Chalcogen-containing compound, its preparation method and thermoelectric element comprising the same

Abstract

A chalcogen-containing compound of the following Chemical Formula 1, which may have decreased thermal conductivity and improved power factor in the low temperature region, and thus exhibit an excellent thermoelectric figure of merit, a method for preparing the same, and a thermoelectric element including the same:
V.sub.1Sn.sub.a−xIn.sub.xSb.sub.2Te.sub.a+3  [Chemical Formula 1]
wherein V, a and x are as defined in the specification.

Claims

1. A chalcogen-containing compound represented by the following Chemical Formula 1:
V.sub.1Sn.sub.a−xIn.sub.xSb.sub.2Te.sub.a+3  [Chemical Formula 1] wherein, V is a vacancy, 14≤a≤16, and 0<x≤0.5.

2. The chalcogen-containing compound according to claim 1, wherein 0.01≤x≤0.2.

3. The chalcogen-containing compound according to claim 1, wherein the chalcogen-containing compound has a face-centered cubic lattice structure.

4. The chalcogen-containing compound according to claim 3, wherein the V is a vacant site excluding sites filled with Sn, Sb, and Te in the face-centered cubic lattice structure, and the In is substituted for a part of Sn.

5. The chalcogen-containing compound according to claim 3, wherein the Te is filled in anionic sites of the face-centered cubic lattice structure, the Sn and Sb are filled in cationic sites of the face-centered cubic lattice structure, the In is substituted for a part of Sn, and the V is a vacant site of remaining cationic sites excluding sites filled with Sn, Sb, and In.

6. The chalcogen-containing compound according to claim 3, wherein the V, Sn, Sb, and In are randomly distributed at the site of (x, y, z)=(0, 0, 0), and Te is distributed at the site of (x, y, z)=(0.5, 0.5, 0.5).

7. The chalcogen-containing compound according to claim 1, wherein a is 14, and the chalcogen-containing compound has a face-centered cubic lattice structure, a lattice constant of 6.2850 Å to 6.2861 Å, and a weighted pattern R (Rwp) of 5.900 to 5.990.

8. The chalcogen-containing compound according to claim 1, wherein a is 16, and the chalcogen-containing compound has a face-centered cubic lattice structure, a lattice constant of 6.2880 Å to 6.2900 Å, and a weighted pattern R (Rwp) of 4.900 to 5.100.

9. The chalcogen-containing compound according to claim 1, wherein the chalcogen-containing compound is selected from the group consisting of V.sub.1Sn.sub.13.9In.sub.0.1Sb.sub.2Te.sub.17, V.sub.1Sn.sub.13.8In.sub.0.2Sb.sub.2Te.sub.17, V.sub.1Sn.sub.15.9In.sub.0.1Sb.sub.2Te.sub.19, and V.sub.1Sn.sub.15.8In.sub.0.2Sb.sub.2Te.sub.19.

10. A method for preparing the chalcogen-containing compound of claim 1, comprising the steps of: mixing respective raw materials of Sn, Sb, Te, and In in amounts such that the mole ratio of Sn:Sb:Te:In is (a−x):2:(a+3):x, and subjecting the resultant mixture to a melting reaction; heat-treating the resultant product obtained through the melting reaction; pulverizing the resultant product obtained through the heat treatment; and sintering the pulverized product.

11. The method for preparing the chalcogen-containing compound according to claim 10, wherein the melting reaction is conducted at a temperature of 700° C. to 900° C.

12. The method for preparing the chalcogen-containing compound according to claim 10, wherein the heat treatment is conducted at a temperature of 550° C. to 640° C.

13. The method for preparing the chalcogen-containing compound according to claim 10, further comprising a step of cooling the resultant product of the heat treatment step to form an ingot, between the heat treatment step and the pulverization step.

14. The method for preparing the chalcogen-containing compound according to claim 10, wherein the sintering is conducted by a spark plasma sintering method, at a temperature of 550° C. to 640° C. and a pressure of 10 MPa to 100 MPa.

15. A thermoelectric element comprising the chalcogen-containing compound according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a mimetic diagram showing a face-centered cubic lattice structure.

(2) FIG. 2 is a mimetic diagram showing the lattice structure of the chalcogen-containing compound according to one embodiment of the present invention.

