N-type Mg3Bi2-based composite thermoelectric material as well as preparation method and application thereof

Abstract

The invention provides an n-type Mg3Bi2-based composite thermoelectric material as well as a preparation method and application thereof, the chemical composition of the n-type Mg3Bi2-based composite thermoelectric material is Mg 3.2 (Bi 0.7 Sb 0.3) 1.99 Te 0.01-Q2Se x wt%, Q is Cu and / or Ag element, and the sum of x wt% and x wt% is 100%. X is 0.0 lt; and x is less than or equal to 1.5. The invention also discloses a preparation method and application of the n-type Mg3Bi2-based composite thermoelectric material. The Fermi level of the n-type Mg3Bi2-based composite thermoelectric material goes deep into a conduction band, the electrical property is excellent, and the power factor is kept at a high level; the total thermal conductivity is reduced, so that the thermoelectric figure of merit of the n-type Mg3Bi2-based thermoelectric material is remarkably improved, and the n-type Mg3Bi2-based thermoelectric material has a wide application prospect in the field of semiconductor thermoelectric materials.

Description

Technical Field

[0001] The present invention relates to the technology of thermoelectric materials, and particularly to an n-type Mg 3 Bi 2 -based composite thermoelectric material, a preparation method thereof, and uses thereof. Background Art

[0002] Thermoelectric materials are a type of green and environmentally friendly functional materials that can directly convert thermal energy and electrical energy into each other. The energy conversion performance of thermoelectric materials (TE) is determined by the dimensionless figure of merit ZT = S 2 σT / κ tot , where S is the Seebeck coefficient, T is the absolute temperature, σ is the electrical conductivity, and κ tot is the total thermal conductivity, which generally includes the electronic thermal conductivity κ ele and the lattice thermal conductivity κ lat .

[0003] Although traditional Bi 2 Te 3 -based thermoelectric materials have relatively high ZT values, their large-scale applications are limited due to their high costs, the scarcity and toxicity of the Te element. In contrast, Mg 3 Bi 2 -based materials have the advantages of rich raw materials, non-toxicity, and low costs. However, the electrical conductivity of intrinsic Mg 3 Bi 2 is relatively low, and it is prone to thermal decomposition and oxidation at high temperatures, which limits its practical applications.

[0004] Therefore, developing a new type of n-type Mg 3 Bi 2 -based composite thermoelectric material and a preparation method thereof has important scientific significance and application value. By optimizing the material composition and structure design and combining with an efficient preparation process, it is expected to achieve high-performance, low-cost, and environmentally friendly thermoelectric materials, and promote their practical applications in fields such as waste heat recovery and thermoelectric power generation. Summary of the Invention

[0005] The object of the present invention is to propose an n-type Mg 3 Bi 2 -based composite thermoelectric material in view of the problems that the electrical conductivity of traditional Mg 3 Bi 2 -based thermoelectric materials is relatively low, and it is prone to thermal decomposition and oxidation at high temperatures, which limits its practical applications. The Fermi level of this material penetrates deep into the conduction band, and it has excellent electrical properties, and the power factor remains at a relatively high level; the total thermal conductivity is reduced, thereby significantly improving the thermoelectric figure of merit of the n-type Mg 3 Bi 2 -based thermoelectric material, and showing broad application prospects in the field of semiconductor thermoelectric materials.

[0006] It should be noted that in the present invention, unless otherwise specified, the specific meaning of "including" involved in the composition limitation and description includes both the open "including", "containing" and their similar meanings, and also the closed "consisting of", "composed of" and their similar meanings.

[0007] To achieve the above object, the technical solution adopted by the present invention is: an n-type Mg 3 Bi 2 -based composite thermoelectric material, with a chemical composition of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Q 2 Sexwt%, where Q is Cu and / or Ag element; x is 0.0 < x ≤ 1.5; the subscript is the molar ratio, that is, the molar ratio of Mg, Bi, Sb, Te is 3.2:1.393:0.597:0.01. The n-type Mg 3 Bi 2 -based composite thermoelectric material contains wt% of Q 2 Se.

