Thermoelectric materials and methods 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 a thermoelectric material and a method for forming the same.

Background Art

[0002] The thermoelectric phenomenon includes a phenomenon in which heat is transferred by the flow of electrons and holes in a thermoelectric material, and a phenomenon in which the movement of electrons and holes is induced by the movement of heat. This can be applied to various industrial fields such as the cooling field based on the Peltier effect that generates a temperature difference at both ends by an electric current applied to a material, and the power generation field application that utilizes the Seebeck effect in which an electromotive force is generated inside when there is a temperature gradient in the material.

[0003] The power generation and cooling performance of a thermoelectric material is determined by the thermoelectric conversion efficiency of the p-type and n-type semiconductor materials that make up the element. The thermoelectric conversion efficiency is represented by the dimensionless thermoelectric performance index (ZT = σS 2 T / κ) determined by the relationship between the electrical conductivity (σ), the thermal conductivity (κ), the Seebeck coefficient (S), and the absolute temperature (T). The performance index is limited in improvement due to the strong correlation between the constituent variables.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention provides a thermoelectric material having excellent performance.

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

[0006] Other objects of the present invention will become clear from the following detailed description and the accompanying drawings.

Means for Solving the Problems

[0007] 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)

[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 reaction on the reactants containing them.

[0010] The A is located at least at one of the interlayer positions, interstitial positions, and ionic positions 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 Bi, Te, Se, and A2Q x (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6), sealing the reactants containing them, heating and melting them to react, cooling the resultant of the reaction to form an ingot, and pulverizing the ingot into powder and then sintering it.

[0012] The 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)

[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 the spark plasma sintering method.

Advantages of the Invention

[0015] The thermoelectric material according to the 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

Figure 2

Figure 3

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 so that the disclosed content will be thorough and complete and that the idea of the present invention will be fully conveyed to those of ordinary skill 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 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 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 represents a homologous series of compounds composed of a combination of a bilayer of Bi2 and a quintuple layer of Bi2Ch3. m represents the number of bilayers of Bi2 in the crystallographic unit structure of the thermoelectric material, n represents the number of quintuple layers of Bi2Ch3 in the crystallographic unit structure of the thermoelectric material, and l represents the greatest common divisor that can represent the composition ratio of Bi and Ch (Te, Se), which are the constituent elements of the homologous series compound, as an integer.

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

[0021] The thermoelectric material is formed by performing a solid-phase reaction on reactants containing Bi, Te, Se, and A2Q x (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6).

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

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

[0024] The thermoelectric material has the above Chemical Formula 1.

[0025] The reactant is heated at a temperature of 600 to 700 °C for 22 to 26 hours. The sintering is performed using the spark plasma sintering method.

Example

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

[0027] The 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 ratio of m:n:l of Chemical Formula 1 according to the example of the present invention is as follows. This ratio is calculated based on the unit cell structure of each solid compound. ​​(1) m:n:l = 0:3:3, (2) m:n:l = 1:5:4, (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 = 3:0:3

[0028] The thermoelectric material has a composition in which an excess of alkali metal and chalcogen element are present. As a result, the alkali metal atoms are arranged at least at one of the interlayer positions, interstitial positions, or ionic positions of the Bi-Te based compound. Also, based on these defects, the expression of a microstructure of a Bi-Te based homologous compound different from the parent compound is locally induced within the thermoelectric material. For example, BiTe defects or the like can be locally formed within the Bi2Te3 lattice.

[0029] The thermoelectric properties of the thermoelectric material obtained in the above examples were measured. First, for the measurement of electrical transport properties, the pellet sample fabricated by the SPS process was cut and polished to produce a rectangular parallelepiped-shaped specimen of 2.5 mm × 2.5 mm × 10 mm, and the electrical conductivity and Seebeck coefficient were measured. Also, for the measurement of thermal transport properties, the remaining portion of the same pellet sample was cut and polished to produce a disk-shaped specimen with a thickness of 8 mm and a height of 1.5 mm, which was then coated with graphite, and the thermal conductivity was measured.

