y .ltoreq.0.9,
xBaTiO.sub.3-(1-x)((K.sub.1/2Na.sub.1/2)NbO.sub.3) where
0.1.ltoreq.x.ltoreq.0.9, and SrBiTa.sub.2O.sub.9can also exhibit
multiphase co-existence region, leading to large ECE.
[0018] From thermodynamics consideration, the number of co-existing
phases is constrained not only by the number of the available
phases, but also by the variables such as the compositions,
chemical potentials, temperature, stresses, and electrical field.
For the material of two compositions, such as
Ba(Zr.sub.xTi.sub.1-x)O.sub.3, composition x, temperature and
electric field perpendicular to the ceramic layers are all
variables. The number of maximum coexistence phases p.sub.max is 3
(p.sub.max=m+v-f), where m is the independent composition variable,
v is the all possibly available other variables including
temperature, stresses, and electrical field, and f is the fixed
variable which can't be changed for the material system. Taking
Ba(Zr.sub.xTi.sub.1-x)O.sub.3 ceramic as an example, m=1 (since the
composition x can be varied),available variables for v include 6
for stresses, 3 for electrical field and one for temperature, thus,
v=10, and fixed variable f=8 (6 for stresses (stress=0) since the
material is in room pressure which is fixed, and 2 for electric
field since ceramics are isotropic material. In order to induce a
4-phase coexistence point, one needs to introduce one more
composition variable or other variables.
[0019] Another embodiment relates to using the flux to serve as
additional variables to accommodate more phases to coexist. The
flux can be added to the ceramics to increase the composition
variables and improve the sintering. These include the
glass-forming flux such as B.sub.2O.sub.3, SiO.sub.2, and
GeO.sub.2, the flux such as PbO, BaO, SrO, and CaO which are very
soluble in the lattice, and CdO, ZnO, Li.sub.2O, and CuO which are
the A-site modifiers, and Bi.sub.2O.sub.3, Y.sub.2O.sub.35
Sb.sub.2O.sub.55 WO.sub.3, and Nb.sub.2O.sub.5 which are B-site
modifiers.
[0020] Another embodiment relates to mixing different ceramics to
increase the number of variables. Examples include but not limited
to
(1-y)Ba(Zr.sub.xTi.sub.1-x)O.sub.3-y(Ba.sub.1-zCa.sub.z)TiO.sub.3where
0.1523 x.ltoreq.0.25, z in the range from 0.2.ltoreq.z.ltoreq.0.4,
and 0.2.ltoreq.y.ltoreq.0.4, and xKNbO.sub.3-- (1-x)(BaTiO.sub.3--
(Bi.sub.0.5Na.sub.0.5)TiO.sub.3) where 0.ltoreq.x.ltoreq.0.2. The
large number of composition variables will increase the number of
possible coexisting phases and lead to larger ECE. This approach
can also be applied to other ceramics.
[0021] Another embodiment relates to polar-ceramic systems of
(1-x)(K.sub.zNa.sub.yLi.sub.1-z-y)NbO.sub.3 (0<z<1;
0<y<1, 0<x<l)-xAZrO.sub.3, wherein A=Ca, Sr, Ba or the
combination thereof, wherein Zr can be the combination of (ZrHf),
(ZrSn) and(ZrTi)and must include Zr. These ceramics also possess
similar ICP behavior (see FIG. 3) and can exhibit a large ECE.
