THERMOELECTRIC ARTICLE AND COMPOSITE MATERIAL FOR A THERMOELECTRIC CONVERSION DEVICE AND PROCESS FOR PRODUCING A THERMOELECTRIC ARTICLE
20190207073 · 2019-07-04
Assignee
Inventors
Cpc classification
C22F1/00
CHEMISTRY; METALLURGY
International classification
Abstract
A thermoelectric article and process for producing a thermoelectric article for a thermoelectric conversion device is provided. The thermoelectric article has an overall composition consisting essentially of 6 atom %Ti27 atom %, 6 atom %Zr27 atom %, 0 atom %Hf1.7 atom %, where 28 atom %(Ti+Zr+Hf)38 atom %;
28 atom %Sn38 atom %, 0 atom %Sb3 atom %, where 28 atom %(Sn+Sb)38 atom %; 0 atom %A7 atom %, 0 atom %B7 atom %, where A is Sc, Y and/or La, B is V, Nb and/or Ta and 0.15 atom %A+B7 atom %; the rest being Ni and up to 5 atom % impurities.
Claims
1. A thermoelectric article for a thermoelectric conversion device having an overall composition consisting essentially of 6 atom %Ti27 atom %, 6 atom %Zr27 atom %, 0 atom %Hf1.7 atom %, where 28 atom %(Ti+Zr+Hf)38 atom %; 28 atom %Sn38 atom %, 0 atom %Sb3 atom %, where 28 atom %(Sn+Sb)38 atom %; 0 atom %A7 atom %, 0 atom %B7 atom %, where A is one or more of the elements selected from the group consisting of Sc, Y and La, B is one or more of the elements selected from the group consisting of V, Nb and Ta and 0.15 atom %A+B7 atom %; the rest being Ni and up to 5 atom % impurities.
2. A thermoelectric article according to claim 1, wherein the thermoelectric article comprises at least one phase with a half-Heusler structure.
3. A thermoelectric article according to claim 2, wherein the phase with the half-Heusler structure comprises less than 0.2 atom % of one or more of the elements A and B.
4. A thermoelectric article according to claim 2, wherein the composition of the phases with the half-Heusler structure is defined by the chemical formula Ti.sub.aZr.sub.1-aNiSn.sub.1-bSb.sub.b, where 0a1 and 0b0.1.
5. A thermoelectric article according to claim 1, wherein the thermoelectric article comprises one or more A-rich phases without a half-Heusler structure and one or more B-rich phases without a half-Heusler structure.
6. A thermoelectric article according to claim 1, wherein the overall composition is A.sub.xB.sub.yTi.sub.a1Zr.sub.a2Hf.sub.a3NiSn.sub.cSb.sub.b, where 0x0.2, 0y0.2, 0.005(x+y)0.2, 0.2a10.8, 0.2a20.8, 0a30.05, 0.9(a1+a2+a3)1.1, 0b0.1 and 0.9(b+c)1.1.
7. A thermoelectric article according to claim 6, wherein x=y.
8. A thermoelectric article according to claim 1, the thermoelectric article having a maximum thermoelectric figure of merit ZT.sub.max of 0.8.
9. A thermoelectric article according to claim 1, the thermoelectric article having a thermoelectric figure of merit ZT.sub.max of ZT.sub.max0.8, where 400 C.T.sub.max700 C.
10. A thermoelectric article according to claim 1, the thermoelectric article having a Seebeck coefficient S where 350S80 (V/K).
11. A thermoelectric article according to claim 1, the thermoelectric article having a maximum power factor PF.sub.max of >3.5 (mW m.sup.1 K.sup.2).
