Thermoelectric conversion material and producing method thereof, and thermoelectric conversion element using the same

Abstract

Thermoelectric conversion materials, expressed by the following formula: Bi.sub.1-xM.sub.xCu.sub.1-wO.sub.a-yQ1.sub.yTe.sub.b-zQ2.sub.z. Here, M is at least one element selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Mn, Ga, In, Tl, As and Sb; Q1 and Q2 are at least one element selected from the group consisting of S, Se, As and Sb; x, y, z, w, a, and b are 0x<1, 0<w<1, 0.2<a<4, 0y<4, 0.2<b<4, 0z<4 and x+y+z>0. These thermoelectric conversion materials may be used for thermoelectric conversion elements, where they may replace thermoelectric conversion materials in common use, or be used along with thermoelectric conversion materials in common use.

Claims

1. Thermoelectric conversion materials, expressed by the following formula 1:
Bi.sub.1-xM.sub.xCu.sub.1-wO.sub.a-yQ1.sub.yTe.sub.b-zQ2.sub.zFormula 1 where M is at least one element selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Mn, Ga, In, Tl, As and Sb; Q1 and Q2 are at least one element selected from the group consisting of S, Se, As and Sb; x, y, z, w, a, and b are 0x<1, 0<w<1, 0.2<a<4, 0y<4, 0.2<b<4, 0z<4, b>z and x+y+z>0.

2. The thermoelectric conversion materials according to claim 1, wherein x, y and z of the formula 1 are respectively 0x1/2, 0ya/2 and 0zb/2.

3. The thermoelectric conversion materials according to claim 1, wherein a, y, b and z of the formula 1 are respectively a=1, 0y<1, b=1 and 0z<1.

4. The thermoelectric conversion materials according to claim 3, wherein x, w, a, y, b and z of the formula 1 are respectively 0x<0.15, 0w<0.2, a=1, 0y<0.2, b=1 and 0z<0.5.

5. The thermoelectric conversion materials according to claim 3, wherein M of the formula 1 is any one selected from the group consisting of Sr, Cd, Pb and Tl.

6. The thermoelectric conversion materials according to claim 3, wherein Q1 and Q2 of the formula 1 are respectively Se or Sb.

7. The thermoelectric conversion materials according to claim 3, wherein x, w, a, y, b and z of the formula 1 are respectively 0x<0.15, 0<w0.2, a=1, 0y<0.2, b=1 and 0z<0.5; M is any one selected from the group consisting of Sr, Cd, Pb and Tl; Q1 and Q2 are respectively Se or Sb.

8. The thermoelectric conversion materials according to claim 7, wherein x, a, y, b and z of the formula 1 are respectively 0<x<0.15, a=1, y=0, b=1 and z=0.

9. The thermoelectric conversion materials according to claim 7, wherein x, y and z of the formula 1 are respectively x=0, a=1, y=0, b=1 and 0<z0.5.

10. A method for producing thermoelectric conversion materials, wherein Bi.sub.2O.sub.3, Bi, Cu, Te, and at least one selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Mn, Ga, In, Tl, As and Sb, or their oxides, are mixed and then sintered to produce the thermoelectric conversion materials expressed by the formula 1 in the claim 1.

11. The method for producing thermoelectric conversion materials according to claim 10, wherein the sintering process is executed at a temperature of 400 to 570 C.

12. A method for producing thermoelectric conversion materials, wherein Bi.sub.2O.sub.3, Bi, Cu, and Te are mixed with at least one selected from the group consisting of S, Se, As and Sb, or their oxides, and then at least one selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Mn, Ga, In, Tl, As and Sb, or their oxides, are selectively further mixed thereto and then sintered to produce the thermoelectric conversion materials expressed by the formula 1 in the claim 1.

13. The method for producing thermoelectric conversion materials according to claim 12, wherein the sintering process is executed at a temperature of 400 to 570 C.

