Thermoelectric material and method for forming the same

Abstract

Provided are thermoelectric materials and a method for forming the same. 【Solution means】The thermoelectric material has the following Chemical Formula 1. [Chemical Formula 1] [(Bi2) m (Bi2Ch3) n (1-y) / l [A2Q x y (In the Chemical Formula 1, Ch = Te or Se, A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6, 0 ≤ y ≤ 0.4) The method for forming the thermoelectric material includes steps of sealing reactants including Bi, Te, Se, and A2Q x (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6), heating and melting the reactants to cause a reaction, cooling the result of the reaction to form an ingot, and pulverizing the ingot into powder and then sintering the powder.​​

Description

[Technical Field]

[0001] The present invention relates to thermoelectric materials and methods for forming them. [Background technology]

[0002] Thermoelectric phenomena include the transfer of heat through the flow of electrons and holes within thermoelectric materials, and the movement of electrons and holes induced by heat transfer. This can be applied to a variety of industrial fields, such as cooling applications based on the Peltier effect, which generates a temperature difference across a material when an electric current is applied, and power generation applications utilizing the Seebeck effect, which generates an electromotive force internally when a temperature gradient exists within a material.

[0003] The power generation and cooling performance of thermoelectric materials is determined by the thermoelectric conversion efficiency of the p-type and n-type semiconductor materials that constitute the element. Thermoelectric conversion efficiency is expressed by the dimensionless thermoelectric figure of merit (ZT=σS), which is the relationship between electrical conductivity (σ), thermal conductivity (κ), Seebeck coefficient (S), and absolute temperature (T). 2 It is determined by T / κ. The performance index is limited in its ability to be improved due to the strong interrelationships between the constituent variables. [Overview of the project] [Problems that the invention aims to solve]

[0004] This invention provides a thermoelectric material with excellent performance.

[0005] The present invention provides a method for forming the aforementioned thermoelectric material.

[0006] Other objectives of the present invention will become clear from the following detailed description and accompanying drawings. [Means for solving the problem]

[0007] The thermoelectric material according to the embodiment of the present invention has the following chemical formula 1. [Chemical formula 1] [(Bi2)m (Bi2Ch3) n (1-y) / l [A2Q x y (In Chemical Formula 1, Ch = Te or Se, A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6, 0 ≤ y ≤ 0.4)

[0008] The thermoelectric material has polycrystallinity. The thermoelectric material is an n-type semiconductor.

[0009] The thermoelectric material is composed of Bi, Te, Se, and A2Q x (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6) and is formed by performing a solid-phase synthesis reaction on a reactant containing the same.

[0010] The A is located at least at one of the interlayer position, interstitial position, and ionic position of the Bi-Te-based compound of the thermoelectric material.

[0011] The method for forming a thermoelectric material according to an embodiment of the present invention includes a step of sealing a reactant containing Bi, Te, Se, and A2Q x (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6), heating and melting the reactant to cause a reaction, a step of cooling the product of the reaction to form an ingot, and a step of pulverizing the ingot into powder and then sintering the powder.

[0012] The thermoelectric material has the following Chemical Formula 1. [Chemical Formula 1] [(Bi2) m (Bi2Ch3) n (1-y) / l [A2Q x y (In Chemical Formula 1, Ch = Te or Se, A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6, 0 ≤ y ≤ 0.4)

[0013] ​​​​The thermoelectric material has polycrystallinity. The thermoelectric material is an n-type semiconductor.

[0014] The reactants are heated at a temperature of 600 to 700 °C for 22 to 26 hours. The sintering is performed using a spark plasma sintering method.

Advantages of the Invention

[0015] The thermoelectric material according to an embodiment of the present invention can have excellent performance. The thermoelectric material can have excellent electrical characteristics and an improved thermoelectric performance index. The thermoelectric material can be combined with a p-type material to realize a thermoelectric module with improved power generation efficiency.

Brief Description of the Drawings

[0016] [Figure 1] The PF (power factor) and thermal conductivity of Bi2Te3-9%K2Se6, which is a thermoelectric material according to an embodiment of the present invention, are shown in comparison with Bi2Te3. [Figure 2] The PF (power factor), thermoelectric performance index (ZT), and thermal conductivity of Bi2Te3-9%K2Se6, which is a thermoelectric material according to an embodiment of the present invention, are shown in comparison with Bi2Te3. [Figure 3] The thermoelectric performance index of a thermoelectric material according to another embodiment of the present invention is shown.

Modes for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described in detail with reference to examples. The objects, features, and advantages of the present invention will be easily understood from the following examples. The present invention is not limited to the examples described herein and can also be embodied in other forms. The examples introduced here are provided to make the disclosed content thorough and complete and to fully convey the idea of the present invention to those with ordinary knowledge in the technical field to which the present invention pertains. Therefore, the present invention should not be limited by the following examples.

