KR101574973B1 - Antimony-doped thermoelectric solid solution materials and method for manufacturing the same - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to a solid solution thermoelectric material doped with antimony and a method of manufacturing the same. More particularly, the present invention relates to a solid solution thermoelectric material doped with antimony capable of improving thermoelectric performance and a method of manufacturing the same.
According to the present invention, by applying the method of performing the solid-phase reaction after mixing the raw material powders, it is possible to naturally produce a solid solution type thermoelectric material, thereby remarkably improving the thermoelectric performance.
Further, by applying the hot compression process under the optimum conditions, a molding agent having a desired density can be produced.
In addition, according to the present invention, a thermoelectric material in a solid solution state can be produced only by mixing raw material powders and reacting in a solid state, so that a thermoelectric material having improved performance can be manufactured at low cost.
According to the present invention, the electrical conductivity and the Seebeck coefficient of the thermoelectric material can be optimized by doping Sb into the solid solution thermoelectric material.

Description

TECHNICAL FIELD The present invention relates to an antimony-doped solid solution thermoelectric material and a method of manufacturing the same. BACKGROUND ART < RTI ID = 0.0 > [0002] <

TECHNICAL FIELD The present invention relates to a solid solution thermoelectric material doped with antimony and a method of manufacturing the same. More particularly, the present invention relates to a solid solution thermoelectric material doped with antimony capable of improving thermoelectric performance and a method of manufacturing the same.

In general, research and research on efficient energy conversion materials are actively being carried out with the recent interest in development and saving of alternative energy. In particular, research on thermoelectric materials, which are materials for converting thermal energy and electric energy, is accelerated.

A thermoelectric material is a metal or a ceramic material having a function of directly converting heat into electricity or electric heat, and it is advantageous that power generation is possible without moving parts if only temperature difference is given.

The thermoelectric materials were developed from the late 1930s after the discovery of the thermoelectric phenomenon Seebeck effect, Peltier effect and Thomson effect in the early 19th century, along with the development of semiconductors, .

Recently, thermoelectric materials have been used as special power devices such as wallpaper for the mountain, space, and military using thermoelectric power generation characteristics. In addition, thermoelectric cooling has been widely used in semiconductor laser diodes, infrared ray detection devices, Small cooling columns and so on.

The efficiency of the thermoelectric material is evaluated as a dimensionless figure of merit, which is defined as ZT = α ² σT / (κ _E + κ _L ). α is the Seebeck coefficient, σ is the electrical conductivity, κ _E is the electronic thermal conductivity, and κ _L is the lattice thermal conductivity. Therefore, in order to optimize the thermoelectric property, it is necessary to increase the power factor (PF = α2σ) while decreasing the κ _L while trying to generate Phonon-Glass and Electron-Crystal (PGEC). The material factor β = (m ^* / m _e ) ^3/2 μ k _L ^-1 can be used as a criterion for selecting thermoelectric materials (where m ^* is the density-of-states effective mass and m _e is the mass of electron, and mu is carrier mobility). As a result, it is necessary to have low lattice conductivity and high carrier mobility in order to be a high performance thermoelectric material.

Among the materials with high thermoelectric performance index, materials that are currently widely used are Bi ₂ Te ₃ and solid solution materials thereof. Particularly, in the case of the solid solution, thermal conductivity decreases due to the effect of phonon scattering due to the point defect, thereby improving the figure of merit. However, when segregation occurs due to failure to form a uniform solid solution, There is a problem that a uniform solid solution is formed (Patent No. 10-0440268)

On the other hand, Bi ₂ Te ₃ is very expensive using Te, which is a scarce resource, and there is a problem of using Bi, which is a toxic substance.