12. A composite material for a thermoelectric conversion device comprising: a matrix with at least one phase with a Ni-based half-Heusler structure, being at least one of the elements in a group consisting of Ti, Zr and Hf and being at least one of the elements in the group consisting of Sn and Sb, where the proportion of Hf is less than 1.7 atom %, inclusions from an A-rich phase, A being one or more of the elements selected from the group consisting of Sc, Y and La, and inclusions from a B-rich phase, B being one or more of the elements selected from the group consisting of V, Nb and Ta, and a maximum thermoelectric figure of merit ZT.sub.max of 0.8.
13. A composite material according to claim 12, wherein the composition of the phases with the half-Heusler structure is defined by the chemical formula Ti.sub.aZr.sub.1-aNiSn.sub.1-bSb.sub.b, where 0a1 and 0b0.1.
14. A composite material according to claim 12, wherein the matrix comprises less than 0.2 atom % of one or more of the elements A and B.
15. A composite material according to claim 12, wherein the inclusions from an A-rich phase and the inclusions from a B-rich phase do not have a half-Heusler structure.
16. A composite material according to claim 12, wherein the composite material comprises up to 10 vol % of the A-rich phase and the B-rich phase.
17. A composite material according to claim 12, the composite material having an overall composition consisting essentially of 6 atom %Ti27 atom %, 6 atom %Zr27 atom %, 0 atom %Hf1.7 atom %, where 28 atom %(Ti+Zr+Hf)38 atom %; 28 atom %Sn38 atom %, 0 atom %Sb3 atom %, where 28 atom %(Sn+Sb)38 atom %; 0 atom %A7 atom %, 0 atom %B7 atom %, where A is one or more of the elements chosen from the group consisting of Sc, Y and La, B is one or more of the elements selected from the group consisting of V, Nb and Ta and 0.15 atom %A+B7 atom %; the rest being Ni and up to 5 atom % impurities.
18. A composite material according to claim 12, the composite material having a maximum thermoelectric figure of merit ZT.sub.max where ZT.sub.max0.8 and 400 C.T.sub.max700 C.
19. A composite material according to claim 12, the composite material having a maximum power factor PF.sub.max of >3.5 (mW m.sup.1 K.sup.2).
20. A thermoelectric module having at least one thermoelectric element made of a composite material according to claim 12.
21. A process for producing a thermoelectric article for a thermoelectric conversion device, the process comprising: providing a starting material consisting essentially of 6 atom %Ti27 atom %, 6 atom %Zr27 atom %, 0 atom %Hf1.7 atom %, where 28 atom %(Ti+Zr+Hf)38 atom %; 28 atom %Sn38 atom %, 0 atom %Sb3 atom %, where 28 atom %(Sn+Sb)38 atom %; 0 atom %A7 atom %, 0 atom %B7 atom %, where A is one or more of the elements chosen from the group consisting of Sc, Y and La, B is one or more of the elements selected from the group consisting of V, Nb and Ta and 0.15 atom %A+B7 atom %; the rest being Ni and up to 5 atom % impurities, melting and subsequently hardening the starting material to form at least one block, homogenising the block at a temperature of 900 C. to 1200 C. for a length of time t, where 0.5 ht100 h, to form a homogenised block, crushing the homogenised block, grinding the reduced block, a powder thereby being formed, cold pressing the powder, a green body thereby being formed, sintering the green body at a maximum pressure of 1 MPa at a temperature of 1000 C. to 1500 C. for 0.5 h to 24 h, thereby producing a thermoelectric article.
22. A process according to claim 21, further comprising casting the molten starting material into a block.
23. A process according to claim 21, wherein the block is reduced to small pieces by means of a jaw crusher.
24. A process according to claim 21, the crushing is performed by use of a disc mill or a roller mill.
25. A process according to claim 21, wherein the block is reduced to a coarse powder, the coarse powder then being ground to a fine powder in a further grinding process and the fine powder being cold pressed.
26. A process according to claim 25, wherein the further grinding process is carried out by means of a planetary ball mill or a jet mill.