(3) FIG. 3 shows X-ray diffraction (XRD) analysis results of chalcogen compound powders prepared in Examples 1 to 4 and Comparative Examples 1 and 2.

(4) FIG. 4 shows the X-ray diffraction analysis results of chalcogen compound powders prepared in Comparative Examples 3 to 7.

(5) FIG. 5 is a graph showing the results of measuring electrical conductivities of the chalcogen compounds of Examples 1 to 4 and Comparative Examples 1 to 5 according to temperature.

(6) FIG. 6 is a graph showing the results of measuring Seebeck coefficients of the chalcogen compounds of Examples 1 to 4 and Comparative Examples 1 to 5 according to temperature.

(7) FIG. 7 is a graph showing the results of measuring power factors of the chalcogen compounds of Examples 1 to 4 and Comparative Examples 1 to 5 according to temperature.

(8) FIG. 8 is a graph showing the results of measuring total thermal conductivities of the chalcogen compounds of Examples 1 to 4 and Comparative Examples 1 to 5 according to temperature.

(9) FIG. 9 is a graph showing the thermoelectric figures of merit of the chalcogen compounds of Examples 1 to 4 and Comparative Examples 1 to 5 according to temperature.

(10) FIG. 10 is a graph showing the average power factors according to an indium substitution amount in the chalcogen-containing compounds of Examples 1 and 2 and Comparative Example 1 (temperature region: 100˜500° C.).

(11) FIG. 11 is a graph showing the average values of the thermoelectric figures of merit according to an indium substitution amount in the chalcogen-containing compounds of Examples 1 and 2 and Comparative Example 1 (temperature region: 100˜500° C.).

(12) FIG. 12 is a graph showing the average power factors according to an indium substitution amount in the chalcogen-containing compounds of Examples 3 and 4 and Comparative Example 2 (temperature region: 100˜500° C.).

(13) FIG. 13 is a graph showing the average values of the thermoelectric figures of merit according to an indium substitution amount in the chalcogen-containing compounds of Examples 3 and 4 and Comparative Example 2 (temperature region: 100˜500° C.).

BEST MODE FOR CARRYING OUT THE INVENTION

(14) The present invention will be explained in more detail in the following examples. However, these examples are presented only as the illustrations of the present invention, and the scope of the present invention is not limited thereby.

Comparative Example 1: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.14.Sb.SUB.2.Te.SUB.17

(15) High purity raw materials Sn shot, Sb shot, and Te shot were weighed in a glovebox at a mole ratio of 14:2:17, put in a carbon crucible, and then charged into a quartz tube. The inside of the quartz tube was vacuumized and sealed. Subsequently, the raw materials were maintained at a constant temperature in an electric furnace at 750 for hours, and then slowly cooled to room temperature. Thereafter, they were heat treated at 640 for 48 hours, and the quartz tube in which the reaction was progressed was cooled with water to obtain an ingot. The ingot was finely pulverized to powder with a particle diameter of 75 μm or less, and sintered by spark plasma sintering (SPS) at a temperature of 600 and a pressure of 50 MPa for 8 minutes, thus preparing a chalcogen-containing compound.

Comparative Example 2: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.16.Sb.SUB.2.Te.SUB.19

(16) High purity raw materials Sn shot, Sb shot, and Te shot were weighed in a glovebox at a mole ratio of 16:2:19, put in a carbon crucible, and then charged into a quartz tube. The inside of the quartz tube was vacuumized and sealed. The raw materials were maintained at a constant temperature in an electric furnace at 750 for 12 hours, and then slowly cooled to room temperature. Thereafter, they were heat treated at 640° C. for 48 hours, and the quartz tube in which a reaction was progressed was cooled with water to obtain an ingot. The ingot was finely pulverized to powder with a particle diameter of 75 μm or less, and sintered by spark plasma sintering (SPS) at a temperature of 600° C. and a pressure of 50 MPa for 8 minutes, thus preparing a chalcogen-containing compound.

