KR20220068079A - Off-stoichoimetric tetrahedrite-based thermoelectric materials and method for preparing the same - Google Patents

Abstract

A thermoelectric material according to various embodiments of the present invention comprises a tetrahedrite-based compound represented by chemical formula 1. The chemical formula 1 is represented by: Cu_(12+m)Sb_(4+x)S_(13+y) where -1.0 <= m <= 1.0, -1.0 <= x <= 1.0, -1.0 <= y <= 1.0, and composition with m, x and y equal to zero all at once is excluded. A method for manufacturing the thermoelectric material according to various embodiments of the present invention comprises the steps of: weighing and preparing a raw material to fit to a composition formula being Cu_(12+m)Sb_(4+x)S_(13+y) where -1.0 <= m <= 1.0, -1.0 <= x <= 1.0, -1.0 <= y <= 1.0, and composition with m, x and y equal to zero all at once is excluded; synthesizing powder by alloying the prepared raw material mechanically; and performing the hot pressing (HP) of the powder. Therefore, provided are a thermoelectric material and a manufacturing method thereof, wherein thermoelectric performance is improved by maximizing an output factor.

Description

Non-stoichiometric tetrahedrite-based thermoelectric materials and method for preparing the same

The present invention relates to a tetrahedrite-based thermoelectric material and a method for manufacturing the same, and more particularly, to a tetrahedrite-based thermoelectric material having a non-stoichiometric composition and a method for manufacturing the same.

Thermoelectric conversion technology that can directly convert thermal energy and electric energy is emerging as a promising eco-friendly energy system. Thermoelectric materials have different temperature ranges that show maximum performance, and it is known that Bi-Te-based materials in the room temperature range, Pb-Te-based, skutterudite-based materials in the medium temperature range, and Si-Ge-based materials in the high temperature range are known to be excellent. . However, there is a problem that most of them consist of toxic heavy metals or rare elements with limited reserves. Accordingly, a tetrahedrite compound composed of Cu and S, which has abundant reserves, is inexpensive, and is relatively light and nontoxic, is attracting attention as a promising p-type thermoelectric material in the mesophilic region. The main reason why tetrahedrite is attracting attention is because it shows low thermal conductivity and has high energy band degeneracy due to its symmetrical crystal structure, so it is useful for improving the output factor.

To obtain a high ZT according to the thermoelectric figure of merit relation, ZT = α ² σκ ^-1 T (α: Seebeck coefficient, σ: electrical conductivity, κ: thermal conductivity, T: absolute temperature), high Seebeck coefficient, electrical conductivity, and low thermal conductivity should have the Since the Seebeck coefficient and electrical conductivity have a trade-off relationship with respect to the output factor, the output factor is generally improved by optimizing the carrier concentration through doping. Research on tetrahedrite to maximize output factor and reduce thermal conductivity by controlling carrier (hole) concentration by substituting various transition elements for Cu sites is in progress.

However, there are few studies on the non-stoichiometric composition to manipulate the content of Cu sites in tetrahedrites.

The present invention relates to a tetrahedrite having a non-stoichiometric composition with a controlled Cu content, and an object of the present invention is to provide a thermoelectric material with improved thermoelectric performance by maximizing an output factor, and a method for manufacturing the same.

The thermoelectric material according to various embodiments of the present invention includes a tetrahedrite-based compound represented by Formula 1 below.

[Formula 1]

Cu _12+m Sb _4+x S _13+y

where -1.0 ≤ m ≤1.0, -1.0 ≤ x ≤1.0, -1.0 ≤ y ≤ 1.0,

Compositions in which m, x, and y are simultaneously 0 are excluded.

In the method of manufacturing a thermoelectric material according to various embodiments of the present invention, the raw material is prepared by the composition formula Cu _{12 + m} Sb _{4 + x} S _{13 +y} (here, -1.0 ≤ m ≤1.0, -1.0 ≤ x ≤1.0, -1.0 ≤ y ≤ 1.0, and m, x, and y at the same time exclude compositions of 0) by weighing and preparing; synthesizing powder by mechanically alloying the prepared raw material; and hot pressing (HP) the powder.

Various embodiments of the present invention may provide a thermoelectric material with improved thermoelectric performance and a method for manufacturing the same.