Recently, magnesium compounds Mg ₂ B ^IV (B ^IV = Si, Ge, Sn) and their solid solutions have been attracting attention as promising thermoelectric materials. They exhibit excellent thermoelectric properties in the mid-temperature range of 500K to 800K and are known as eco-friendly and economical thermoelectric materials. The β value of the magnesium compound Mg ₂ B ^IV is 3.7-14, which is much higher than that of iron silicide (0.05-0.8) and silicon-germanium alloy (1.2-2.6). The Mg ₂ Si-Mg ₂ Ge solid solution can also be expected to replace the Ge site and reduce thermal conductivity due to phonon scattering enhanced by the substituted Si sites.

However, when the Mg alloy is dissolved in the solid solution production process, there is a problem that Mg is volatilized and oxidized, the melting point of Mg, Si, and Ge is different, and gravity separation, so that it is difficult to control the overall composition. It is necessary.

Korean Patent No. 10-0440268

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art, and it is an object of the present invention to provide a solid solution thermoelectric material capable of improving thermoelectric performance by optimizing electric conductivity and a Seebeck coefficient, and a method of manufacturing the same.

According to the present invention, there is provided a method of manufacturing a magnetic powder, comprising the steps of: (a) mixing a raw powder containing Mg powder, Si powder, Ge powder and Sb powder; A solid phase reaction step (step b) in which the powder mixed in step a) is reacted in a solid state through heat treatment; And a step (c) of thermally compressing the powder synthesized in the step (b), thereby providing a method of manufacturing antimony-doped solid solution thermoelectric materials.

The mixing step (step a) may be carried out according to the stoichiometric composition of Mg ₂ Si _1-x Ge _x Sb _m (0 <x <1, 0 < _m ≦ 0.1). More preferably, they can be mixed according to the stoichiometric composition of Mg ₂ Si _1-x Ge _x Sb _m (0.3? _X? 0.7, 0.005? _M ? 0.03). If the amount of antimony exceeds the above range, it may be difficult to optimize the electric conductivity and the Seebeck coefficient of the thermoelectric material.

The solid phase reaction step may be a step of synthesizing Sb-doped Mg ₂ Si-Mg ₂ Ge solid solution powder.

The solid phase reaction step (step b) in which the powders mixed in step a) are reacted in a solid state through heat treatment is a method of performing a solid phase reaction after mixing the raw material powders. The solid phase reaction naturally forms Sb- . As a result, the performance of the thermoelectric material can be improved and this characteristic can not be predicted by the conventional solid-phase reaction method in which the solid state material is simply reacted.

The solid phase reaction step (step b) may be carried out at a temperature ranging from 773 to 973K for 1 to 10 hours. It is difficult to form an expected solid solution when a solid phase reaction is performed at a temperature lower than the above range for a short time and a manufacturing cost is increased when a solid phase reaction is performed at a temperature higher than the above range for a long time, A problem may occur that the second phase is formed or Mg is oxidized or volatilized.

The hot compression step (step c) after the solid phase reaction step can be carried out at a pressure of 10 to 100 MPa and a temperature range of 973 to 1173K. When hot compression is performed at a pressure lower than the above-mentioned range, it is difficult to mold at a desired density. When hot compression is performed at a pressure higher than the above range and at a high temperature, manufacturing cost increases and a second phase is formed.

And cold compressing the mixed raw material powder before performing the solid phase reaction step. The cold compression process may be performed at a pressure of 10 to 1000 MPa. The cold compression process is intended to promote the diffusion of the raw material powders in the subsequent solid phase reaction by widening the contact area of the raw material powders. When the cold compression process is not performed, the solid phase reaction partially progresses, A synthesis result can not be obtained and there is a problem that unreacted raw material remains. When cold compression is performed at a pressure lower than this pressure, solid phase reaction and diffusion promotion effect by cold compression can not be obtained, and in case of performing cold compression at a higher pressure, the cost is increased.

According to the present invention, there is provided a method for producing a silicon carbide powder, comprising the steps of: mixing a raw material powder containing Mg powder, Si powder and Ge powder; A solid phase reaction step in which the powder mixed in the mixing step is reacted in a solid state through heat treatment; Doping Sb powder after the solid phase reaction step; And a step of thermally compressing the synthesized powder through the solid phase reaction step and doping step, thereby providing a method of manufacturing an antimony-doped solid solution thermoelectric material.