Comparative Example 3: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.13.2.In.SUB.0.8.Sb.SUB.2.Te.SUB.17

(17) High purity raw materials Sn shot, In powder, Sb shot, and Te shot were weighed in a glovebox at a mole ratio of 13.2:0.8:2:17, put in a carbon crucible, and then charged into a quartz tube. The inside of the quartz tube was vacuumized and sealed. Subsequently, the raw materials were maintained at a constant temperature in an electric furnace at 750 for 12 hours, and then slowly cooled to room temperature. Thereafter, they were heat treated at 640° C. for 48 hours, and the quartz tube in which a reaction was progressed was cooled with water to obtain an ingot. The ingot was finely pulverized to powder with a particle diameter of 75 μm or less, and sintered by spark plasma sintering (SPS) at a temperature of 600° C. and a pressure of 50 MPa for 8 minutes, thus preparing a chalcogen-containing compound.

Comparative Example 4: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.10.In.SUB.2.Te.SUB.13

(18) High purity raw materials Sn shot, In powder, and Te shot were weighed in a glovebox at a mole ratio of 10:2:13, put in a carbon crucible, and then charged into a quartz tube. The inside of the quartz tube was vacuumized and sealed. Subsequently, the raw materials were maintained at a constant temperature in an electric furnace at 750 for hours, and then slowly cooled to room temperature. Thereafter, they were heat treated at 640 for 48 hours, and the quartz tube in which a reaction was progressed was cooled with water to obtain an ingot. The ingot was finely pulverized to powder with a particle diameter of 75 μm or less, and sintered by spark plasma sintering (SPS) at a temperature of 600° C. and a pressure of 50 MPa for 8 minutes, thus preparing a chalcogen-containing compound.

Comparative Example 5: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.10.Sb.SUB.2.Te.SUB.13

(19) High purity raw materials Sn shot, Sb shot, and Te shot were weighed in a glovebox at a mole ratio of 10:2:13, put in a carbon crucible, and then charged into a quartz tube. The inside of the quartz tube was vacuumized and sealed. Subsequently, the raw materials were maintained at a constant temperature in an electric furnace at 750° C. for 12 hours, and then slowly cooled to room temperature. Thereafter, they were heat treated at 640° C. for 48 hours, and the quartz tube in which a reaction was progressed was cooled with water to obtain an ingot. The ingot was finely pulverized to powder with a particle diameter of 75 μm or less, and sintered by spark plasma sintering (SPS) at a temperature of 600° C. and a pressure of 50 MPa for 8 minutes, thus preparing a chalcogen-containing compound.

Comparative Example 6: Preparation of a Chalcogen-Containing Compound of V.SUB.0.7.Sn.SUB.13.9.In.SUB.0.4.Sb.SUB.2.Te.SUB.17

(20) High purity raw materials Sn shot, In powder, Sb shot, and Te shot were weighed in a glovebox at a mole ratio of 13.9:0.4:2:17, put in a carbon crucible, and then charged into a quartz tube. The inside of the quartz tube was vacuumized and sealed. Subsequently, the raw materials were maintained at a constant temperature in an electric furnace at 750 for 12 hours, and then slowly cooled to room temperature. Thereafter, they were heat treated at 640° C. for 48 hours, and the quartz tube in which a reaction was progressed was cooled with water to obtain an ingot. The ingot was finely pulverized to powder with a particle diameter of 75 μm or less, and sintered by spark plasma sintering (SPS) at a temperature of 600 and a pressure of 50 MPa for 8 minutes, thus preparing a chalcogen-containing compound.

Comparative Example 7: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.13.9.Fe.SUB.0.1.Sb.SUB.2.Te.SUB.17

(21) High purity raw materials Sn shot, Fe powder, Sb shot, and Te shot were weighed in a glovebox at a mole ratio of 13.9:0.1:2:17, put in a carbon crucible, and then charged into a quartz tube. The inside of the quartz tube was vacuumized and sealed. Subsequently, the raw materials were maintained at a constant temperature in an electric furnace at 750 for 12 hours, and then slowly cooled to room temperature. Thereafter, they were heat treated at 640° C. for 48 hours, and the quartz tube in which a reaction was progressed was cooled with water to obtain an ingot. The ingot was finely pulverized to powder with a particle diameter of 75 μm or less, and sintered by spark plasma sintering (SPS) at a temperature of 600° C. and a pressure of 50 MPa for 8 minutes, thus preparing a chalcogen-containing compound.