27. A process according to claim 21, wherein the starting material is melted by vacuum induction melting.
28. A process according to claim 21, wherein the block is homogenised in argon or in a vacuum.
29. A process according to claim 21, wherein the block is homogenised at a temperature of 1050 C. to 1180 C. for a length of time t, where 16 ht36 h.
30. A process for producing a thermoelectric article comprising the following: providing a first powder comprising essentially 6 atom %Ti27 atom %, 6 atom %Zr27 atom %, 0 atom %Hf1.7 atom %, where 28 atom %(Ti+Zr+Hf)38 atom %; 28 atom %Sn38 atom %, 0 atom %Sb3 atom %, 28 atom %(Sn+Sb)38 atom %; the rest being Ni and up to 5 atom % impurities, the proportion of elements from groups A and B being less than 0.2 atom %, providing a second powder comprising 0 atom %A7 atom % and/or 0 atom %B7 atom %, where A is one or more of the elements chosen from the group consisting of Sc, Y and La, B is one or more of the elements selected from the group consisting of V, Nb and Ta and 0.15 atom %A+B7 atom %, mixing the first powder and the second powder, thereby producing a starting powder, cold pressing the starting powder, thereby forming a green body, sintering the green body at a maximum pressure of 1 MPa at a temperature of 1000 C. to 1500 C. for 0.5 h to 24 h, thereby producing a thermoelectric article.
31. A process according to claim 30, wherein the green body is sintered in a protective gas or a vacuum.
32. A process according to claim 30, wherein the thermoelectric article is processed into a plurality of working components by means of sawing and/or grinding processes.
33. A process according to claim 30, the second powder further comprising 6 atom %Ti27 atom %, 6 atom %Zr27 atom %, 0 atom %Hf1.7 atom %, where 28 atom %(Ti+Zr+Hf)38 atom %; 28 atom %Sn38 atom %, 0 atom %Sb3 atom %, where 28 atom %(Sn+Sb)38 atom %; the rest being Ni and up to 5 atom % impurities.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] The invention is explained in greater detail below using the drawings and examples.
[0052]
[0053]
[0054]
[0055]
[0056]
[0057]
[0058]
[0059]
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0060] A thermoelectric article having an overall composition consisting essentially of 6 atom %Ti27 atom %, 6 atom %Zr27 atom %, where 28 atom %(Ti+Zr)38 atom %; 0 atom %Hf1.7 atom %, where one or both of the elements Ti and Zr of the half-Heusler phase can be partially replaced by Hf such that 28 atom %(Ti+Zr+Hf)38 atom %, where the proportion of Hf in the sum (Ti+Zr+Hf)5 atom %; 28 atom %Sn38 atom %, 0 atom %Sb3 atom %, where 28 atom %(Sn+Sb)38 atom %; 0 atom %A7 atom %, 0 atom %B7 atom %, where A is one or more of the elements selected from the group consisting of Sc, Y and La, B is one or more of the elements selected from the group consisting of V, Nb and Ta and 0.15 atom %A+B7; the rest being Ni and up to 5 atom % of impurities. The thermoelectric article has a sintered, multi-phase composite structure with a matrix consisting of at least one phase with a half-Heusler structure with less than 0.2 atom % of the elements A and B and inclusions or precipitates of A-rich and/or B-rich phases embedded in the matrix.
[0061] In the examples set out above, the overall composition comprises both elements Ti.sub.cZr.sub.1-c in a ratio of 0.2c0.8 with only a small proportion of hafnium. The composition regions of the lattice site examined in relation to A and B substitution in this work are shown as a shaded area in
[0062] A series of test was carried out to examine the influence of substitution with A and B atoms in the system A.sub.xB.sub.y(Ti.sub.cZr.sub.1-c).sub.1-x-yNiSn in which x and y varied between 0.005x,y0.13. The target range for the composition on the lattice site was set with c between 0.2c0.8. The elements Ti and Zr were partially replaced by small amounts of Hf, the proportion of Hf in Ti+Zr+Hf being less than 5 atom %.
