Compound semiconductor and use thereof

Abstract

A compound semiconductor which has an improved thermoelectric performance index together with excellent electrical conductivity, and thus may be utilized for various purposes such as a thermoelectric conversion material of thermoelectric conversion devices, solar cells, and the like, and to a method for preparing the same.

Claims

1. A compound semiconductor represented by the following Chemical Formula 1:
S.sub.xCO.sub.4Sb.sub.12-y-zQ.sub.ySn.sub.z  [Chemical Formula 1] wherein in Chemical Formula 1, Q comprises at least one among O, Se, and Te, and x, y, and z are denote a molar ratio, wherein 0<x≤1, 0<y<12, 0<z<12, 0<y+z<12, and y≥3x, wherein the compound semiconductor is one in which S is filled as a filler in an n-type Co—Sb skutterudite which is simultaneously substituted with a chalcogen element Q and Sn at Sb sites.

2. The compound semiconductor of claim 1, wherein in Chemical Formula 1, y≥3x when 0<y+z<1.

3. The compound semiconductor of claim 1, wherein in Chemical Formula 1, y=3x+z when 1≤y+z<12.

4. The compound semiconductor of claim 1, wherein in Chemical Formula 1, x is in the range of 0.1≤x≤0.2.

5. The compound semiconductor of claim 1, wherein in Chemical Formula 1, y and z are in the range of 0.6≤y≤0.8 and 0.05≤z≤0.2, respectively.

6. The compound semiconductor of claim 1, wherein in Chemical Formula 1, Q is Te.

7. A method for preparing the compound semiconductor of claim 1 comprising: mixing S, Co, Sb, Q, and Sn in a content so as to satisfy a compound composition of the following Chemical Formula 1 to provide a mixture; and thermally treating the mixture:
S.sub.xCO.sub.4Sb.sub.12-y-zQ.sub.ySn.sub.z  [Chemical Formula 1] wherein in Chemical Formula 1, Q comprises at least one among O, Se, and Te, and x, y, and z denote a molar ratio, wherein 0<x≤1, 0<y<12, 0<z<12, 0<y+z<12, and y≥3x.

8. The method for preparing the compound semiconductor of claim 7, wherein thermally treating the mixture is performed at a temperature of 400° C. to 800° C.

9. The method for preparing the compound semiconductor of claim 7, further comprising a cooling step after thermally treating the mixture.

10. The method for preparing the compound semiconductor of claim 7, further comprising a pressure-sintering step after thermally treating the mixture.

11. A thermoelectric conversion device comprising the compound semiconductor according to claim 1.

12. A solar cell comprising the compound semiconductor according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph showing evaluation results of the lattice thermal conductivity (k.sub.L) of compound semiconductors of Examples 1 to 3 and Comparative Examples 1 to 6.

(2) FIG. 2 is a graph showing evaluation results of the lattice thermal conductivity (k.sub.L) of compound semiconductors of Examples 4 to 6 and Comparative Examples 1 to 6.

(3) FIG. 3 is a graph showing evaluation results of the thermal performance index (ZT) of the thermoelectric device including compound semiconductors of Examples 1 to 3 and Comparative Examples 1 to 6.

(4) FIG. 4 is a graph showing evaluation results of the electrical conductivity (σ) of compound semiconductors of Examples 4 to 6 and Comparative Example 3

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) The present invention will be described in more detail by way of examples. However, these examples are given for illustrative purposes only, and the scope of the invention is not intended to be limited by these examples

EXAMPLE 1

(6) In order to synthesize S.sub.0.2Co.sub.4Sb.sub.11.35Te.sub.0.6Sn.sub.0.05, Sn, S, Co, Sb, and Te in a powder form were weighed, and then they were put into an alumina mortar and mixed. The mixed materials were put into an ultra hard mold and formed into a pellet, which was put into a fused silica tube and vacuum-sealed. Then, the resultant product was put into a box furnace and heated at 680° C. for 15 hours to give S.sub.0.2Co.sub.4Sb.sub.11.35Te.sub.0.6Sn.sub.0.75. Thereafter, the resultant compound was slowly cooled down to room temperature, charged into a graphite mold for spark plasma sintering, and then subjected to spark plasma sintering at a temperature of 650° C. under a pressure of 50 MPa for 10 minutes. The relative density of the thus obtained compound semiconductor was measured to be 98% or more.