Example 1: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.13.9.In.SUB.0.1.Sb.SUB.2.Te.SUB.17

(22) A chalcogen-containing compound was prepared by the same method as Comparative Example 1, except that high purity raw materials of Sn shot, In powder, Sb shot, and Te shot were used at the mole ratio of 13.9:0.1:2:17.

Example 2: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.13.8.In.SUB.0.2.Sb.SUB.2.Te.SUB.17

(23) A chalcogen-containing compound was prepared by the same method as Comparative Example 1, except that high purity raw materials of Sn shot, In powder, Sb shot, and Te shot were used at the mole ratio of 13.8:0.2:2:17.

Example 3: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.15.9.In.SUB.0.1.Sb.SUB.2.Te.SUB.19

(24) A chalcogen-containing compound was prepared by the same method as Comparative Example 1, except that high purity raw materials of Sn shot, In powder, Sb shot, and Te shot were used at the mole ratio of 15.9:0.1:2:19.

Example 4: Preparation of a Chalcogen-Containing Compound of V.SUB.1.Sn.SUB.15.8.In.SUB.0.2.Sb.SUB.2.Te.SUB.19

(25) A chalcogen-containing compound was prepared by the same method as Comparative Example 1, except that high purity raw materials of Sn shot, In powder, Sb shot, and Te shot were used at the mole ratio of 15.8:0.2:2:19.

Experimental Examples

(26) 1. Phase Analysis According to XRD Pattern

(27) For the powder chalcogen-containing compound powders prepared in Examples 1 to 4 and Comparative Examples 1 and 2, X-ray diffraction analysis was progressed under the following conditions, and the results are shown in FIG. 3. In the same manner, for the powder chalcogen-containing compound powders prepared in Comparative Examples 3 to 7, X-ray diffraction analysis was progressed and the results are shown in FIG. 4.

(28) For the X-ray diffraction analysis, each chalcogen-containing compound prepared in the examples and comparative examples was properly pulverized and charged into the sample holder of an X-ray diffraction analyzer (Bruker D8-Advance XRD), and X-ray scanned at an interval of 0.02 degrees, with Cu Kα1 (λ=1.5405 Å), an applied voltage of 40 kV, and an applied current of 40 mA.

(29) As shown in FIG. 3, it was confirmed that the chalcogen compounds of Examples 1 to 4 and Comparative Examples 1 and 2 have lattice structures identical to SnTe, which was previously known to have a face-centered cubic lattice structure.

(30) Meanwhile, as shown in FIG. 4, it was confirmed that the chalcogen-containing compound of Comparative Example 4 including In instead of Sb, and the chalcogen-containing compound of Comparative Example 5 without In substitution, also have the same lattices structure as SnTe. However, it was confirmed that although the chalcogen compounds of Comparative Example 3 wherein In is excessively substituted, Comparative Example 6 wherein Sn, In, Sb, Te, and vacancy (V) are included, but the content of the vacancy is less than 1, and Comparative Example 7 wherein a part of Sn is substituted with Fe instead of In, have lattice structures similar to that of SnTe, a composition wherein In is substituted at the Sn site (Sn.sub.0.905In.sub.0.095Te) is mixed. Thus, in the case of Comparative Examples 6 and 7, due to the existence of a secondary phase having a different composition, it is expected that the thermoelectric figure of merit may be deteriorated, compared to the examples.

(31) From the above results, it can be seen that under conditions fulfilling the mole ratio of Sn:Te of (a−x):(a+3) (wherein 14≤a≤16 and 0<x≤0.5), in case a vacancy is included, and a part of Sn is substituted with In, a stable face-centered cubic lattice structure may be formed without formation of secondary phases.

(32) 2. Analysis of Crystal Structure Using TOPAS Program

(33) Using a TOPAS program (R. W. Cheary, A. Coelho, J. Appl. Crystallogr. 25 (1992) 109-121; Bruker AXS, TOPAS 4.2, Karlsruhe, Germany (2009)), the lattice constant (lattice parameter) of each powder chalcogen-containing compound of Examples 1 to 4 and Comparative Examples 1 and 2 was calculated, and the results are shown in the following Table 1. Further, the Rietveld refinement results of the chalcogen-containing compounds of Examples 1 to 4 and Comparative Examples 1 and 2, calculated using the TOPAS program, are shown in the following Table 2.