The Mg powder, Si powder, Ge powder and Sb powder can be added in an amount corresponding to the stoichiometric composition of Mg ₂ Si _1-x Ge _x Sb _m (0 <x <1, 0 < _m ≦ 0.1) have. More preferably, it can be added in an amount corresponding to the stoichiometric composition of Mg ₂ Si _1-x Ge _x Sb _m (0.3? _X? 0.7, 0.005? _M ? 0.03). Since the contents of the solid phase reaction step and the hot compression step are the same as those described above, they are omitted here.

According to the present invention, there is provided a solid-state thermoelectric material as described above, wherein the solid-solution thermoelectric material is a solid solution comprising a composition of Mg ₂ Si _1-x Ge _x Sb _m (0 <x <1, 0 < _m ≦ 0.1) A solid solution thermoelectric material can be provided.

The thermoelectric material may exhibit n-type conduction.

The thermoelectric material may have a composition of Mg ₂ Si _1-x Ge _x Sb _m (0.3? _X? 0.7, 0.005? _M ? 0.03).

In particular, the thermoelectric material may be composed of Mg ₂ Si _0.5 Ge _0.5 Sb _0.02 .

According to the present invention, by applying the method of performing the solid-phase reaction after mixing the raw material powders, it is possible to naturally produce a solid solution type thermoelectric material, thereby remarkably improving the thermoelectric performance.

Further, by applying the hot compression process under the optimum conditions, a molding agent having a desired density can be produced.

In addition, according to the present invention, a thermoelectric material in a solid solution state can be produced only by mixing raw material powders and reacting in a solid state, so that a thermoelectric material having improved performance can be manufactured at low cost.

According to the present invention, the electrical conductivity and the Seebeck coefficient of the thermoelectric material can be optimized by doping Sb into the solid solution thermoelectric material.

FIGS. 1A and 1B show the results of X-ray diffraction analysis of the produced specimen.
2 is a graph showing the change in lattice constant of the prepared specimen.
FIGS. 3A and 3B are the results of measuring the electrical conductivity according to the temperature of the produced specimen.
FIGS. 4A and 4B are the results of measuring the Seebeck coefficient according to the temperature of the produced specimen.
5A to 5C are measurement results of the thermal conductivity of the prepared specimen according to the temperature.
FIGS. 6A and 6C are the results of calculating the dimensionless thermoelectric performance index according to the temperature of the produced specimen.

Hereinafter, the present invention will be described in more detail by way of examples. The objects, features and advantages of the present invention will be readily understood through the following examples. The present invention is not limited to the embodiments described herein but may be embodied in other forms. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Therefore, the scope of the present invention should not be limited by the following examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, embodiments of the present invention will be described in detail.

First, high purity Mg (99.99%, <149 μm), Si (99.99%, <45 μm), Ge (99.99%, <45 μm) and Sb (99.999% Respectively.

The amount of each powder was determined according to the stoichiometric ratio of Mg ₂ Si _1-x Ge _x Sb _m (0.3? _X? 0.7, m = 0, 0.005, 0.01, 0.02 0.03).

The powder mixed at the above ratio was cold-pressed at 600 MPa pressure to form a pellet. By performing such a cold compression process, the contact area of the raw material powders can be widened, thereby promoting the diffusion between the raw material powders in a subsequent solid phase reaction process. In the case where the cold compression process is not carried out, the solid phase reaction partially progresses, and as a result, a homogeneous synthesis result as a whole can not be obtained, and unreacted raw material may remain.

The raw material subjected to the cold pressing process was charged into an alumina crucible and subjected to solid phase reaction (SSR) under vacuum at 773 K for 6 hours. The synthesized powders were loaded into a cylindrical graphite die with an internal diameter of 10 mm, and hot - pressed (HP) under vacuum at a temperature of 1073 K and a pressure of 70 MPa for 2 hours to produce a solid solution thermoelectric material.