EXAMPLE 2

(7) A compound semiconductor was prepared in the same manner as in Example 1, except that the mixture composition was changed to S.sub.0.2Co.sub.4Sb.sub.11.325Te.sub.0.6Sn.sub.0.75.

EXAMPLE 3

(8) A compound semiconductor was prepared in the same manner as in Example 1, except that the mixture composition was changed to S.sub.0.2Co.sub.4Sb.sub.11.3Te.sub.0.6Sn.sub.0.1.

EXAMPLE 4

(9) A compound semiconductor was prepared in the same manner as in Example 1, except that the mixture composition was changed to S.sub.0.2Co.sub.4Sb.sub.11.3Te.sub.0.65Sn.sub.0.05.

EXAMPLE 5

(10) A compound semiconductor was prepared in the same manner as in Example 1, except that the mixture composition was changed to S.sub.0.2Co.sub.4Sb.sub.11.2Te.sub.0.7Sn.sub.0.1.

EXAMPLE 6

(11) A compound semiconductor was prepared in the same manner as in Example 1, except that the mixture composition was changed to S.sub.0.2Co.sub.4Sb.sub.11Te.sub.0.8Sn.sub.0.2.

Comparative Example 1

(12) A compound semiconductor was prepared in the same manner as in Example 1, except that S, Co, Sb, and Te were prepared as reagents, and the mixture composition was changed to S.sub.0.2Co.sub.4Sb.sub.11.6Te.sub.0.4.

(13) However, in the composition of the compound thus prepared, S.sup.2− was unstable due to an imbalance of charge balance and a part of S existed as a S-rich phase such as CoSSb. Thus, the filling of S was not completely achieved.

Comparative Example 2

(14) A compound semiconductor was prepared in the same manner as in Example 1, except that S, Co, Sb, and Te were prepared as reagents, and the mixture composition was changed to S.sub.0.2Co.sub.4Sb.sub.11.5Te.sub.0.5. However, also in the composition of the compound thus prepared, the filling of S was not completely achieved due to an imbalance of charge balance.

Comparative Example 3

(15) A compound semiconductor was prepared in the same manner as in Example 1, except that S, Co, Sb, and Te were prepared as reagents, and the mixture composition was changed to S.sub.0.02, Co.sub.4Sb.sub.11.4Te.sub.0.6.

Comparative Example 4

(16) A compound semiconductor was prepared in the same manner as in Example 1, except that S, Co, Sb, and Te were prepared as reagents, and the mixture composition was changed to S.sub.0.05Co.sub.4Sb.sub.11.4Te.sub.0.6.

Comparative Example 5

(17) A compound semiconductor was prepared in the same manner as in Example 1, except that S, Co, Sb, and Te were prepared as reagents, and the mixture composition was changed to S.sub.0.1Co.sub.4Sb.sub.11.4Te.sub.0.6.

Comparative Example 6

(18) A compound semiconductor was prepared in the same manner as in Example 1, except that S, Co, Sb, and Te were prepared as reagents, and the mixture composition was changed to Co.sub.4Sb.sub.11.275Te.sub.0.6Sn.sub.0.125.

Experimental Example 1: Measurement of Lattice Thermal Conductivity

(19) The lattice thermal conductivity of the compound semiconductors obtained in the examples and comparative examples was measured, and the results are shown in FIGS. 1 and 2.