[0018] The thermoelectric material according to an embodiment of the present invention has the following Chemical Formula 1. [Chemical formula 1] [(Bi2) m (Bi2Ch3) n ] (1-y) / l [A2Q x ] y (In the above chemical formula 1, Ch = Te or Se, A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6, 0 ≤ y ≤ 0.4)

[0019] In the above chemical formula 1, (Bi2) m (Bi2Ch3) n This represents a homologous series compound consisting of a combination of a Bi2 bilayer and a Bi2Ch3 quintuple layer. m represents the number of Bi2 bilayers in the crystallographic unit structure of the thermoelectric material, n represents the number of Bi2Ch3 quintuple layers in the crystallographic unit structure of the thermoelectric material, and l represents the greatest common divisor that can express the composition ratio of Bi and Ch(Te,Se), which are constituent elements of the homologous series compound, as an integer.

[0020] The thermoelectric material is polycrystalline. The thermoelectric material is an n-type semiconductor.

[0021] The thermoelectric material is Bi, Te, Se, and A2Q x It is formed by carrying out a solid-phase reaction with a reactant containing (A=Li, Na, K, Rb, or Cs, Q=S, Se, or Te, x=1~6).

[0022] The A is located at at least one of the interlayer site, interstitial site, and ion site of the Bi-Te-based thermoelectric material.

[0023] The method for forming a thermoelectric material according to an embodiment of the present invention is Bi, Te, Se, and A2Q xThe process includes the steps of sealing a reaction mixture containing (A=Li, Na, K, Rb, or Cs, Q=S, Se, or Te, x=1-6), heating it to melt and react it, cooling the reaction product to form an ingot, and grinding the ingot into a powder and then sintering it.

[0024] The thermoelectric material has the above chemical formula 1.

[0025] The reactants are heated at a temperature of 600-700°C for 22-26 hours. The sintering is carried out using a discharge plasma sintering method. [Examples]

[0026] Quartz tube containing Bi, Te, Se, A2Q x A reactant containing (A=Li,Na,K,Rb,Cs; Q=S,Se,Te; x=1~6) is quantitatively measured and added according to the target composition. The tube is then sealed under high vacuum using a high-temperature torch. The sealed reactant is heated at 650°C for 24 hours to melt it, and then cooled to obtain an ingot. This ingot is pulverized into a powder, and a pellet-shaped thermoelectric material is obtained using the Spark Plasma Sintering (SPS) method.

[0027] The aforementioned thermoelectric material has the following chemical formula 1. [Chemical formula 1] [(Bi2) m (Bi2Ch3) n ] (1-y) / l [A2Q x ] y (In the above chemical formula 1, Ch = Te or Se, A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6, 0 ≤ y ≤ 0.4) The m:n:l ratios of the chemical formula 1 according to the embodiments of the present invention are as follows. These ratios were calculated based on the unit cell structure of each solid compound. (1) m:n:l=0:3:3, (2) m:n:l=1:5: 3,(3)m:n:l=2:7:3,(4)m:n:l=3:9:3,(5)m:n:l=1:2:6,(6)m:n:l=3:3:3,(7)m:n:l=2:1:3,(8)m:n:l=15:6:6,(9)m:n:l=3:0: 6

[0028] The aforementioned thermoelectric material has a composition containing excess alkali metals and chalcogen elements, and as a result, alkali metal atoms are positioned in at least one of the interlayer, void, or ionic positions of the Bi-Te compound. Furthermore, these defects induce the localization of microstructures of Bi-Te homologous compounds different from the parent compound within the thermoelectric material. For example, BiTe defects can be locally formed within the Bi2Te3 lattice.

[0029] The thermoelectric properties of the thermoelectric materials obtained in the above examples were measured. First, to measure the electrical transport properties, a pellet sample prepared by the SPS process was cut and polished to create a rectangular specimen measuring 2.5 mm × 2.5 mm × 10 mm, and its electrical conductivity and Seebeck coefficient were measured. In addition, to measure the thermal transport properties, the remaining portion of the same pellet sample was cut and polished to create a disc-shaped specimen measuring 8 mm thick and 1.5 mm high, which was then coated with graphite, and its thermal conductivity was measured.

[0030] Analysis of the thermoelectric materials obtained in the embodiments of the present invention using induced plasma atomic emission spectroscopy revealed that they have a non-stoichiometric composition, as shown in Table 1 below.

[0031] [Table 1]

[0032] The thermoelectric materials according to embodiments of the present invention introduce diverse point defects and heterogeneous structures while maintaining an overall layered structure. In particular, alkali metals are positioned in interlayer and interstitial locations while maintaining the layered structure characteristic of Bi-Te-based materials, supplying electrons as additional charge carriers and inducing modulation of the electron band structure. This minimizes the decrease in electrical conductivity due to alloying, improves the Seebeck coefficient, and maintains the overall electrical transport properties. Point defects of various forms, such as interlayer, interstitial, and ionic locations, are induced, thereby maximizing phonon scattering through the localization of heterogeneous Bi-Te-based compounds that are homologous compounds.