14. A thermoelectric conversion element, which includes the thermoelectric conversion materials defined in claim 1.

Description

DESCRIPTION OF DRAWINGS

(1) Other objects and aspects of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawing in which:

(2) FIG. 1 shows Rietveld refinement profiles for BiCuOTe, comparing X-ray diffraction pattern with a calculated pattern from a structural model;

(3) FIG. 2 shows the crystal structure of BiCuOTe;

(4) FIG. 3 shows X-ray diffraction pattern of BiCu.sub.0.9OTe;

(5) FIG. 4 shows Rietveld refinement profiles for Bi.sub.0.98Pb.sub.0.02CuOTe, comparing X-ray diffraction pattern with a calculated pattern from a structural model;

(6) FIG. 5 shows the crystal structure of Bi.sub.0.98Pb.sub.0.02CuOTe;

(7) FIG. 6 shows X-ray diffraction pattern of Bi.sub.0.9Pb.sub.0.1CuOTe;

(8) FIG. 7 shows X-ray diffraction pattern of Bi.sub.0.9Cd.sub.0.1CuOTe;

(9) FIG. 8 shows X-ray diffraction pattern of Bi.sub.0.9Sr.sub.0.1CuOTe;

(10) FIG. 9 shows Rietveld refinement profiles for BiCuOSe.sub.0.5Te.sub.0.5, comparing X-ray diffraction pattern with a calculated pattern from a structural model;

(11) FIG. 10 shows the crystal structure of BiCuOSe.sub.0.5Te.sub.0.5;

(12) FIG. 11 shows X-ray diffraction pattern of Bi.sub.0.9Tl.sub.0.1CuOTe;

(13) FIG. 12 shows X-ray diffraction pattern of BiCuOTe.sub.0.9Sb.sub.0.1;

(14) FIG. 13 shows electrical conductivities, Seebeck coefficients, thermal conductivities, and ZT values of BiCuOTe at different temperatures;

(15) FIG. 14 shows electrical conductivities, Seebeck coefficients, thermal conductivities, and ZT values of Bi.sub.0.9Sr.sub.0.1CuOTe at different temperatures;

(16) FIG. 15 shows electrical conductivities, Seebeck coefficients, thermal conductivities, and ZT values of Bi.sub.0.9Cd.sub.0.1CuOTe at different temperatures;

(17) FIG. 16 shows electrical conductivities, Seebeck coefficients, thermal conductivities, and ZT values of Bi.sub.0.9Pb.sub.0.1CuOTe at different temperatures;

(18) FIG. 17 shows electrical conductivities, Seebeck coefficients, thermal conductivities, and ZT values of Bi.sub.0.98Pb.sub.0.02CuOTe at different temperatures; and

(19) FIG. 18 shows electrical conductivities, Seebeck coefficients, thermal conductivities, and ZT values of Bi.sub.0.9Tl.sub.0.1CuOTe at different temperatures.

(20) FIG. 19 shows electrical conductivities, Seebeck coefficients, thermal conductivities, and ZT values of Bi.sub.0.95Pb.sub.0.05Cu.sub.0.960 Te.sub.0.95Se.sub.0.05 at different temperatures.

BEST MODE

(21) Compositions of the thermoelectric conversion materials of the present invention are expressed by the following formula 1.
Bi.sub.1-xM.sub.xCu.sub.1-wO.sub.a-yQ1.sub.yTe.sub.b-zQ2.sub.zFormula 1

(22) In the formula 1, M is at least one element selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Mn, Ga, In, Tl, As and Sb, and Q1 and Q2 are at least one element selected from the group consisting of S, Se, As and Sb with 0x<1, 0<w<1, 0.2<a<4, 0y<4, 0.2<b<4, 0z<4 and x+y+z>0.

(23) In the formula 1, x, y, and z are preferably 0x, 0ya/2 and 0zb/2, respectively.

(24) In the formula 1, a, y, b and z of the formula 1 are preferably a=1, 0y<1, b=1 and 0z<1, respectively. In other cases, x, w, a, y, b and z may be respectively 0x<0.15, 0<w0.2, a=1, 0y<0.2, b=1 and 0z<0.5. Here, M is preferably any one selected from the group consisting of Sr, Cd, Pb and Tl, and Q1 and Q2 are preferably Se or Sb, respectively.

(25) For the thermoelectric conversion materials of the formula 1, it is more preferred that x, a, y, b and z of the formula 1 are respectively 0<x<0.15, a=1, y=0, b=1 and z=0, and M is any one selected from the group consisting of Sr, Cd, Pb and Tl. In addition, in the formula 1 where x, a, y, b and z of the formula 1 are respectively x=0, a=1, y=0, b=1 and 0<z0.5, and Q2 is Se or Sb.