(20) Specifically, the compound semiconductors obtained in the examples and comparative examples were processed into a coin-type having a diameter of 12.7 mm and a height of 1.5 mm to prepare specimens. Then, the thermal conductivity of the specimens was calculated from the measured values of thermal diffusivity, specific heat, and density by means of a laser flash (Netzsch, LFA-457) in the range of 50° C. to 500° C. Then, the Lorenz number was calculated and the value thereof was applied to the calculated thermal conductivity to obtain lattice thermal conductivity.

(21) As a result of the experiment, as illustrated in FIG. 1, Examples 1 to 3 exhibited reduced thermal conductivities over the entire temperature measurement section in comparison to those of Comparative Examples 1 to 5 in which Sn was not substituted. These results were obtained due to the fact that the lattice thermal conductivity was reduced when Sn was substituted at Sb sites of S-filled Skutterudite. In addition, Examples 1 to 3 showed remarkably reduced lattice thermal conductivities in comparison with that of Comparative Example 6 in which S was not filled but Te and Sn were substituted at Sb sites. From these results, it can be confirmed that the reduction effect in the lattice thermal conductivity due to the filling of S is remarkable.

(22) Further, as illustrated in FIG. 2, Examples 4 to 6 in which the substitution amounts of Sn were increased showed reduced lattice thermal conductivity through a control with the substitution amount of Te, in comparison with those of Comparative Examples 1 to 6.

Experimental Example 2: Thermoelectric Performance Index (ZT)

(23) The thermoelectric performance index of the compound semiconductors obtained in Examples 1 to 3 and Comparative Examples 1 to 6 was measured, and the results are shown in Tables 1 and 2 and FIG. 3.

(24) The compound semiconductors obtained in Examples 1 to 3 and Comparative Examples 1 to 6 were processed into a rectangular-type having a length of 3 mm, a width of 3 mm, and a height of 12 mm to prepare specimens. Then, the electrical conductivity and the Seebeck coefficient of the specimens were measured using ZEM-3 (Ulvac-Rico, Inc) in the range of 50° C. to 500° C.

(25) Next, the thermoelectric performance index (ZT) was calculated from the measured electrical conductivity, Seebeck coefficient, and thermal conductivity value of Experimental Example 1 described above by using Mathematical Equation 1 below.
ZT=σS.sup.2T/K  [Mathematical Equation 1]

(26) Herein, ZT represents a thermoelectric performance index, σ represents electrical conductivity, S represents a Seebeck coefficient, T represents temperature, and κ represents thermal conductivity.

(27) TABLE-US-00001 TABLE 1 Temperature Examples Comparative Examples (° C.) 1 2 3 1 2 3 4 5 6  50 0.27 0.29 0.28 0.25 0.28 0.25 0.21 0.24 0.187 100 0.37 0.39 0.38 0.34 0.38 0.34 0.29 0.33 0.254 200 0.60 0.62 0.61 0.55 0.59 0.55 0.48 0.54 0.415 300 0.84 0.87 0.87 0.77 0.82 0.77 0.68 0.76 0.597 400 1.05 1.11 1.12 0.96 1.03 0.99 0.87 0.97 0.781 500 1.22 1.32 1.33 1.06 1.19 1.19 1.03 1.14 0.944

(28) As a result, as illustrated in Tables 1 and 2 and FIG. 3, the compound semiconductors obtained in Examples 1 to 3 had lowered lattice thermal conductivity and thereby showed a high thermal performance index over the entire temperature measurement section in comparison with those of Comparative Examples 1 to 6.

Experimental Example 3: Measurement of Electrical Conductivity

(29) The electrical conductivity of the compound semiconductors obtained in the examples and comparative examples was measured, and the results are shown in FIG. 4 below.

(30) The electrical conductivity was measured using ZEM-3 (Ulvac-Rico, Inc) equipment.

(31) As a result, as illustrated in FIG. 4, the compound semiconductors obtained in Examples 4 to 6 showed increased electrical conductivity at the entire temperature measurement section in comparison with that of Comparative Example 3. From this, it can be confirmed that the electrical conductivity, which could be lowered as Sn was substituted at Sb sites of S-filled skutterudite, was increased through the substitution with Te.