The tetrahedrite-based thermoelectric material of the present invention can improve the thermoelectric figure of merit by maximizing the output factor. According to an embodiment of the present invention, Cu _{11 .} In the case of ₉ Sb ₄ S ₁₃ , a maximum ZT = 0.91 was obtained at 723 K, which was superior to ZT = 0.86 of Cu ₁₂ Sb ₄ S ₁₃ , a stoichiometric tetrahedrite.

The manufacturing method of the present invention can prevent volatilization of elemental components and segregation of dopants that may occur in the dissolution process for the conventional tetrahedrite-based compound production by using mechanical alloying and hot compression molding, and a homogeneous tetrahedrite phase can be synthesized. In addition, it is very suitable for mass production by lowering the manufacturing cost and remarkably reducing the process time to increase the process efficiency compared to the dissolution method in which a high temperature must be maintained for a long time. In addition, it is an effective process because it can produce homogeneous Cu _{12 + m} Sb _{4 + x} S _{13 + y} through solid-state synthesis within a relatively short time.

1 shows the X-ray diffraction pattern of Example 1.
2 shows the lattice constant of Example 1. FIG.
3 is an SEM photograph of the fracture surface of Example 1. FIG.
4 is a graph of electrical conductivity of Example 1.
5 is a graph of the Seebeck coefficient of Example 1.
6 shows an output factor (PF = α ² σ ) of Example 1.
7 shows the thermal conductivity of Example 1.
8 shows the Lorenz number of Example 1.
9 is a graph in which electron thermal conductivity and lattice thermal conductivity of Example 1 are separated.
10 shows the dimensionless thermoelectric figure of merit ( ZT ) of Example 1.

Hereinafter, various embodiments of the present document will be described with reference to the accompanying drawings. The examples and terms used therein are not intended to limit the technology described in this document to a specific embodiment, but it should be understood to cover various modifications, equivalents, and/or substitutions of the embodiments.

The thermoelectric material according to various embodiments of the present invention is represented by the following formula (1).

[Formula 1]

Cu _12+m Sb _4+x S _13+y

where -1.0 ≤ m ≤1.0, -1.0 ≤ x ≤1.0, -1.0 ≤ y ≤ 1.0,

Compositions in which m, x, and y are simultaneously 0 are excluded.

More specifically, the thermoelectric material according to various embodiments of the present invention is represented by the following formula (1).

[Formula 1]

Cu _12+m Sb ₄ S ₁₃

Here, -0.3 ≤ m < 0, 0 < m ≤ 0.3.

Preferably, m may be -0.3, -0.2, -0.1, 0.1, 0.2 or 0.3.

The thermoelectric material according to various embodiments of the present invention is a tetrahedrite-based compound having a non-stoichiometric composition, and may provide a thermoelectric material with improved thermoelectric performance by reducing thermal conductivity and optimizing an output factor.

A method of manufacturing a thermoelectric material according to various embodiments of the present disclosure includes preparing a raw material; synthesizing powder by mechanically alloying the prepared raw material; and hot pressing (HP) the powder.

In the step of preparing the raw material, the raw material has a compositional formula Cu _{12 + m} Sb _{4 + x} S _{13 +y} (here, -1.0 ≤ m ≤1.0, -1.0 ≤ x ≤1.0, -1.0 ≤ y ≤ 1.0, m , x, and y at the same time are excluded from the composition.) It can be prepared by weighing it accordingly. At this time, Cu may prepare an elemental powder having a particle size of less than 45 μm, Sb may prepare an elemental powder having a particle size of less than 150 μm, and S may prepare an elemental powder having a particle size of less than 75 μm.

Next, in the step of synthesizing the powder, the prepared raw material may be mechanically alloyed (MA). The prepared mixed powder and a steel ball having a diameter of 4 to 6 mm can be mixed in a ratio of 1:15 to 1:20 for ball milling. Specifically, it may be ball milled at 200 rpm to 2000 rpm for 1 hour to 100 hours. If the ball milling speed is less than 200 rpm, the Cu _{12 + m} Sb _{4 + x} S _{13 +y} phase may not be properly synthesized, and if the ball milling speed is greater than 2000 rpm, phase decomposition or secondary phase may be formed due to excessive energy. . On the other hand, if the ball milling time is shorter than 1 hour, the Cu _12+m Sb _4+x S _13+y phase may not be properly synthesized, and if it is longer than 100 hours, phase decomposition or secondary phase may be formed due to excessive energy. can Preferably, it can be ball milled at 350 rpm for 22 hours to 26 hours.