The solid solution thermoelectric material according to one embodiment of the present invention may be a method of mixing the doping elements Sb together in the raw material mixing step as in the above method. After the solid solution is formed through the solid phase reaction, the doping element Sb ) May also be applied.

Various physical properties were measured on the specimens prepared by the above method.

Solid phase and lattice constants synthesized by X-ray diffractometer (XRD, Bruker D8-Advance) using Cu K _α radiation (40 kV, 30 mA) were analyzed. The diffraction pattern was measured in the θ-2θ mode (10 to 90 ° 2θ) (step size 0.02 °, scan speed 0.4 sec / step, wave length of 0.15405 nm). For the measurement of the Seebeck coefficient and the electric conductivity, the hot compacted compact was cut into a rectangular shape (3 mm x 3 mm x 9 mm), and the disk shape (thickness) was measured to measure the thermal conductivity and Hall effect Diameter 10 mm x thickness 1 mm). Hall effect measurements were performed at room temperature using the van der Pauw method at constant magnetic field (1 T) and current (50 mA). The Seebeck coefficient and electrical conductivity were measured by a temperature differential method and a 4-probe method using a ZEM-3 (Ulvac-Riko) instrument in a helium atmosphere. Thermal conductivity was estimated from thermal diffusivity, specific heat and density measurements using a laser flash TC-9000H (Ulvac-Riko) in vacuum.

FIGS. 1A and 1B are X-ray diffraction analysis results of the specimen synthesized by the solid-phase reaction. According to the stoichiometric composition of the prepared specimens, Mg ₂ Si _1-x Ge _x Sb _m (0.3? _X? 0.7, m = 0, 0.005, 0.01, 0.02 0.03) The pattern of synthesized solid solution (specimen) was consistent with the standard diffraction peaks of Mg ₂ Si and Mg ₂ Ge. That is, all peaks located between pure Mg ₂ Si and Mg ₂ Ge. As a result, Mg ₂ Si _1-x Ge _x solid solution doped with Sb was successfully synthesized by SSR and HP, and no other secondary phase was formed. These results are due to the fact that the cold compression process was performed prior to the solid phase reaction by heat treatment to promote the reaction and diffusion of the raw material powders. The diffraction peaks shifted slightly to lower angles as the Ge content increased, indicating that the lattice constant was increased by solid solution between Mg ₂ Si and Mg ₂ Ge.

2 shows the change in lattice constant of the prepared specimen. In Fig. 2, x represents the Ge content. Fig. 2 is a graph showing the relationship between the dielectric constant of Mg ₂ Si _1-x Ge _x and Mg ₂ Si _1-x Ge _x Sb _m Ge fraction. As shown in FIG. 2, the lattice constant increased linearly with increasing Ge content. The specimens without doping with Sb increased from 0.6367 nm to 0.6383 ㎚ and the specimens doped with Sb showed slightly higher values. This is due to the lattice constants of Mg ₂ Si (0.6352 nm) and Mg ₂ Ge (0.6392 nm) confirmed in previous studies and consequently satisfies Begard's law, and Mg ₂ Si _1-x Ge _x and Indicates that the solid solution of _{Mg 2 Si 1-x Ge x} Sb m was formed well (Ref [19]:.. . E. Ratai, MP Augustine and SM Kauzlarich, J. Phys Chem B 107, 12573 (2003),. Ref. [20] F. Vazquez, RA Forman and M. Cardona, Phys. Rev. 176 , 905 (1968).) As a result, it can be seen that the Ge atoms were dissolved in the Si sites. In addition, it can be seen that the Si or Ge site was replaced with Sb atoms, but the lattice constant was slightly increased because the Sb doping concentration was not high.

Table 1 shows the electron mobility at room temperature for the sample prepared by the above method.