(34) TABLE-US-00001 TABLE 1 Lattice constant Calculated (Lattice parameter) Vacancy   (Å) concentration Comparative 6.2872 1/17 (0.059) Example 1 Example 1 6.2861 Example 2 6.2853 Comparative 6.2899 1/19 (0.053) Example 2 Example 3 6.2897 Example 4 6.2886

(35) TABLE-US-00002 TABLE 2 Comparative Example Example Comparative Example Example Unit (atomic %) Example 1 1 2 Example 2 3 4 Vacancy (0, 0, 0) 0.0589 0.0589 0.0589 0.0526 0.0526 0.0526 occupancy Sn (0, 0, 0) 0.8235 0.8176 0.8118 0.8421 0.8368 0.8316 occupancy In (0, 0, 0) 0 0.0059 0.0118 0 0.0053 0.0105 occupancy Sb (0, 0, 0) 0.1176 0.1176 0.1176 0.1053 0.1053 0.1053 occupancy Te (0.5, 0.5, 0.5) 1 1 1 1 1 1 occupancy Rwp (weighted 5.096 5.976 5.935 5.373 4.916 5.016 pattern R)

(36) Examining the schemes of the chalcogen-containing compounds with reference to the Tables 1 and 2, and FIG. 2, in the chalcogen-containing compounds of Examples 1 to 4, V (vacancy), Sn, Sb, and In are randomly distributed at the (x, y, z)=(0, 0, 0) site, and Te is distributed at the (0.5, 0.5, 0.5) site. As shown in Table 1, this corresponds to the Rietveld refinement results calculated using the TOPAS program, and the calculated composition is very similar to the initial nominal composition. Thus, it can be seen that in the chalcogen-containing compounds of Examples 1 to 4, a vacancy (V) is included, and a part of Sn is substituted with In, and thus the concentration of Sn decreases.

(37) Referring to Table 1, as the content (x) of In in the face-centered cubic lattice structure increases, a lattice constant gradually decreases (Comparative Example 1>Example 1>Example 2), (Comparative Example 2>Example 3>Example 4). This means that since the radius of Sn.sup.2+ (118 pm) is larger than that of In.sup.3+ (80 pm), as the content of In increases, that is, as the substitution amount of In for Sn increases, the lattice constant decreases.

(38) It can also be confirmed that in case the rate of [Sn]/[Sb] increases, the lattice constant increases because the radius of Sn.sup.2+ (118 pm) is larger than that of Sb.sup.3+ (76 pm) (Comparative Example 2>Comparative Example 1), (Example 3>Example 1), (Example 4>Example 2).

(39) 2. Temperature Dependency of Electrical Conductivity

(40) For the chalcogen-containing compound specimens prepared in Examples 1 to 4 and Comparative Examples 1 to 5, electrical conductivities were measured according to temperature change and are shown in FIG. 5. The electrical conductivity was measured in the temperature range of 100 to 500° C. through a four-probe direct current method, using a resistivity meter ZEM-3 from ULVAC.

(41) Referring to FIG. 5, in the case of Comparative Examples 1 and 2, as the content of Sn increases, electrical conductivity increases. The reason is that Sn donates one less electron compared to Sb (Sn.sup.2+ vs. Sb.sup.3+), and thus, as the content of Sn increases, the number of donated electrons decreases, and to the contrary, the concentration of main charge carrier holes increases.

(42) Further, in the case of Comparative Example 3, In is substituted at the Sn site to fill the intrinsic vacancy of Sn, thus decreasing the hole concentration, and remaining In acts as In.sup.3+ to increase the number of donated electrons, thereby additionally decreasing the concentration of main charge carrier holes. As a result, electrical conductivity rapidly decreased. Further, the chalcogen-containing compound of Comparative Example 3 exhibits the properties of a semiconductor with a tendency of an increase in electrical conductivity according to an increase in measurement temperature, unlike Comparative Examples 1 and 2 and Examples 1 to 4.