Next, the hot compression molding is preferably performed in a temperature range of 473 K to 873 K and a pressure range of normal pressure to 100 MPa. At a condition lower than this range, a desired sintering result may not be obtained, and at a condition higher than this range, the manufacturing cost may increase. On the other hand, preferably, in the case of sintering by hot pressing (HP), it may be sintered at a pressure of 70 Mpa in a temperature range of 523 K to 623 K. More preferably, it may be sintered at a temperature of 573 K and a pressure of 70 Mpa.

The manufacturing method of the present invention can prevent volatilization of elemental components and segregation of dopants that may occur in the dissolution process for the conventional tetrahedrite-based compound production by using mechanical alloying and hot compression molding, and a homogeneous tetrahedrite phase can be synthesized. In addition, it is very suitable for mass production by lowering the manufacturing cost and remarkably reducing the process time to increase the process efficiency compared to the dissolution method in which a high temperature must be maintained for a long time. In addition, it is an effective process because it can produce homogeneous Cu _{12 + m} Sb _{4 + x} S _{13 + y} through solid-state synthesis within a relatively short time.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Example 1: Tetrahedrite Cu of Non-Stoichiometric Composition _12+m Sb ₄ S ₁₃

Mechanical alloying (MA) of tetrahedrite Cu _{12 + m} Sb ₄ S ₁₃ (-0.3, -0.2, -0.1, 0, 0.1, 0.2, and 0.3) of non-stoichiometric composition by controlling the stoichiometric composition and content of Cu ) method was synthesized. Weigh Cu (purity 99.9%, < 45 ㎛, Kojundo), Sb (purity 99.999%, < 150 ㎛, Kojundo), S (purity 99.99%, < 75 ㎛, Kojundo) powder according to the composition, 5mm in diameter) was charged into a hardened steel jar with a weight ratio (BPR) of 20. Mechanical alloying (MA) was performed in an Ar atmosphere for 24 hours at a rotation speed of 350 rpm with a planetary mill (Fritsch Pulverisette 5). For sintering, the synthesized tetrahedrite powder was charged into a graphite mold having an inner diameter of 10 mm, and vacuum hot compression molding (HP) was performed at 723 K for 2 hours at a pressure of 70 MPa. The Seebeck coefficient and electrical conductivity of the sintered body were measured by cutting 3 mm Х 3 mm Х 9 mm in the shape of a cuboid, and thermal conductivity measurements were performed by cutting in the shape of a disk of 10 mm (diameter) Х 1 mm (thickness).

[Experimental example]

Experimental method

For the phase analysis of the HP sintered body, Cu Kα radiation (λ = 0.15405 nm) was used as an X-ray diffraction analyzer (XRD; Bruker D8-Advance). The diffraction pattern was measured in θ-2θ mode (2θ = 10-90°) with a step size of 0.02° and a scan speed of 0.4 sec/step. In order to observe the microstructure of the sintered body, the fracture surface of the HP specimen was observed with a scanning electron microscope (SEM; FEI Quanta400). Measurements were carried out in the temperature range of 323-723 K, and Seebeck coefficient and electrical conductivity were measured using the temperature differential method and DC 4-terminal method in He atmosphere, respectively (Ulvac-Riko ZEM-3), and thermal conductivity was measured for thermal diffusivity and specific heat. And the density was measured by the laser flash method (Ulvac-Riko TC-9000H). The output factor and the dimensionless figure of merit were evaluated using the finally obtained values.

Experimental Example 1: X-ray diffraction pattern analysis of Example 1

1 shows the XRD pattern of Cu _{12 + m} Sb ₄ S ₁₃ (-0.3 ≤ m ≤ 0.3) after sintering in Example 1.