(26) Meanwhile, the thermoelectric conversion materials expressed by the formula 1 may be produced by mixing powders of Bi.sub.2O.sub.3, Bi, Cu and Te and then vacuum-sintering the mixture, but the present invention is not limited thereto.

(27) Also, the thermoelectric conversion materials expressed by the formula 1 may be produced by heating mixtures of Bi.sub.2O.sub.3, Bi, Cu, Te, and at least one selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Mn, Ga, In, Tl, As and Sb, or their oxides in an evacuated silica tube, however the present invention is not limited thereto.

(28) In addition, the thermoelectric conversion materials expressed by the formula 1 may be produced by heating mixtures of Bi.sub.2O.sub.3, Bi, Cu, Te, at least one element selected from the group consisting of S, Se, As and Sb, or their oxides, and optionally at least one selected from the group consisting of Ba, Sr, Ca, Mg, Cs, K, Na, Cd, Hg, Sn, Pb, Mn, Ga, In, Tl, As, and Sb, or their oxides in an evacuated silica tube, however the present invention is not limited thereto.

(29) The thermoelectric conversion materials of the present invention may be produced by sintering mixtures in a flowing gas such as Ar, He or N.sub.2, which partially includes hydrogen or does not include hydrogen. The sintering process is preferably executed at a temperature of 400 to 750 C., more preferably 400 to 570 C.

MODE FOR INVENTION

(30) Hereinafter, the preferred embodiment of the present invention will be described in detail based on examples. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention should not be interpreted as being limited to the examples. The embodiments of the present invention are provided just for explaining the present invention more perfectly to those having ordinary skill in the art.

Example 1

BiCuOTe

(31) In order to prepare BiCuOTe, 1.1198 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.5022 g of Bi (Aldrich, 99.99%, <10 m), 0.4581 g of Cu (Aldrich, 99.7%, 3 m), and 0.9199 g of Te (Aldrich, 99.99%, 100 mesh) were well mixed by using agate mortar, and then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining BiCuOTe powder.

(32) The powder X-ray diffraction (XRD) data were collected at room temperature on a Bragg-Brentano diffractometer (Bruker Advance D8 XRD) with a Cu X-ray tube (=1.5406 , 50 kV, 40 mA). The step size was 0.02 degree.

(33) TOPAS program (R. W. Cheary, A. Coelho, J. Appl. Crystallogr. 25 (1992) 109-121; Bruker AXS, TOPAS 3, Karlsruhe, Germany (2000)) was used in order to determine the crystal structure of the obtained material. The analysis results are shown in Table 1 and FIG. 2.

(34) TABLE-US-00001 TABLE 1 Atom site x y z Occup. Beq Bi 2c 0.25 0.25 0.37257(5) 1 0.56(1) Cu 2a 0.75 0.25 0 1 0.98(3) O 2b 0.75 0.25 0.5 1 0.26(12) Te 2c 0.25 0.25 0.81945(7) 1 0.35(1)

(35) Crystallographic data obtained from Rietveld refinement of BiCuOTe [Space group I4/nmm (No. 129), a=4.04138(6) , c=9.5257(2) ]

(36) FIG. 1 shows a Rietveld refinement profile that compares observed X-ray diffraction pattern of BiCuOTe with a calculated X-ray diffraction pattern from a structural model. FIG. 1 shows that the measured pattern well agrees with the calculated pattern according to Table 1, which implies that the material obtained in this example is BiCuOTe.

(37) As shown in FIG. 2, the BiCuOTe exhibits a natural super-lattice structure in which Cu.sub.2Te.sub.2 layers and Bi.sub.2O.sub.2 layers are repeated along a c-crystalline axis. Also, it can be said that BiTeCu layers and O layers are repeated along the c-crystalline axis in the natural super-lattice structure.

Example 2

BiCu0.9OTe

(38) In order to prepare BiCu.sub.0.9OTe, 1.1371 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.51 g of Bi (Aldrich, 99.99%, <10 m), 0.4187 g of Cu (Aldrich, 99.7%, 3 m), and 0.9342 g of Te (Aldrich, 99.99%, 100 mesh) were well mixed by using agate mortar, and then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining BiCu.sub.0.9TeO powder.