[0030] As a result of analyzing the thermoelectric material obtained in the examples of the present invention using inductively coupled plasma atomic emission spectrometry, it was shown to have a non-stoichiometric composition as shown in Table 1 below.

[0031]

Table 1

[0032] The thermoelectric material according to an embodiment of the present invention has various point defects and heterogeneous structures introduced while maintaining an overall layered structure. In particular, the alkali metal is arranged at the interlayer position or the interstitial position while maintaining the layered structure peculiar to the Bi-Te-based material, supplies electrons which are additional charge carriers, and induces modulation of the electronic band structure. Thereby, a decrease in electrical conductivity due to alloying is minimized, the Seebeck coefficient is improved, and the overall electrical transport characteristics are maintained. Various forms of point defects such as interlayer positions, interstitial positions, and ionic positions are induced, thereby maximizing phonon scattering through the local expression of heterogeneous Bi-Te-based compounds which are homologous compounds.

[0033] Figure 1 shows a comparison of the PF (power factor) and thermal conductivity of Bi2Te3-9%K2Se6, which is a thermoelectric material according to an embodiment of the present invention, with Bi2Te3, and Figure 2 shows the PF (power factor) and thermoelectric performance index (ZT) thermal conductivity of Bi2Te 3- 9%K2Se6, compared with Bi2Te3.

[0034] Referring to Figures 1 and 2, Bi2Te3-9% K2Se6 maintains excellent electrical transport characteristics reaching about 40 μWcm -1 K -2 at room temperature, while the thermal conductivity decreases to about 0.88 Wm -1 K -1 at 100 °C. Also, Bi2Te3-9% K2Se6 showed a high thermoelectric performance index (ZT) of about 1.4 at 100 °C.

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

[0036] Referring to Figure 3, it was shown that the thermoelectric performance index of the thermoelectric material changes according to the content of A2Q x (Li2Se3, Na2Se3, Li2Se6, Na2Se6) contained in the thermoelectric material and the ratio of alkali metal (Li, Na) to Se. Also, the thermoelectric material according to the embodiment of the present invention shows a high thermoelectric performance index.

[0037] The specific embodiments of the present invention have been discussed above. Those with ordinary knowledge in the technical field to which the present invention pertains will be able to understand that the present invention can be embodied in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative rather than a limiting perspective. The scope of the present invention is shown not in the foregoing description but in the claims, and all differences within the equivalent scope thereof should be construed 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 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.

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)

2. The thermoelectric material according to Claim 1, characterized in that the thermoelectric material has polycrystallinity.

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

4. The thermoelectric material is Bi, Te, Se, and A ２ Q ｘ (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6) is formed by performing a solid-phase compatibility reaction on the reactant containing the same, and the thermoelectric material according to claim 1 is characterized in that.

5. The thermoelectric material according to Claim 1, characterized in that A is located at at least one of an interlayer position, an interstitial position, and an ionic position of a Bi-Te-based compound of the thermoelectric material.

6. Bi, Te, Se, and A ２ Q ｘ Sealing a reactant containing (A = Li, Na, K, Rb, or Cs, Q = S, Se, or Te, x = 1 to 6), and then heating and melting the reactant to cause a reaction; A method for forming a thermoelectric material, comprising: cooling a resultant of the reaction to form an ingot; and sintering the ingot after pulverizing it into powder.

7. The method for forming a thermoelectric material according to Claim 6, characterized in that the 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)

8. The method for forming a thermoelectric material according to Claim 6, characterized in that the thermoelectric material has polycrystallinity.

9. The method for forming a thermoelectric material according to Claim 6, characterized in that the reactants are heated at a temperature of 600 to 700 °C for 22 to 26 hours.

10. The method for forming a thermoelectric material according to Claim 6, characterized in that the sintering is performed using a spark plasma sintering method.

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