)와 잘 일치하여 테트라헤드라이트 상이 성공적으로 합성되었음을 확인하였다. 또한 비화학양론에 의한 이차상은 발견되지 않았다. 그러나 Cu의 함량 변화(m)에 따라 회절피크의 각도가 변하여 격자의 수축 또는 팽창이 예측되었다. 도 2와 같이 Cu 함량이 결핍에서 과잉으로 갈수록 즉 m = -0.3 에서 m = 0.3 으로 증가할수록 격자상수가 1.0338 에서 1.0384 nm 로 증가하였다. 화학양론 시편 (m = 0)의 격자상수는 1.0350 nm 이었기 때문에, Cu-poor 시편은 격자가 수축되고, Cu-rich 시편은 격자가 팽창되었음을 의미한다. ICDD standard diffraction data of tetrahedrite (PDF#024-1318, space group)

), confirming that the tetrahedrite phase was successfully synthesized. In addition, non-stoichiometric secondary phases were not found. However, as the angle of the diffraction peak changed according to the change in the Cu content (m), the shrinkage or expansion of the grating was predicted. As shown in FIG. 2, the lattice constant increased from 1.0338 to 1.0384 nm as the Cu content increased from deficiency to excess, that is, from m = -0.3 to m = 0.3. Since the lattice constant of the stoichiometric specimen (m = 0) was 1.0350 nm, Cu-poor specimens contracted the lattice and Cu-rich specimens expanded the lattice.

Experimental Example 2: Analysis of the shape and composition of Example 1

3 is sintered Cu _{12 + m} Sb ₄ S ₁₃ psalm This is an SEM picture of the fracture surface. The theoretical density of tetrahedrite was 4.99 gcm ^-3 , and the sample sintered by hot pressing obtained a dense relative density of 99.0-100.0%. No specific change in microstructure according to Cu content was found. As with the XRD analysis results, no unreacted residual elements or secondary phases due to phase separation were observed.

Experimental Example 3: Seebeck coefficient analysis of Example 1

4 is a graph showing the temperature dependence of the electrical conductivity of Cu _{12 + m} Sb ₄ S ₁₃ . In the case of Cu-rich specimens in the 323-723 K temperature range, the non-degenerate semiconductor behavior was increased as the temperature increased. However, in the case of the Cu-poor specimen, the temperature dependence was not large, and the degenerate semiconductor behavior was shown above 623 K. Compared with the stoichiometric specimen, the electrical conductivity of the Cu-rich specimen at a constant temperature decreased, but the electrical conductivity increased in the case of the Cu-poor specimen. That is, as m decreased, the electrical conductivity increased. As a result, Cu _{11 . 7} Sb ₄ S ₁₃ showed the highest electrical conductivity of 4.5Х10 ⁴ Sm ^-1 at a temperature of 623 K. Although there is no report on the effect of deficient Cu content on the electrical properties of tetrahedrite, for firming geartite Cu _{3 - x} SbSe ₄ (x = 0-0.075), the carrier (hole) concentration increased as the content of Cu was deficient. There are research data showing that the electrical resistivity is greatly reduced by Therefore, when compared with the stoichiometric Cu ₁₂ Sb ₄ S ₁₃ , when the Cu content is excessive, the carrier concentration is lowered, and conversely, when the Cu content is insufficient, it is judged to contribute to increasing the carrier concentration.