Specimen Hall coefficient
[cm ³ C ^-1 ] Mobility
[cm ² V ^-1 s ^-1 ] Carrier concentration
[cm ^-3 ] Mg ₂ Si _0.7 Ge _0.3 -15.47 114 4.0x10 ¹⁷ Mg ₂ Si _0.7 Ge _0.3 : Sb _0.02  -0.0027 0.9 2.2x10 ²¹ Mg ₂ Si _0.5 Ge _0.5 -8.44 28 7.3x10 ¹⁷ Mg ₂ Si _0.5 Ge _0.5 : Sb _0.02 -0.003 0.88 2.0x10 ²¹ Mg ₂ Si _0.3 Ge _0.7 5.55 4.1 1.1x10 ¹⁸ Mg ₂ Si _0.3 Ge _0.7 : Sb _0.02  -0.0019 0.2 3.2x10 ²¹ Mg ₂ Si _0.5 Ge _0.5 : Sb _0.005 -0.044 4.2 1.4x10 ²⁰ Mg ₂ Si _0.5 Ge _0.5 : Sb _0.01 -0.004 0.9 1.5x10 ²¹ Mg ₂ Si _0.5 Ge _0.5 : Sb _0.02 -0.003 0.88 2.0x10 ²¹ Mg ₂ Si _0.5 Ge _0.5 : Sb _0.03 -0.0026 0.93 2.3x10 ²¹

Specimens without doping with Sb showed n-type conductivity at x = 0.3-0.5, but transitioned to p-type at room temperature at x≥0.7. This is due to the inherent characteristics of Mg ₂ Ge, a p-type semiconductor. However, all Sb doped specimens showed n-type conduction characteristics, which means that most carriers are electrons. The carrier concentration is from 4.0 x 10 ¹⁷ cm ^-3 by a Sb-doped 3.2 x 10 ²¹ cm ^-3 and the carrier concentration also increased as the Sb content increased. Therefore, for Sb atoms, Mg ₂ Si _1-x Ge _x solid solution type dopant (donor). However, the carrier mobility is reduced by Sb doping, which is a typical behavior of the semiconductor caused by ionized impurity scattering. As shown in Table 1, the increase of the electron concentration was remarkable as compared with the decrease of the carrier mobility induced by the Sb doping, and consequently the electric conductivity increased.

FIGS. 3A and 3B are the results of measuring the electrical conductivity according to the temperature of the produced specimen.

The electrical conductivity of the n-type semiconductor is represented by the following equation (1).

[Equation 1]

Where e is the electron charge, n is the electron concentration, μ is the electron mobility, m ^* is the effective mass of the electron, and τ is the relaxation time of the electron. The electrical conductivity of the solid solution increased from 3.3 × 10 ² S / m to 4.5 × 10 ⁴ S / m by Sb doping because of the increase of the carrier concentration. In Sb-free samples, the electrical conductivity increased rapidly with increasing temperature and showed non-degenerate semiconducting properties. The electrical conductivity decreased with increasing Ge content. Sb doped specimens exhibited degenerate semiconductor properties regardless of temperature.

As shown in Table 1, the electrical conduction type changes according to the Ge content because bipolar conduction occurs. This results in different carrier concentration and mobility depending on the composition of Mg ₂ Si _1-x Ge _x . The majority carriers of Mg ₂ Si are electrons whereas the majority carriers of Mg ₂ Ge are holes. In the case of Sb doped specimens, the electrical conductivity increased at a certain temperature. This is because the carrier concentration is increased compared to the specimen in which Sb is not doped.