(39) X-ray diffraction analysis was conducted for the sample in the same way as the example 1. As shown in FIG. 3, the material obtained in the example 2 was identified as BiCu.sub.0.9TeO.

Example 3

Bi0.98Pb0.02CuOTe

(40) In order to prepare Bi.sub.0.98Pb.sub.0.02CuOTe, 2.5356 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 1.1724 g of Bi (Aldrich, 99.99%, <10 m), 1.0695 g of Cu (Aldrich, 99.7%, 3 m), 0.0751 g of PbO (Canto, 99.5%), and 2.1475 g of Te (Aldrich, 99.99%, 100 mesh) were well mixed by using agate mortar, and then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining Bi.sub.0.98Pb.sub.0.02CuOTe powder.

(41) The powder X-ray diffraction (XRD) data were collected at room temperature on a Bragg-Brentano diffractometer (Bruker D4-Endeavor XRD) with a Cu X-ray tube (=1.5406 , 50 kV, 40 mA). The step size was 0.02 degree.

(42) TOPAS program (R. W. Cheary, A. Coelho, J. Appl. Crystallogr. 25 (1992) 109-121; Bruker AXS, TOPAS 3, Karlsruhe, Germany (2000)) was used in order to determine the crystal structure of the obtained material. The analysis results are shown in Table 2 and FIG. 5.

(43) TABLE-US-00002 TABLE 2 Atom site x y z Occup. Beq. Bi 2c 0.25 0.25 0.37225(12) 0.98 0.59(4) Pb 2c 0.25 0.25 0.37225(12) 0.02 0.59(4) Cu 2a 0.75 0.25 0 1 1.29(10) O 2b 0.75 0.25 0.5 1 0.9(4) Te 2c 0.25 0.25 0.81955(17) 1 0.55(5)
Crystallographic data obtained from Rietveld refinement of Bi.sub.0.98Pb.sub.0.02CuOTe [Space group P4/nmm (No. 129), a=4.04150(4) , c=9.53962(13) ]

(44) FIG. 4 shows a Rietveld refinement profile that compares observed X-ray diffraction pattern of Bi.sub.0.98Pb.sub.0.02CuOTe with calculated pattern of a structural model. FIG. 4 shows that the measured pattern well agrees with the calculated pattern according to Table 2, which implies that the material obtained in this example is Bi.sub.0.98Pb.sub.0.02CuOTe.

(45) As shown in FIG. 5, the Bi.sub.0.98Pb.sub.0.02CuOTe exhibits a natural super-lattice structure in which Cu.sub.2Te.sub.2 layers and (Bi,Pb).sub.2O.sub.2 layers where Pb is partially substituted in place of Bi are repeated along a c-crystalline axis. Also, it can be said that (Bi,Pb)TeCu layers and O layers are repeated along the c-crystalline axis in the natural super-lattice structure.

Example 4

Bi0.9Pb0.1CuOTe

(46) In order to prepare Bi.sub.0.9Pb.sub.0.1CuOTe, 1.2721 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.6712 g of Bi (Aldrich, 99.99%, <10 m), 0.6133 g of Cu (Aldrich, 99.7%, 3 m), 0.215 g of PbO (Canto, 99.5%), and 1.2294 g of Te (Aldrich, 99.99%, 100 mesh) were well mixed by using agate mortar, and then heated in an evacuated silica tube at 510 r for 15 hours, thereby obtaining Bi.sub.0.9Pb.sub.0.1CuOTe powder.

(47) X-ray diffraction analysis was conducted for the sample in the same way as the example 3. As shown in FIG. 6, the material obtained in the example 4 was identified as Bi.sub.0.9Pb.sub.0.1CuOTe.

Example 5

Bi0.9Cd0.1CuOTe

(48) In order to prepare Bi.sub.0.9Cd.sub.0.1CuOTe, 1.3018 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.6869 g of Bi (Aldrich, 99.99%, <10 m), 0.6266 g of Cu (Aldrich, 99.7%, 3 m), 0.1266 g of CdO (Strem, 99.999%), and 1.2582 g of Te (Aldrich, 99.99%, 100 mesh) were well mixed by using agate mortar, and then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining Bi.sub.0.9Cd.sub.0.1CuOTe powder.