[0063] It was established in the tests that, surprisingly, no pure half-Heusler compounds are obtained. The atoms from the groups A and B could not be detected detached in the half-Heusler phase, the detection limit in the energy-dispersive X-ray spectroscopy method of analysis chosen being approx. 0.2%. Instead A- and B-rich foreign phases formed even at small quantities of substitution atoms (x, y=0.005).
[0064] It was similarly surprising that good thermoelectric properties with high ZT values were measured at these half-Heusler compounds with integrated A- and B-rich phases. It is not therefore necessary to avoid the occurrence of foreign phases in order to obtain good thermoelectric materials.
[0065] In the half-Heusler compounds Ti.sub.cZr.sub.1-cNiSn described here with 0.2c0.8, the solubility of the A and B atoms appears to be significantly reduced, so resulting in the foreign phases observed. This lack of solubility in the half-Heusler phase is surprising. It is also surprising that these foreign phases have an advantageous influence on thermoelectric properties.
Example 1
[0066] Materials with the composition shown in Table 1 were produced. This was achieved by melting the materials in the composition given by means of vacuum induction melting. Due to the content of 2.7 mass % Hf as an accompanying element in the Zr used, 0.4 atom % of the Zr and Ti in the molten materials were replaced by Hf. The cast block was further processed by first homogenising it at 1000 C. in argon as a protective gas for 24 hours and then grinding it into a fine powder with a median particle size of less than 10 m. The powder was then pressed into green bodies at a pressure of 2 t/cm2 in a tool press and finally sintered at 1100 C. to 1300 C. for 4 hours in a vacuum to form a dense body.
TABLE-US-00001 TABLE 1 Composition of materials according to Example 1 and their Seebeck coefficients at room temperature Composition in atom % S (V/K) @ RT Example 1.1 4.2% La4.2% Ta16.7% 38 Ti8.3% Zr33.3% Sn, rest Ni Example 1.2 4.2% Y4.2% Ta16.7% 56 Ti8.3% Zr33.3% Sn, rest Ni Example 1.3 4.2% La4.2% Nb16.7% 22 Ti8.3% Zr33.3% Sn, rest Ni Example 1.4 4.2% Y4.2% Nb16.7% 41 Ti8.3% Zr33.3% Sn, rest Ni
[0067] The microstructure of materials produced in this way was examined using scanning electron microscopy (SEM).
[0068] Rods with dimensions of 3 mm3 mm13 mm were sawed from the materials. The Seebeck coefficients of these samples were determined at room temperature and are also listed in Table 1. The maximum Seebeck coefficient was 56 V/K for Example 1.2. The Seebeck coefficients of the materials from Example 1 were therefore too low to be useful for practical thermoelectric energy conversion. However, the proportion of A- and B-rich auxiliary phases in Example 1 is very high. The series of tests in Example 2 below was therefore devised to examine the influence of a lower proportion of these foreign phases on thermoelectric properties.
Example 2
[0069] First, as a comparative example, a powder made of a material without elements from groups A and B was produced as in Example 1. The composition corresponds to a half-Heusler phase and is given in Table 2. Due to the content of 2.7 mass % Hf as an accompanying element in the Zr used a total of 0.7 atom % of the Zr and Ti is replaced by Hf. Further materials, their compositions also given in Table 2, were produced by mixing the powder from Example 1 with the powder from Example 2.1 in various ratios and by the subsequent pressing and sintering of the powder mixtures as in Example 1. The materials from Example 2 contain smaller proportions of elements from groups A and B than those from Example 1.