[0033] Figure 1 shows the power factor (PF) and thermal conductivity of Bi2Te3-9%K2Se6, a thermoelectric material according to one embodiment of the present invention, in comparison with Bi2Te3, and Figure 2 shows the thermoelectric material Bi2Te3-9%K2Se6, according to one embodiment of the present invention. 3- The power factor (PF) and thermoelectric figure of merit (ZT) thermal conductivity of 9%K2Se6 are shown in comparison to those of Bi2Te3.

[0034] Referring to Figures 1 and 2, Bi2Te3-9% K2Se6 is approximately 40 μW / cm³ at room temperature. -1 K -2 While maintaining excellent electrical transport characteristics, the thermal conductivity at 100°C is approximately 0.88 Wm². -1 K -1 It decreased to this level. In addition, Bi2Te3-9% K2Se6 showed a high thermoelectric figure of merit (ZT) of approximately 1.4 at 100°C.

[0035] Figure 3 shows the thermoelectric figure of merit of a thermoelectric material according to another embodiment of the present invention.

[0036] Referring to Figure 3, A2Q is included in thermoelectric materials. x This was demonstrated by the fact that the thermoelectric figure of merit of the thermoelectric material changes depending on the content of (Li2Se3, Na2Se3, Li2Se6, Na2Se6) and the ratio of alkali metals (Li, Na) to Se. Furthermore, the thermoelectric material according to the embodiment of the present invention exhibits a high thermoelectric figure of merit.

[0037] The specific embodiments of the present invention have been discussed above. A person with ordinary skill in the art to which the present invention pertains will understand that the present invention can be embodied in modified forms that do not depart from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in an explanatory rather than restrictive view. The scope of the present invention is shown in the claims, not in the foregoing description, and all differences within an equivalent scope should be interpreted as being included in the present invention. [Industrial applicability]

[0038] The thermoelectric material according to the embodiment of the present invention can have excellent performance. The thermoelectric material can have excellent electrical properties and an improved thermoelectric figure of merit. The thermoelectric material can be combined with a p-type material to realize a thermoelectric module with improved power generation efficiency.

Claims

1. A thermoelectric material having the following chemical formula 1. [Chemical formula 1] (Bi) ２ ) ｍ (Bi) ２ Ch ３ ) ｎ ] （１－ｙ）／ｌ [A] ２ Q ｘ ] ｙ (In the above chemical formula 1, Ch = Te or Se, A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6, 0 < y ≤ 0.4, m represents the number of Bi 2 double layers in the crystallographic unit structure of the thermoelectric material, n represents the number of Bi 2 Ch 3 quintuple layers in the crystallographic unit structure of the thermoelectric material, and is a non-zero number, and l represents the greatest common divisor that can express the composition ratio of Bi and Ch, which are constituent elements of the congeneral series compounds, as an integer.)

2. The thermoelectric material according to claim 1, characterized in that the thermoelectric material is polycrystalline.

3. The thermoelectric material according to claim 1, characterized in that the thermoelectric material is an n-type semiconductor.

4. The thermoelectric material according to claim 1, characterized in that A is located at at least one of the interlayer position, void position, and ion position of the Bi-Te compound of the thermoelectric material.

5. Bi, Ch (Ch = Te or Se), and A ２ Q ｘ A step of sealing a reaction mixture containing (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6), heating it to melt and react it; The steps of cooling the result of the reaction to form an ingot; and The step includes crushing the ingot into a powder and then sintering it. A method for forming a thermoelectric material, characterized in that the aforementioned thermoelectric material has the following chemical formula 1. [Chemical formula 1] [(Bi 2 ) m (Bi 2 Ch 3 ) n ] (1-y) / l [A 2 Q x ] y (In the above chemical formula 1, Ch = Te or Se, A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6, 0 < y ≤ 0.4, m represents the number of Bi 2 double layers in the crystallographic unit structure of the thermoelectric material, n represents the number of Bi 2 Ch 3 quintuple layers in the crystallographic unit structure of the thermoelectric material, and is a non-zero number, and l represents the greatest common divisor that can express the composition ratio of Bi and Ch, which are constituent elements of the congeneral series compounds, as an integer.)

6. The method for forming a thermoelectric material according to claim 5, characterized in that the thermoelectric material is polycrystalline.

7. The method for forming a thermoelectric material according to claim 5, characterized in that the reactant is heated at a temperature of 600 to 700°C for 22 to 26 hours.

8. The method for forming a thermoelectric material according to claim 5, characterized in that the sintering is carried out using a discharge plasma sintering method.

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