(49) X-ray diffraction analysis was conducted for the sample in the same way as the example 3. As shown in FIG. 7, the material obtained in the example 5 was identified as Bi.sub.0.9Cd.sub.0.1CuOTe.

Example 6

Bi0.9Sr0.1CuOTe

(50) In order to prepare Bi.sub.0.9Sr.sub.0.1CuOTe, 1.0731 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.5662 g of Bi (Aldrich, 99.99%, <10 m), 0.5165 g of Cu (Aldrich, 99.7%, 3 m), 1.0372 g of Te (Aldrich, 99.99%, 100 mesh), and 0.0842 g of SrO were well mixed by using agate mortar. Here, SrO was obtained by thermally treating SrCO.sub.3 (Alfa, 99.994%) at 1125 C. for 12 hours in the air. The material obtained by thermal treatment was confirmed as SrO by X-ray diffraction analysis.

(51) The mixture was then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining Bi.sub.0.9Sr.sub.0.1CuOTe powder.

(52) The powder X-ray diffraction (XRD) data were collected at room temperature on a Bragg-Brentano diffractometer (Bruker D8 Advance XRD) with a Cu X-ray tube (=1.5406 , 50 kV, 40 mA). The step size was 0.02 degree. FIG. 8 shows that the material obtained in the example 6 is Bi.sub.0.9Sr.sub.0.1CuOTe.

Example 7

BiCuOSe0.5Te0.5

(53) In order to prepare BiCuOSe.sub.0.5Te.sub.0.5, 1.9822 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.889 g of Bi (Aldrich, 99.99%, <10 m), 0.811 g of Cu (Aldrich, 99.7%, 3 m), 0.5036 g of Se (Aldrich, 99.99%), and 0.8142 g of Te (Aldrich, 99.99%, 100 mesh) were well mixed by using agate mortar, and then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining BiCuOSe.sub.0.5Te.sub.0.5 powder.

(54) The powder X-ray diffraction (XRD) data were collected at room temperature on a Bragg-Brentano diffractometer (Bruker D4-Endeavor XRD) with a Cu X-ray tube (40 kV, 40 mA). The step size was 0.02 degree. At this time, variable 6 mm slit was used as a divergence slit. The results are shown in FIG. 9. Crystal structure analysis was executed in the same way as the example 3. The analysis results are shown in Table 3 and FIG. 10.

(55) TABLE-US-00003 TABLE 3 Atom site x y z Occup. Beq. Bi 2c 0.25 0.25 0.36504(9) 1 0.86(2) Cu 2a 0.75 0.25 0 1 2.00(9) O 2b 0.75 0.25 0.5 1 1.9(3) Te 2c 0.25 0.25 0.82272(14) 0.5 0.61(4) Se 2c 0.25 0.25 0.82252(14) 0.5 0.55(5)
Crystallographic data obtained from Rietveld refinement of BiCuOSe.sub.0.5Te.sub.0.5 [Space group P4/nmm (No. 129), a=3.99045(11) , c=9.2357(4) ]

(56) FIG. 9 shows that the measured pattern well agrees with the calculated pattern from the results in Table 3, and as a result the material obtained in this example is identified as BiCuOSe.sub.0.5Te.sub.0.5.

(57) As shown in FIG. 10, the BiCuOSe.sub.0.5Te.sub.0.5 exhibits a natural super-lattice structure in which Cu.sub.2(Te,Se).sub.2 layers and Bi.sub.2O.sub.2 layers are repeated along a c-crystalline axis. Also, it can be said that Bi(Te,Se)Cu layers and O layers are repeated along the c-crystalline axis in the natural super-lattice structure.

Example 8

Bi0.9Tl0.1CuOTe

(58) In order to prepare Bi.sub.0.9Tl.sub.0.1CuOTe, 1.227 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.7114 g of Bi (Aldrich, 99.99%, <10 m), 0.6122 g of Cu (Aldrich, 99.7%, 3 m), 1.2293 g of Te (Aldrich, 99.99%, 100 mesh), and 0.22 g of Tl.sub.2O.sub.3 (Aldrich) were well mixed by using agate mortar.