Experimental Example 4: Seebeck coefficient analysis of Example 1

(k_B: Boltzmann constant, m^*: effective carrier mass, e : electronic charge, h: Planck constant, and n: carrier concentration)로 표현된다. 온도가 증가하면 제벡 계수 값이 증가하다가 특정 온도 이상에서 진성천이에 의해 캐리어 농도가 급격히 증가하여 제벡계수가 감소한다. 본 실험예에서 모든 시편이 측정온도 범위에서 진성천이가 발생하지 않았다. 화학양론 조성에 도펀트 원소를 치환한 다른 연구들과 같이 캐리어 농도의 변화가 크지 않아 본 연구에서 723 K까지 진성천이가 발생하지 않았다. 때문에 Cu_{12 + m}Sb₄S₁₃ (-0.3 ≤ m ≤ 0.3) 의 진성천이 온도가 723 K 이상일 것으로 예상된다. 그러나, m이 증가할수록 고온에서의 온도 의존성이 둔화된 것으로 보아, Cu 함량의 과잉은 진성천이 온도를 낮추는데 기여한다고 판단된다. 반대로 Cu 함량의 결핍은 캐리어 농도를 증가시켜 제벡계수는 감소시키지만, 진성천이 온도는 상향시키는데 기여할 수 있다. 일정온도에서 Cu 함량이 증가할수록 제벡계수가 증가하여, Cu_{12 . 3}Sb₄S₁₃ 가 723 K 에서 208 μVK^{- 1} 의 최대 제벡계수를 나타내었다. 이것은 Cu₁₂Sb₄S₁₃의 723 K 에서 최대 제벡계수 183 μVK^-1 보다 큰 값이다. 5 shows the temperature dependence of the Seebeck coefficient of the Cu _{12 + m} Sb ₄ S ₁₃ sample. All specimens showed positive values as seen in p-type semiconductors. The Seebeck coefficient of the P-type semiconductor is

(k _B : Boltzmann constant, m ^* : effective carrier mass, e: electronic charge, h: Planck constant, and n: carrier concentration). As the temperature increases, the Seebeck coefficient value increases, but above a certain temperature, the carrier concentration rapidly increases due to intrinsic transition, and the Seebeck coefficient decreases. In this experimental example, no intrinsic transition occurred in any of the specimens in the measurement temperature range. As in other studies in which the dopant element was substituted for the stoichiometric composition, the change in carrier concentration was not large, so intrinsic transition did not occur up to 723 K in this study. Therefore, the intrinsic transition temperature of Cu _{12 + m} Sb ₄ S ₁₃ (-0.3 ≤ m ≤ 0.3) is expected to be 723 K or higher. However, as m increases, the temperature dependence at high temperature appears to be weakened, and it is judged that an excess of Cu content contributes to lowering the intrinsic transition temperature. Conversely, a lack of Cu content increases the carrier concentration and decreases the Seebeck coefficient, but may contribute to raising the intrinsic transition temperature. As the Cu content increases at a constant temperature, the Seebeck coefficient increases, Cu _{12 . 3} Sb ₄ S ₁₃ exhibited a maximum Seebeck coefficient of 208 μVK ^{- 1} at 723 K. This is larger than the maximum Seebeck coefficient of 183 μVK ^-1 at 723 K of Cu ₁₂ Sb ₄ S ₁₃ .

Experimental Example 5: Analysis of the output factor of Example 1

) 제벡계수는 캐리어 농도에 반비례하고, 전기전도도는 캐리어 농도에 비례하기 때문에 출력인자는 두 인자와 trade-off 관계에 있다. Cu-poor 샘플이 Cu-rich 보다 높은 출력인자를 나타낸 것을 보아 테트라헤드라이트의 출력인자는 제벡계수의 증가보다 전기전도도의 감소의 영향이 크다. Cu₁₂Sb₄S₁₃ 시편이 723 K 에서 최대 PF = 0.95 mWm^-1K^{- 2} 이며, 비화학양론 시편의 경우, 723 K 에서 Cu_{11 . 7}Sb₄S₁₃ 과 Cu_11.9Sb₄S₁₃이 최대 1.08 mWm^-1K^{- 2} 를, Cu_{12 . 3}Sb₄S₁₃ 이 최소 0.66 mWm^-1K^{- 2} 를 나타내었다. 따라서 테트라헤드라이트의 Cu 의 결핍이 캐리어농도를 증가시켜 화학양론 Cu₁₂Sb₄S₁₃ 보다 높은 출력인자를 얻을 수 있다. 6 is a graph showing an output factor of Cu _{12 + m} Sb ₄ S ₁₃ . As the temperature increased, the output factor increased. The output factor increases in proportion to the Seebeck coefficient and electrical conductivity. (PF =