Another embodiment relates to increasing the number of co-existing
phases near ICP of lead-based ceramics to enhance the ECE. These
lead-based ceramics include, for example, La-modified
Pb(Zr.sub.xTi.sub.1-x)O.sub.3 where 0.3.ltoreq.x.ltoreq.0.7, to
enhance the ECE. The forming of solid solution from different
ceramics to increase the variables so that a large number of phases
can coexist will also be used here. The ceramics that exhibit ICP
and have promise to achieve ECE include solid solutions with
PbTiO.sub.3. For these ceramics, there exist cubic, rhombohedral,
orthorhombic and tetragonal phases at certain composition, in
addition there exist four-phase coexistent composition regions near
ICP. The solid solutions with PbTiO.sub.3can be expressed in
(1-x)ABO.sub.3+xPbTiO.sub.3, where ABO.sub.3 includes
Pb(Mg.sub.1/2W.sub.1/2)O.sub.3 with 0.4.ltoreq.x.ltoreq.0.65,
Pb(Mg.sub.1/3Ta.sub.2/3)O.sub.3 with 0.3.ltoreq.x.ltoreq.0.5,
Pb(Ni.sub.1/3Nb.sub.2/3)O.sub.3 with 0.3.ltoreq.x.ltoreq.0.5,
Pb(Fe.sub.1/2Nb.sub.1/2)O.sub.3 with 0.04.ltoreq.x.ltoreq.0.15,
Pb(Mg.sub.1/3Nb.sub.2/3)O.sub.3 with 0.25.ltoreq.x.ltoreq.0.45,
Pb(Zn.sub.1/3Nb.sub.2/3)O.sub.3 with 0.05.ltoreq.x.ltoreq.0.2,
Pb(Mn.sub.1/3Nb.sub.2/3)O.sub.3 with 0.15.ltoreq.x.ltoreq.0.35,
Pb(Sc.sub.1/2Ta.sub.1/2)O.sub.3 with 0.35.ltoreq.x.ltoreq.0.55,
Pb(Co.sub.1/3Nb.sub.2/3)O.sub.3 with 0.3.ltoreq.x.ltoreq.0.5,
Pb(Sc.sub.1/2Nb.sub.1/2)O.sub.3 with 0.35.ltoreq.x.ltoreq.0.52,
Pb(Co.sub.1/2W.sub.1/2)O.sub.3 with 0.35.ltoreq.x.ltoreq.0.55,
Pb(In.sub.1/i2Nb.sub.1/2)O.sub.3 with 0.30.ltoreq.x.ltoreq.0.45,
Pb(Na.sub.1/2 Bi.sub.1/2)O.sub.3 with 0.05.ltoreq.x.ltoreq.0.25,
Pb(Yb.sub.1/2Nb.sub.1/2)O.sub.3 with 0.4.ltoreq.x.ltoreq.0.6,
PbSnO.sub.3 with 0.3.ltoreq.x.ltoreq.0.5, and PbHfO.sub.3 with
0.4.ltoreq.x.ltoreq.0.6.
[0022] Another embodiment of this disclosure is bismuth based solid
solution with PbTiO.sub.3. These materials have the potential to
have a large number of co-existing phases near ICP, thus, to have a
high ECE. These ceramics include but not limited to
(1-x)BiRO.sub.3-xPbTiO.sub.3, where R is selected from Fe, Mn, Cu,
Sc, In, Ga, Yb, Mg.sub.1/2Ti.sub.1/2, Co.sub.1/2Ti.sub.1/2,
Mg.sub.1/2Zr.sub.1/2, Zn.sub.1/2Zr.sub.1/2, Mg.sub.1/2Sn.sub.1/2,
Mg.sub.2/3Nb.sub.1/3, Zn.sub.2/3Nb.sub.1/3, Mg.sub.2/3Ta.sub.1/3,
Zn.sub.2/3Nb.sub.1/3, Co.sub.2/3Nb.sub.1/3, Co.sub.2/3Ta.sub.1/3,
Mg.sub.3/4W.sub.1/4, Co.sub.3/4W.sub.1/4, where
0.05.ltoreq.x.ltoreq.0.95.
[0023] Another embodiment of this invention is to use multilayers
to introduce additional variables (stresses and electric fields) to
increase the number of coexistence phases, as illustrated in FIG.
3. In the example illustrated, there are two types of EC ceramics A
and B, A is, for example, BaTi.sub.0.85Zr.sub.0.15O.sub.3, and B is
BaTi.sub.0.5Zr.sub.0.2O.sub.3. Ceramics A and B can be fabricated
into multilayers with proper sintering aids.
[0024] Another embodiment of this invention is to fabricate the EC
element in multilayer form, as illustrated in FIG. 4. Since the EC
response of EC ceramics is related to the applied electric field on
each EC layer. The relationship between the electric field (E),
voltage (V) and thickness (d) of the ceramic is E=V/d. Thin EC
layer in the multilayer can reduce the operation voltage while
maintaining the required electric field. For example, for a
multilayer EC element (or module) with each EC layer 5 .mu.m thick,
an applied voltage of 100 V will induce a 20 MV/m electric field in
each EC ceramic layer. In addition, thin ceramic layer (less than
10 .mu.m, for example) displays higher dielectric strength than
that of a thick ceramic layer (100 .mu.m, for example). In general,
the thickness of each EC layer in a multilayer EC module can range
1 .mu.m to 100 .mu.m or thicker. The maximum number of layers can
be 100, 200 or even 1000.
Only the preferred embodiment of the present invention and examples
of its versatility are shown and described in the present
disclosure. It is to be understood that the present invention is
capable of use in various other combinations and environments and
is capable of changes or modifications within the scope of the
inventive concept as expressed herein. Thus, for example, those
skilled in the art will recognize, or be able to ascertain, using
no more than routine experimentation, numerous equivalents to the
specific substances, procedures and arrangements described herein.
Such equivalents are considered to be within the scope of this
invention, and are covered by the following claims.
* * * * *