[0008] Furthermore, x is 0.5 ≤ x ≤ 1.5.

[0009] Another object of the present invention also discloses a preparation method of an n-type Mg 3 Bi 2 -based composite thermoelectric material, and this preparation method has the advantages of low cost, simple process, low equipment requirements, etc.

[0010] Specifically, the preparation method of the n-type Mg 3 Bi 2 -based composite thermoelectric material includes the following steps:

[0011] (1) In an inert atmosphere with a water oxygen content lower than 1 ppm, ball-mill Mg particles, Bi powder, Sb particles, Te particles, Cu 2 Se particles and / or Ag 2 Se particles according to the chemical composition to obtain a precursor powder;

[0012] (2) Sinter the precursor powder obtained in step (1) to obtain an n-type Mg 3 Bi 2 -based composite thermoelectric material.

[0013] Furthermore, the inert atmosphere in step (1) is high-purity argon.

[0014] Further, the purity of the Mg particles in step (1) is greater than or equal to 99.995%, the purity of the Bi powder is greater than or equal to 99.999%, the purity of the Sb particles is greater than or equal to 99.999%, the purity of the Te particles is greater than or equal to 99.99%, Cu 2 Se particle purity is greater than or equal to 99.999%, Ag 2 Se particle purity is greater than or equal to 99.999%.

[0015] Further, the ball milling in step (1) is high-energy ball milling, the ball milling speed is 1000 - 1500 rpm / min, and the ball milling time is 10 - 14 h. A SPEX-8000D high-energy ball mill with a rotation speed greater than 500 rpm / min can be selected as the ball mill.

[0016] Further, the sintering in step (2) is high-temperature spark plasma sintering.

[0017] Further, the vacuum degree of the high-temperature spark plasma sintering in step (2) is 0.1 - 10 Pa.

[0018] Further, the sintering temperature in step (2) is 600 - 700 °C, the sintering pressure is 20 - 50 MPa, and the sintering time is 1 - 10 min.

[0019] Further, after the sintering in step (2), it is cooled with the furnace.

[0020] Another object of the present invention also discloses the use of an n-type Mg 3 Bi 2 -based composite thermoelectric material in the field of semiconductor thermoelectric materials.

[0021] The n-type Mg 3 Bi 2 -based composite thermoelectric material, its preparation method and use of the present invention have the following advantages compared with the prior art:

[0022] 1) The n-type Mg 3 Bi 2 -based composite thermoelectric material of the present invention makes the Fermi level penetrate deep into the conduction band by compounding with Cu 2 Se and / or Ag 2 Se, obtaining excellent electrical properties. At the same time, it maintains a high power factor and effectively reduces the total thermal conductivity, thereby significantly improving the thermoelectric figure of merit of the n-type Mg 3 Bi 2 -based thermoelectric material. At 523 K, the thermoelectric figure of merit of the n-type Mg 3 Bi 2 -based thermoelectric material is 0.7 - 1.2. For example, at 523 K, Mg 3.2 (Bi 0.7 Sb0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.0 wt% and Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 The thermoelectric figure of merit of Se 1.0 wt% reaches 1.12 and 1.09 respectively.

[0023] 2) The n-type Mg 3 Bi 2 -based composite thermoelectric material of the present invention can optimize the Seebeck coefficient, reduce the thermal conductivity, and thus improve the thermoelectric performance. For example, at 523 K, Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.0 wt% and Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 The Seebeck coefficients of Se 1.0 wt% are increased to -239.39 WμV K -1 and -225.99 WμV K -1 . Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.0 wt% and Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 The thermal conductivities of Se 1.0 wt% are reduced to 0.90 W m -1 K -1 and 0.93 W m -1 K -1 .

[0024] 3) The preparation method of the n-type Mg 3 Bi 2 -based composite thermoelectric material of the present invention has the advantages of low cost, simple process, and low equipment requirements.