(59) The mixture was then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining Bi.sub.0.9Tl.sub.0.1CuOTe powder.

(60) X-ray diffraction analysis was conducted for the sample in the same way as the example 3. As shown in FIG. 11, the material obtained in the example 8 was identified as Bi.sub.0.9Tl.sub.0.1CuOTe.

Example 9

BiCuOTe0.9Sb0.1

(61) In order to prepare BiCuOTe.sub.0.9Sb.sub.0.1, 1.4951 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 0.6705 g of Bi (Aldrich, 99.99%, <10 m), 0.6117 g of Cu (Aldrich, 99.7%, 3 m), 1.1054 g of Te (Aldrich, 99.99%, 100 mesh), and 0.1172 g of Sb (Kanto chemical, Cat. No. 01420-02) were well mixed by using agate mortar.

(62) The mixture was then heated in an evacuated silica tube at 510 C. for 15 hours, thereby obtaining BiCuOTe.sub.0.9Sb.sub.0.1 powder.

(63) X-ray diffraction analysis was conducted for the sample in the same way as the example 3. As shown in FIG. 12, the material obtained in the example 9 was identified as BiCuOTe.sub.0.9Sb.sub.0.1.

Example 10

Bi0.95Pb0.05Cu0.96OTe0.95Se0.05

(64) In order to prepare Bi.sub.0.95Pb.sub.0.05Cu.sub.0.96OTe.sub.0.95Se.sub.0.05, 3.7785 g of Bi.sub.2O.sub.3 (Aldrich, 99.9%, 100 mesh), 1.4404 g of Bi (Aldrich, 99.99%, <10 m), 1.4840 g of Cu (Aldrich, 99.7%, 3 m), 0.2520 g of Pb (Alfa aesar, 99.9%, 200 mesh), 2.9489 g of Te (Aldrich, 99.99%, 100 mesh), and 0.0960 g of Se (Alfa aesar, 99.999%, 200 mesh) were well mixed by using agate mortar.

(65) The mixture was then heated in an evacuated silica tube at 500 C. for 12 hours, thereby obtaining Bi.sub.0.95Pb.sub.0.05Cu.sub.0.96OTe.sub.0.95Se.sub.0.05 powder.

(66) X-ray diffraction analysis was conducted for the sample in the same way as the example 3, and the material obtained in the example 10 was identified as Bi.sub.0.95Pb.sub.0.05Cu.sub.0.96OTe.sub.0.95Se.sub.0.05.

(67) Evaluation of Thermoelectric Conversion Performance

(68) Powder samples obtained in Examples 1, 3 to 6, 8 and 10 were shaped into cylinders with a diameter of 4 mm and a length of 15 mm (for electrical conductivity and Seebeck coefficient measurements), and disks having a diameter of 10 mm and a thickness of 1 mm (for thermal conductivity measurements) by using CIP at the pressure of 200 MPa. Subsequently, the resultant disks and cylinders were heated in an evacuated silica tube at 510 C. for 10 hours (for 12 hours for Example 10).

(69) For the sintered cylinders, electric conductivity and Seebeck coefficient were measured by using a ZEM-2 (Ulvac-Rico, Inc.) The measurement results are shown in FIGS. 13 to 19. For example, at 346 K thermal conductivities of BiCuOTe and Bi.sub.0.98Pb.sub.0.02CuOTe were measured as 0.25 W/m/K and 0.35 W/m/K, respectively, which are significantly lower than those of Bi.sub.2Te.sub.3 (1.9 W/m/K, T. M. Tritt, M. A. Subramanian, MRS Bulletin 31 (2006) 188-194) and Co.sub.4Sb.sub.12:In.sub.0.2 (2 W/m/K, T. He, J. Chen, D. Rosenfeld, M. A. Subramanian, Chem. Mater. 18 (2006) 759-762) which are representative thermoelectric conversion materials.

(70) Meanwhile, for the sintered disks, thermal conductivity was measured by using TC-9000 (Ulvac-Rico, Inc) (using a LFA457 (Netzsch) for Example 10). The measurement results are shown in FIGS. 13 to 19.

(71) ZT value of each sample was calculated using the measured values. The calculated results are shown in FIGS. 13 to 19.