FIGS. 4A and 4B are the results of measuring the Seebeck coefficient according to the temperature of the produced specimen. Referring to FIG. 4A, the following will be described. The Seebeck coefficient changed from -513 ㎶ / K to 51 ㎶ / K as Ge content increased at room temperature. The sign of the Seebeck coefficient coincides with the Hall coefficient of Table 1. This means that as the Ge content increases, the number of carriers contributing to electrical conduction is changed from n-type conduction to p-type conduction. As a result, the Mg ₂ Si _1-x Ge _x solid solution is a thermoelectric material that is extremely sensitive to the element composition. | α | = r - c ln n (| α |: Absolute value of the Seebeck coefficient, r: scattering parameter, c: constant, n: carrier concentration) As the thermal activation is increased by the dopant and the temperature, n is increased, and |? | is decreased. In all samples where Sb was not doped, as the temperature increased, | α | decreased and saturation was observed. In the case of x ≥ 0.7, p-type conductivity is exhibited at room temperature, but it is converted to n-type conductivity at high temperature. This is due to bipolar conduction by the addition of Ge. All Sb-doped specimens showed n-type conduction (negative Seebeck coefficient), which means that the Sb atoms worked successfully as electron donors in Mg ₂ Si _1-x Ge _x . The Sb-doped specimens showed a -131 ㎶ / K to -259 ㎶ / K and | a | increased with increasing temperature and Ge content.

The anti-coercive force? of the n-type semiconductor is represented by the following equation (2).

&Quot; (2) &quot;

Where k is Boltzmann's constant, r is the power function exponent (the exponent of the power function in the energy-dependent relaxation time expression), E _C is the conduction band bottom (bottom of the conduction band), E _F is the Fermi energy, T is Where n is the charge carrier concentration, γ is the scattering factor, and c is a constant. As shown in FIG. 4B, the absolute value of the anti-Seebeck coefficient (| 留 |) of intrinsic Mg ₂ Si _0.5 Ge _0.5 was very high at low temperature (-513 ㎶ / K at 323 K). However, as the temperature increased, it tended to decrease significantly (-151 ㎶ / K at 823 K). This is due to the increase in electron concentration due to intrinsic conduction. As described above, the Boehb coefficient is negatively coincident with the Hall coefficient of Table 1. As the doping amount of Sb increases, the absolute value of the deflecting coefficient (| α |) decreases due to the increase of carrier concentration. The | α | of Sb doped Mg ₂ Si _0.5 Ge _0.5 increased as the temperature increased and decreased above a certain temperature. This is due to the increase in electron concentration due to intrinsic conduction, and the increase in electron concentration at high temperature is remarkable compared to electron-phonon scattering. The Seebeck coefficient of Sb doped specimens was -199 ㎶ / K ~ -112 ㎶ / K at 323 K and -256 ㎶ / K ~ -222 ㎶ / K at 823 K.

5A to 5C are measurement results of the thermal conductivity of the prepared specimen according to the temperature. Referring to FIG. 5A, the following will be described. For the specimens without doping with Sb, the thermal conductivity decreased with increasing temperature, and the thermal conductivity increased with intrinsic conduction above 723K. The Mg ₂ Si _1-x Ge _x solid solution exhibits low thermal conductivity because of the typical alloying effect in which the solute atoms (Si or Ge) serve as the center of phonon scattering and thermal conductivity decreases. However, the thermal conductivity of the solid solution increased slightly with increasing temperature. It is considered that this is due to the increase of the electronic thermal conductivity due to the increase of the carrier concentration due to the high conduction. Of the specimens not doped with Sb, Mg ₂ Si _0.7 Ge _0.3 And showed the lowest thermal conductivity at a certain temperature. Sb doping further reduced thermal conductivity above 723 K due to scattering of dopants (ionized impurities) by Sb atoms. 5B and 5C, the following will be described. The thermal conductivity (κ) is the sum of the lattice thermal conductivity (κ _L ) by phonon and the electronic thermal conductivity (κ _E ) by the carrier. The two components can be separated by the Biedemann-Franz law (κ _E = LσT). Here, the Lorentz number is assumed to be a constant for evaluation (L = 2.45 x 10 ^-8 V ² K ^-2 ). In all specimens, the thermal conductivity decreased with increasing temperature. In addition, the thermal conductivity increased by bipolar conduction induced by intrinsic excitation at over 623K in specimens not doped with Sb and over 723K in specimens doped with Sb. In the case of Sb doped specimens, it is believed that this is due to the increase in electronic thermal conductivity due to the increase in carrier concentration due to high conduction. As a result, the intrinsic conduction temperature of the Sb doped specimen was higher than that of the undoped Sb specimen. Compared to intrinsic Mg ₂ Si _0.5 Ge _0.5 , Sb doping results in slightly increased thermal conductivity because of the higher electronic contribution. However, the thermal conductivity of Sb doped specimens at 723 K and above was lower than that of intrinsic Mg ₂ Si _0.5 Ge _0.5 due to lower grating contribution. The lowest thermal conductivity was 2.3 W / mK (Mg ₂ Si _0.5 Ge _0.5 Sb _0.02 , 723K).