TABLE-US-00002 TABLE 2 Composition of materials according to Example 2 Composition in atom % Comp. example 2.1 16.7% Ti16.7% Zr33.3% Sn, rest Ni Example 2.2 0.17% La0.17% Ta16.7% Ti16.3% Zr33.3% Sn, rest Ni Example 2.3 0.5% La0.5% Ta16.7% Ti15.7% Zr33.3% Sn, rest Ni Example 2.4 0.8% La0.8% Ta16.7% Ti15.0% Zr33.3% Sn, rest Ni Example 2.5 1.7% La1.7% Ta16.7% Ti13.3% Zr33.3% Sn, rest Ni Example 2.6 0.5% Y0.5% Ta16.7% Ti15.7% Zr33.3% Sn, rest Ni Example 2.7 0.8% Y0.8% Ta16.7% Ti15.0% Zr33.3% Sn, rest Ni Example 2.8 0.5% La0.5% Ta16.7% Ti15.7% Zr33.3% Sn, rest Ni Example 2.9 0.8% La0.8% Nb16.7% Ti15.0% Zr33.3% Sn, rest Ni Example 2.10 0.5% Y0.5% Nb16.7% Ti15.7% Zr33.3% Sn, rest Ni Example 2.11 0.8% Y0.8% Nb16.7% Ti15.0% Zr33.3% Sn, rest Ni
[0070] The microstructure of the materials was examined by means of SEM. The microstructure of the material from Example 2.4 is shown in
[0071] The EDX analysis of the half-Heusler phases in
[0072] Rods with dimensions of 3 mm3 mm13 mm were sawed from the materials. The Seebeck coefficients and electrical conductivity of these samples were measured. The results and the power factors calculated from them are listed in Table 3. As the table shows, the materials from Example 2 have a clearly higher Seebeck coefficient than the materials from Example 1. Furthermore, in all of examples 2.2 to 2.11, which possess a proportion of A- and B-rich foreign phases, the power factor is clearly higher than in the comparative Example 2.1, which consists of a half-Heusler phase without A- and B-rich foreign phases. Example 2 therefore demonstrates, contrary to expectations, that the presence of A- and B-rich foreign phases improves rather than diminishes thermoelectric properties.
TABLE-US-00003 TABLE 3 Thermoelectric properties of materials from Example 2 at room temperature and 400 C. RT 400 C. S PF S PF (V/ (S/ (mWm.sup.1 (V/ (S/ (mWm.sup.1 K) cm) K.sup.2) K) cm) K.sup.2) Comp. 248 198 1.2 241 478 2.8 example 2.1 Example 2.2 199 482 1.9 226 643 3.3 Example 2.3 144 1061 2.2 203 890 3.7 Example 2.4 123 1474 2.2 185 1140 3.9 Example 2.5 85 2637 1.9 141 1866 3.7 Example 2.6 143 1142 2.3 200 967 3.9 Example 2.7 137 1211 2.3 196 1020 3.9 Example 2.8 131 1196 2.1 185 1035 3.6 Example 2.9 97 1954 1.8 154 1466 3.5 Example 2.10 138 1111 2.1 192 976 3.6 Example 2.11 112 1544 1.9 169 1203 3.4
Example 3
[0073] In Example 3 the effect of A- and B-rich foreign phases for half-Heusler compounds are examined with a further composition range of the lattice site. To this end, A- and B-free half-Heusler compounds with the composition 10.0% Ti23.3% Zr33.3% Snrest Ni (Ti.sub.0.4Zr.sub.0.6NiSn) and 23.3% Ti10.0% Zr33.3% Snrest Ni (Ti.sub.0.7Zr.sub.0.3NiSn) were melted as in Example 1. Due to the content of 2.7 mass % Hf as an accompanying element in the Zr used, in the compounds a total of 1%, 0.8% or 0.4% of the Zr and Ti are replaced by Hf. As in Example 2, the compounds were processed into a powder and then mixed in various ratios with the powders of the materials from Example 1. These were then made into dense test pieces with the compositions listed in Table 4 by means of sintering.