) Since the Seebeck coefficient is inversely proportional to the carrier concentration and the electrical conductivity is proportional to the carrier concentration, the output factor has a trade-off relationship with the two factors. As the Cu-poor sample showed a higher output factor than that of Cu-rich, the output factor of tetrahedrite had a greater effect on the decrease in electrical conductivity than the increase in the Seebeck coefficient. The Cu ₁₂ Sb ₄ S ₁₃ specimen had a maximum PF = 0.95 mWm ^-1 K ^-2 at 723 K, and for the non ^- stoichiometric specimen, Cu ₁₁ at 723 _{K. 7} Sb ₄ S ₁₃ and Cu _11.9 Sb ₄ S ₁₃ up to 1.08 mWm ^-1 K ^{- 2} , Cu _{12 . 3} Sb ₄ S ₁₃ showed a minimum of 0.66 ^{mWm -1} K ^-2 . Therefore, the lack of Cu in tetrahedrite increases the carrier concentration, so that an output factor higher than the stoichiometric Cu ₁₂ Sb ₄ S ₁₃ can be obtained.

Experimental Example 6: Thermal conductivity analysis of Example 1

7 is a graph showing the thermal conductivity of Cu _{12 + m} Sb ₄ S ₁₃ . There was almost no temperature dependence on the thermal conductivity of all specimens. As the Cu content increased, the thermal conductivity decreased from 0.98 to 0.57 Wm ^-1 K ^-1 at 323 K ^and from 0.97 ^to 0.66 Wm ^-1 K ^-1 at 723 K. Therefore, Cu-rich tetrahedrite exhibits very low thermal conductivity based on the stoichiometric Cu ₁₂ Sb ₄ S ₁₃ (0.72-0.77 Wm ^-1 K ^-1 at 323-723 K).

식을 사용하여 구하여 도 8에 나타내었다. Lorenz number는 이론적으로 (1.45-2.44)×10^-8 V²K^-2 의 범위를 가지며, 값이 작을수록 비축퇴 반도체(값이 클수록 축퇴반도체 또는 금속성) 거동을 의미한다. Cu 함량이 감소할수록 캐리어 농도 증가(제벡계수의 감소)로 Lorenz number 가 323 K 의 1.70×10^-8 에서 1.89×10^-8 V²K^{- 2}으로 723 K 의 1.65×10^-8 에서 1.76×10^-8 V²K^{- 2} 로 증가하였다. 따라서 도 4의 전기전도도 온도의존성과 같이, Cu 함량이 감소할수록 비축퇴 반도체에서 축퇴 반도체로 전이될 가능성이 크다.Thermal conductivity is the sum of electronic thermal conductivity (κ _E ) and lattice thermal conductivity (κ _L ), and electronic thermal conductivity was calculated according to the Wiedemann-Franz law (κ _E = LσT, L: Lorenz number). In this experimental example, the Lorenz number is

It was obtained using the formula and is shown in FIG. 8 . Lorenz number theoretically has a range of (1.45-2.44)×10 ^-8 V ² K ^-2 , and the smaller the value, the more the behavior of the non-degenerate semiconductor (the larger the value, the more degenerate semiconductor or metallic). As the Cu content decreases, the carrier concentration increases (reduction of the Seebeck coefficient) and the Lorenz number changes from 1.70×10 ^-8 to 1.89×10 ^-8 V ² K ^{- 2} at 323 K, and 1.65×10 ^-8 to 1.76×10 at 723 K ^-8 V ² K ^{- 2} increased. Therefore, as with the temperature dependence of electrical conductivity of FIG. 4 , as the Cu content decreases, the possibility of transition from the non-degenerate semiconductor to the degenerate semiconductor is high.

9 shows the separation of electronic thermal conductivity and lattice thermal conductivity on thermal conductivity. As shown in Fig. 9(a), as the temperature increased, the electronic thermal conductivity increased, which is because carrier heat transfer increased due to an increase in carrier concentration. As the Cu content increased at a constant temperature, the electrical conductivity decreased (carrier concentration decreased), so that the Cu-rich sample showed lower electronic thermal conductivity than that of the Cu-poor. Cu _{12 .} The ₃ Sb ₄ S ₁₃ sample showed the lowest electronic thermal conductivity of 0.04-0.17 Wm ^-1 K ^{-1 in} the temperature range of 323-723 K. As shown in Fig. 9(b), in the case of the Cu-poor specimen, the lattice thermal conductivity decreased as the temperature increased (at least 0.40 Wm ^-1 K ^-1 at 723 K), which is a result of reduced heat transfer due to phonon scattering. However, the Cu ^- rich sample showed little temperature dependence with 0.45-0.52 Wm ^-1 K ^-1 in the temperature range of 323-723 K. Compared with the thermal conductivity of FIG. 7 , it can be seen that heat transfer by phonons is dominant at low temperatures, and the contribution of heat transfer by carriers increases at high temperatures. Tetrahedrites inherently lead to low thermal conductivity, and excess Cu atoms further lower the lattice thermal conductivity through phonon scattering, bringing the lattice thermal conductivity closer to the theoretical minimum.