Figures 6A and 6C show the dimensionless figure of merit (ZT) with temperature for the prepared specimens. As an index related to the energy conversion efficiency of the thermoelectric material, the ZT value was determined by the following equation (3).

&Quot; (3) &quot;

Where m _e is the electronic mass. Thus, an excellent thermoelectric material must have a high shear coefficient (large effective mass of the carrier), high electrical conductivity (low carrier scattering) and low thermal conductivity (high phonon scattering).

Referring to FIG. 6A, the following will be described. The ZT values of the specimens not doped with Sb were very low at less than 0.05 at all the temperatures analyzed. However, the ZT value of the specimen doped with Sb in Mg ₂ Si _1-x Ge _x solid solution was remarkably increased, and the thermal conductivity decreased due to the formation of solid solution of Mg ₂ Si and Mg ₂ Ge. . Also, since the electrical conductivity and the Seebeck coefficient are controlled by Sb doping for optimizing the carrier concentration, the thermoelectric performance will be further improved according to the present invention. As shown in FIG. 6A, the specimen Mg ₂ Si _0.7 Ge _0.3 : Sb _0.02 prepared according to one embodiment of the present invention At 823K, ZT = 0.50, Mg ₂ Si _0.5 Ge _0.5 : Sb _0.02 ZT = 0.56, Mg ₂ Si _0.3 Ge _0.7 : Sb _0.02 at 823K At 823K ZT = 0.32.

Referring to FIG. 6B, the following will be described. ZT values of the specimens not doped with Sb were very low, less than 0.05. This is due to the low carrier concentration (low electrical conductivity). However, when Sb was doped, the electrical properties were remarkably improved, the high shear coefficient was obtained, and the low thermal conductivity at high temperature was shown. As a result, the ZT value increased remarkably with Sb doping and the maximum value was 0.56 (Mg ₂ Si _0.5 Ge _0.5 Sb _0.02 , 823K).

Claims (15)

(Step a) of a raw material powder containing Mg powder, Si powder, Ge powder and Sb powder;
A solid phase reaction step (step b) in which the powder mixed in step a) is heat treated in a temperature range of 773 to 973K to react in a solid state; And
And a step (c) of hot compressing the powder synthesized in the step (b).
The method according to claim 1,
Wherein the step (a) is performed according to a stoichiometric composition of Mg ₂ Si _1-x Ge _x Sb _m (0 <x <1, 0 < _m ≦ 0.1).
The method according to claim 1,
Wherein said step (a) is performed according to a stoichiometric composition of Mg ₂ Si _1-x Ge _x Sb _m (0.3 ≦ _x ≦ 0.7, 0.005 ≦ _m ≦ 0.03).
delete The method according to claim 1,
Wherein the step (b) is performed for 1 to 10 hours.
The method according to claim 1,
Wherein the step (c) is performed at a pressure of 10 to 100 MPa and a temperature range of 973 to 1173K.
The method according to claim 1,
Wherein the mixed raw material powder is cold-pressed before performing the solid-phase reaction step.
The method of claim 7,
Wherein the cold compression process is performed at a pressure of 10 to 1000 MPa.
delete delete delete delete delete delete delete

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