TABLE-US-00004 TABLE 4 Composition of materials according to Example 3 Composition in atom % Example 3.1 0.3% La0.3% Ta10.5% Ti22.1% Zr33.3% Sn, rest Ni Example 3.2 0.8% La0.8% Ta11.3% Ti20.3% Zr33.3% Sn, rest Ni Example 3.3 0.3% La0.3% Ta13.6% Ti19.1% Zr33.3% Sn, rest Ni Example 3.4 0.8% La0.8% Ta14.0% Ti17.7% Zr33.3% Sn, rest Ni Example 3.5 0.8% Y0.8% Ta11.3% Ti20.3% Zr33.3% Sn, rest Ni Example 3.6 0.8% Y0.8% Ta22.0% Ti10.0% Zr33.3% Sn, rest Ni
[0074] Rods with dimensions of 3 mm3 mm13 mm were sawed from the materials to measure Seebeck coefficients and electrical conductivity. Samples with dimensions of 10 mm10 mm1 mm were also produced to measure heat conductivity using the laser flash method. The temperature-dependent thermoelectric properties measured for the materials in this way are shown in
[0075]
[0076] All the materials from Example 3 present a high Seebeck coefficient. Alongside the electrical conductivity measured, there are also high power factors comparable with the materials from Example 2. Example 3 therefore shows that the A- and B-rich foreign phases also have an advantageous effect on thermoelectric properties in the extended composition range of the lattice site.
[0077] This is confirmed by the measurement of heat conductivity. As shown in
Example 4
[0078] The materials used in the preceding examples each contain elements from both groups A and B together. No solubility of these elements was observed in the half-Heusler phase. In Example 4 it is demonstrated that when only one element from one of groups A and B are added there is no solubility of this element in the half-Heusler phase. To ascertain this the compositions listed in Table 5 were melted using vacuum induction melting and processed as described in Example 1.
TABLE-US-00005 TABLE 5 Composition of materials according to Example 4 Composition in atom % Example 4.1 0.8% La16.7% Ti15.8% Zr33.3% Sn - rest Ni Example 4.2 0.8% Ta16.7% Ti15.8% Zr33.3% Sn- rest Ni
[0079] The materials produced in this way were analysed using SEM. The microstructures of the materials from Example 4 are shown in
Example 5
[0080] In Example 5 the thermoelectric properties of materials with Ti-rich auxiliary phases are compared with the thermoelectric properties of conventional half-Heusler compounds in which the tin lattice site has been antimony-doped. To this end the compositions listed in Table 6 were melted by vacuum induction melting and processed as described in Example 1. In addition to the processing described in Example 1, the materials were annealed for 48 hours at 930 C. in a protective gas (argon) prior to characterisation.
TABLE-US-00006 TABLE 6 Composition of materials according to Example 5 Composition in atom % Example 5.1 0.3% Ta16.7% Ti16.3% Zr33.3% Sn - rest Ni Example 5.2 0.8% Ta16.7% Ti15.8% Zr33.3% Sn- rest Ni Comp. example 5.3 16.7% Ti16.7% Zr33.0% Sn0.3% Sb - rest Ni Comp. example 5.4 16.7% Ti16.7% Zr32.7% Sn0.7% Sb - rest Ni
[0081] Rods with dimensions of 2.5 mm2.5 mm13 mm were sawed from the materials to measure Seebeck coefficients and electrical conductivity, and samples with dimensions of 10 mm10 mm1 mm were taken to measure heat conductivity using the laser flash method. The temperature-dependent thermoelectric properties measured for the materials in this way are shown in
[0082]
[0083] A comparison of the data shows that the materials from Examples 5.1 and 5.2 cover similar ranges for Seebeck coefficient and electrical conductivity as the materials in the comparative examples 5.3 and 5.4. The power factors and ZT values, however, are clearly higher in the materials from Examples 5.1 and 5.2. These materials, which correspond to this invention and contain Ta-rich auxiliary phases, reach maximum ZT values of between 0.9ZT.sub.max1.0 in the temperature range 500 C. to 600 C. In the same temperature range, by contrast, materials from conventionally doped half-Heusler compounds without Ta-rich foreign phases reach only maximum ZT values of less than 0.9.