(43) In addition, Comparative Example 4 includes In without including Sb, unlike Comparative Example 5, and due to the low atomic number of In compared to Sb, the number of donated electrons deceases, and to the contrary, the concentration of main charge carrier holes increases, thus exhibiting high electrical conductivity compared to Comparative Example 5.

(44) Meanwhile, comparing Examples 1 and 2 with Comparative Example 1, and Examples 3 and 4 with Comparative Example 2, as the Sn site is substituted with In, the intrinsic vacancy of Sn is filled to decrease the concentration of holes, and thus, electrical conductivity relatively decreases.

(45) 3. Temperature Dependency of Seebeck Coefficient

(46) For the chalcogen-containing compound specimens prepared in Examples 1 to 4 and Comparative Examples 1 to 5, Seebeck coefficients (S) were measured according to temperature change, and the results are shown in FIG. 6. The Seebeck coefficient was measured in the temperature range of 100 to 500° C. by a differential voltage/temperature technique, using measuring equipment of ZEM-3 from ULCAC.

(47) As shown in FIG. 6, Examples 1 to 4 and Comparative Examples 1 to 5 exhibit positive (+) Seebeck coefficients, and thus it can be seen that the major electric charge carriers of the materials are holes, thus exhibiting the properties as P-type semiconductor materials.

(48) Comparative Examples 1 and 2 showed a tendency of a decrease in the Seebeck coefficient according to an increase in the Sn content.

(49) Meanwhile, Comparative Example 1 and Examples 1 and 2 showed a tendency of an increase in the Seebeck coefficient according to the substitution of In at the Sn site. Similarly, Comparative Example 2 and Examples 3 and 4 showed a tendency of an increase in the Seebeck coefficient according to the substitution of In at the Sn site. The reason is that the Seebeck coefficient has an opposite tendency to electrical conductivity in terms of a charge carrier concentration (as the concentration of charge carriers is higher, electrical conductivity increases but the Seebeck coefficient decreases).

(50) Further, since Comparative Example 3 shows the electrical conductivity properties of a semiconductor as confirmed in FIG. 5, it showed a different tendency from the Seebeck coefficient change tendencies of Comparative Examples 1 and 2 and Examples 1 to 4, and Comparative Example 4 showed a low Seebeck coefficient due to high electrical conductivity.

(51) 4. Temperature Dependency of Power Factor

(52) For the chalcogen-containing compound specimens prepared in Examples 1 to 4 and Comparative Examples 1 to 5, power factors were calculated according to temperature change, and the results are shown in FIG. 7.

(53) The power factor is defined as Power Factor (PF)=σS.sup.2, and it was calculated using the values of σ (electric conductivity) and S (Seebeck coefficient) shown in FIGS. 5 and 6.

(54) As shown in FIG. 7, it was confirmed that Comparative Examples 1 and 2 showed a low power factor at a low temperature region, but the power factor tends to increase toward a high temperature region.

(55) And, Comparative Example 3 showed a low power factor due to low electrical conductivity and low Seebeck coefficient. Comparative Example 4 showed a high power factor due to high electrical conductivity despite a low Seebeck coefficient, but the power factor tended to decrease as a measurement temperature increases.

(56) 5. Temperature Dependency of Thermal Conductivity

(57) For the chalcogen-containing compound specimens prepared in Examples 1 to 4 and Comparative Examples 1 to 5, thermal conductivities were measured according to temperature change, and the results are shown in FIG. 8.

(58) Specifically, for the measurement of thermal conductivity, thermal diffusivity (D) and heat capacity (C.sub.p) were measured by a laser flash method, using thermal conductivity measuring equipment of LFA457 from Netzsch Company, and the measured values were applied in the following Mathematical Formula 2 to calculate thermal conductivity (k).
Thermal conductivity (k)=DρC.sub.p  [Mathematical Formula 2]

(59) In Mathematical Formula 2, D is thermal diffusivity, C.sub.p is heat capacity, and p is the density of a sample measured by Archimedes's principle.

(60) And, total thermal conductivity (k=k.sub.L+k.sub.E) is divided into lattice thermal conductivity (k.sub.L) and thermal conductivity (k.sub.E) calculated according to Wiedemann-Franz law (k.sub.E=LσT), wherein, as the Lorentz number (L), a value calculated from the Seebeck coefficient according to temperature was used.