Experimental Example 7: Thermoelectric figure of merit (ZT) analysis of Example 1

10 shows the dimensionless thermoelectric figure of merit (ZT) of Cu _{12 + m} Sb ₄ S ₁₃ . As the temperature increased, the ZT increased. This is because the output factor increased and the thermal conductivity was kept low until the intrinsic transition temperature. The ZT range was 0.13-0.20 at 323 K and 0.71-0.91 at 723 K. Cu ₁₁ deficient in Cu content _{. 9} Sb ₄ S ₁₃ showed high ZT over the entire temperature range, and the highest figure of merit of 0.91 was obtained at 723 K. This is higher than ZT = 0.86 at 723 K of the stoichiometric Cu ₁₂ Sb ₄ S ₁₃ . Therefore, it can be seen that deficient Cu content of tetrahedrite is helpful in improving the thermoelectric performance by optimizing the carrier concentration and maximizing the output factor. As a result, in this example, it was confirmed that a non-stoichiometric tetrahedrite single phase could be synthesized in a solid phase by the MA-HP process, and excellent thermoelectric performance was exhibited when the Cu content was deficient rather than the excess Cu in the non-stoichiometric composition.

Features, structures, effects, etc. described in the above-described embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to one embodiment. Furthermore, the features, structures, effects, etc. illustrated in each embodiment can be combined or modified for other embodiments by those of ordinary skill in the art to which the embodiments belong. Accordingly, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

In addition, although the embodiments have been described above, these are merely examples and do not limit the present invention, and those of ordinary skill in the art to which the present invention pertains are exemplified above in a range that does not depart from the essential characteristics of the present embodiment. It can be seen that various modifications and applications that have not been made are possible. For example, each component specifically shown in the embodiments may be implemented by modification. And differences related to these modifications and applications should be construed as being included in the scope of the present invention defined in the appended claims.

Claims (7)

A thermoelectric material comprising a tetrahedrite-based compound represented by the following formula (1).
[Formula 1]
Cu _12+m Sb _4+x S _13+y
where -1.0 ≤ m ≤1.0, -1.0 ≤ x ≤1.0, -1.0 ≤ y ≤ 1.0,
Compositions in which m, x, and y are simultaneously 0 are excluded. The method of claim 1,
Formula 1 is,
Cu _12+m Sb ₄ S ₁₃ and
Here, -0.3 ≤ m < 0, 0 < m ≤ 0.3. The raw material has the composition formula Cu _{12 + m} Sb _{4 + x} S _{13 +y} (where -1.0 ≤ m ≤1.0, -1.0 ≤ x ≤1.0, -1.0 ≤ y ≤ 1.0, and m, x, and y are 0 at the same time Phosphorus composition is excluded) and preparing by weighing;
synthesizing powder by mechanically alloying the prepared raw material; and
A method of manufacturing a thermoelectric material comprising the step of hot pressing the powder (Hot Pressing, HP). 4. The method of claim 3,
In the step of synthesizing the powder, the method for producing a thermoelectric material, characterized in that the prepared raw material is performed under the conditions of 200 rpm to 2000 rpm. 4. The method of claim 3,
In the step of synthesizing the powder, the method for producing a thermoelectric material, characterized in that ball milling the prepared raw material for 1 hour to 100 hours. 4. The method of claim 3,
The step of hot compression molding is a method of manufacturing a thermoelectric material, characterized in that it is performed in a temperature range of 473 K to 873 K. 4. The method of claim 3,
The method of manufacturing a thermoelectric material, characterized in that the hot compression molding is performed in a pressure range of normal pressure to 100 MPa.

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