Example 6
[0084] In Example 6 the thermoelectric properties of materials which possess A-rich and/or B-rich auxiliary phases in combination with an antimony-doped half-Heusler compound are examined. To this end, the compositions listed in Table 7 were melted, processed in the manner described in Example 1 and then annealed for 48 hours at 930 C. in a protective gas (argon).
TABLE-US-00007 TABLE 7 Composition of materials according to Example 6 Composition in atom % Example 6.1 0.4% Ta16.7% Ti16.3% Zr33.2% Sn0.2% Sb - rest Ni Example 6.2 0.4% Ta16.7% Ti16.3% Zr33.0% Sn0.3% Sb - rest Ni Example 6.3 0.4% La0.4% Ta16.7% Ti15.8% Zr33.0% Sn0.3% Sb - rest Ni Example 6.4 0.6% Ta16.7% Ti15.8% Zr1.5% Hf33.2% Sn0.2% Sb - rest Ni
[0085] The measurement samples prepared from the materials for thermoelectric characterisation were produced as described in Example 5. The thermoelectric properties measured are shown in
[0086]
[0087] The materials from Example 6 all achieve very good thermoelectric properties with high power factors and a maximum ZT value in a temperature range of between 500 C. and 600 C. of 0.9ZT.sub.max1.0. In particular, the power factors and ZT values achieved are higher than in the comparative Examples 5.3 and 5.4, which represent antimony-doped half-Heusler compounds without A- and/or B-rich auxiliary phases.
[0088] It is therefore possible with this invention to produce higher-performance, low-Hf, thermoelectric materials based on NiSn half-Heusler compounds. These materials have a multi-phase composite structure in which inclusions from A-rich and/or B phases are embedded in a matrix with one or more phases with a half-Heusler structure, the phases with the half-Heusler structure comprising at least 6 atom % Ti and 6 atom % Zr.
Key to FIG. 4
[0089] Seebeck coefficient (V/K)
Temperature ( C.)
Example 3.1 etc.
[0090] Electrical conductivity (S/cm)
Temperature ( C.)
Example 3.1 etc.
[0091] Power factor (mWm.sup.1K.sup.2)
Temperature ( C.)
Example 3.1 etc.
[0092] Heat conductivity (mWm.sup.1K.sup.1)
Temperature ( C.)
Example 3.1 etc.
ZT
Temperature ( C.)
Example 3.1 etc.
Key to FIG. 7
[0093] Seebeck coefficient (V/K)
Temperature ( C.)
Example 5.1 etc.
[0094] Comp. example 5.3 etc.
Electrical conductivity (S/cm)
Temperature ( C.)
Example 5.1 etc.
[0095] Comp. example 5.3 etc.
Power factor (mWm.sup.1K.sup.2)
Temperature ( C.)
Example 3.1 etc.
[0096] Comp. example 5.3 etc.
Heat conductivity (mWm.sup.1K.sup.1)
Temperature ( C.)
Example 3.1 etc.
[0097] Comp. example 5.3 etc.
ZT
Temperature ( C.)
Example 3.1 etc.
[0098] Comp. example 5.3 etc.
Key to FIG. 8
[0099] Seebeck coefficient (V/K)
Temperature ( C.)
Example 6.1 etc.
[0100] Electrical conductivity (S/cm)
Temperature ( C.)
Example 6.1 etc.
[0101] Power factor (mWm.sup.1K.sup.2)
Temperature ( C.)
Example 6.1 etc.
[0102] Heat conductivity (mWm.sup.1K.sup.1)
Temperature ( C.)
Example 6.1 etc.
ZT
Temperature ( C.)
Example 6.1 etc.