(61) Referring to FIG. 8, it was confirmed that in Comparative Examples 1 and 2, as the content of Sn increases, total thermal conductivity increases due to an increase in charge concentration, but Examples 1 to 4 showed relatively low thermal conductivity compared to Comparative Examples 1 and 2. This means that according to In substitution, hole charge concentration decreased, and thus thermal conductivity to which charge carrier contributes decreased. It has the same tendency as the electrical conductivity of FIG. 5.

(62) 6. Temperature Dependency of Thermoelectric Figure of Merit (ZT)

(63) For the chalcogen-containing compound specimens prepared in Examples 1 to 4 and Comparative Examples 1 to 5, the thermoelectric figure of merit was calculated according to temperature change, and the results are shown in FIG. 9.

(64) The thermoelectric figure of merit is defined by ZT=S.sup.2σT/k, and it was calculated using the S (Seebeck coefficient), σ (electric conductivity), T (absolute temperature), and k (thermal conductivity) values obtained in experimental examples.

(65) Referring to FIG. 9, Comparative Examples 1 and 2 showed low ZT in the low temperature region due to the increased Sn content, but ZT increased toward a high temperature region, while Examples 1 to 4 showed relatively high ZT from the low temperature region as the Sn site is substituted with In, and showed similar or slightly higher ZT in the high temperature region. Particularly, Example 3 showed high ZT of about 0.94 (at 500° C.).

(66) 7. Average Thermoelectric Properties

(67) Based on the above experimental results, average power factor (PF.sub.average), average thermal conductivity (K.sub.tot,average), and average thermoelectric figure of merit (ZT.sub.average) at 100 to 500° C. were calculated. The results are shown in the following Table 3 and FIGS. 10 to 13.

(68) FIG. 10 is a graph showing the average values of power factors according to an indium substitution amount in the chalcogen-containing compounds of Examples 1 and 2 and Comparative Example 1, namely, the x value in Chemical Formula 1, and FIG. 11 is a graph showing the average values of thermoelectric figures of merits of these compounds. Further, FIG. 12 is a graph showing the average values of power factors according to an indium substitution amount in the chalcogen-containing compounds of Examples 3 and 4 and Comparative Example 2, and FIG. 13 is a graph showing the average values of thermoelectric figures of merits of these compounds. In FIGS. 10 to 13, the unit of the indium substitution amount is a mole.

(69) TABLE-US-00003 TABLE 3 100~500° C. average thermoelectric properties PF.sub.average K.sub.tot, average (μW/cmK.sup.2) (W/mK) ZT.sub.average ZT.sub.max Comparative 14.45 2.33 0.41 0.91 Example 1 Example 1 16.41 1.91 0.52 0.94 Example 2 16.72 1.76 0.52 0.90 Comparative 14.15 2.54 0.39 0.91 Example 2 Example 3 16.44 2.06 0.49 0.94 Example 4 16.79 1.83 0.53 0.91

(70) Referring to the average thermal conductivity at 100 to 500 in Table 3, it can be confirmed that in Examples 1 to 4, the average thermal conductivity decreased 18˜28%, compared to Comparative Examples 1 and 2.

(71) Meanwhile, from the results of average power factor of FIG. 10 (Examples 1 and 2 and Comparative Example 1) and FIG. 12 (Examples 3 and 4 and Comparative Example 2), it was confirmed that in case In is substituted at the Sn site, as the In substitution amount increases, the average power factor tends to be improved, particularly in the low temperature region. When calculating the average power factor in the 100 to 500° C. region with reference to Table 3, it can be confirmed that the average power factor at 100 to 500° C. of Examples 1 to 4 increased about 16˜19%, compared to Comparative Examples 1 and 2.

(72) Further, from the results of average thermoelectric figure of merit (ZT.sub.ave.) of FIG. 11 (Examples 1 and 2 and Comparative Example 1) and FIG. 13 (Examples 3 and 4 and Comparative Example 2), it can be confirmed that when In is substituted at the Sn site, as the substitution amount increases, the average value of thermoelectric figure of merit also increases. When calculating with reference to Table 3, it can be confirmed that the average ZT value at 100 to 500 of Examples 1 to 4 increased about 27˜36% compared to Comparative Examples 1 and 2.