[0025] 4) The n-type Mg 3 Bi 2The base composite thermoelectric material has good application prospects and large-scale popularization potential in the field of semiconductor thermoelectric materials. Description of the Drawings

[0026] Figure 1 XRD patterns of the thermoelectric materials obtained in the comparative example and the examples;

[0027] Figure 2 For the composite Cu 2 Seebeck coefficients of the thermoelectric materials obtained in Examples 1-3 of the composite Cu

[0028] Figure 3 For the composite Ag 2 Seebeck coefficients of the thermoelectric materials obtained in Examples 4-6 of the composite Ag

[0029] Figure 4 For the composite Cu 2 Power factors of the thermoelectric materials obtained in Examples 1-3 of the composite Cu

[0030] Figure 5 For the composite Ag 2 Power factors of the thermoelectric materials obtained in Examples 4-6 of the composite Ag

[0031] Figure 6 For the composite Cu 2 Thermal conductivities of the thermoelectric materials obtained in Examples 1-3 of the composite Cu

[0032] Figure 7 For the composite Ag 2 Thermal conductivities of the thermoelectric materials obtained in Examples 4-6 of the composite Ag

[0033] Figure 8 For the composite Cu 2 Thermoelectric figure of merit of the thermoelectric materials obtained in Examples 1-3 of the composite Cu

[0034] Figure 9 For the composite Ag 2 Thermoelectric figure of merit of the thermoelectric materials obtained in Examples 4-6 of the composite Ag Detailed Embodiments

[0035] Hereinafter, the present invention will be further described with reference to the examples. The description of the technical features recorded below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0036] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the systematic errors that are inevitable in industrial production.

[0037] In this specification, the numerical range expressed as "numerical value A to numerical value B" means a range including the endpoint numerical values A and B.

[0038] In this specification, the numerical range expressed as "above" or "below" means a numerical range including this number.

[0039] In this specification, the meaning expressed by "may" includes the meanings of both performing a certain process and not performing a certain process.

[0040] In this specification, the use of "optional" or "optional" means that certain substances, components, execution steps, applied conditions and other factors are used or not used.

[0041] In this specification, when "normal temperature" or "room temperature" is used, the temperature can be 15 - 25 °C.

[0042] In this specification, for the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0043] The present invention provides an n-type Mg 3 Bi 2 -based composite thermoelectric material, with a chemical composition of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Q 2 Se x wt%; where Q is Cu and / or Ag element; 0.0 < x ≤ 1.5, and x is specifically preferably 0.5, 1.0, 1.5.

[0044] The present invention provides a preparation method for the n-type Mg 3 Bi 2 -based composite thermoelectric material as described in the above technical solution, comprising the following steps:

[0045] In an inert atmosphere with a water and oxygen content below 1 ppm, Mg particles, Bi powder, Sb particles, Te particles, Cu 2 Se particles and / or Ag 2 Se particles are ball-milled according to the chemical element composition to obtain a precursor powder;

[0046] The precursor powder is sintered to obtain an n-type Mg 3 Bi 2 -based composite thermoelectric material;

[0047] Unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0048] In the present invention, the metal Mg is preferably Mg particles with a purity preferably of 99.995%; the metal Bi is preferably Bi powder with a purity preferably of 99.999%; the metal Sb is preferably Sb particles with a purity preferably of 99.999%; the Cu 2 Se has a purity preferably of 99.999%, and the Ag 2 Se has a purity preferably of 99.99%.

[0049] In the present invention, the inert atmosphere is preferably high-purity argon.

[0050] The ball milling in step (1) is high-energy ball milling. The ball mill is a SPEX-8000D ball mill with a rotation speed greater than 500 rpm / min, and the ball milling time is 10 - 14 h.

[0051] The sintering in step (2) is high-temperature spark plasma sintering.

[0052] The sintering conditions in step (2) include: a temperature of 600 - 700 °C, a pressure of 20 - 50 MPa, and a time of 1 - 10 min; then it is cooled with the furnace.

[0053] The vacuum degree of the high-temperature spark plasma sintering in step (2) is 0.1 - 10 Pa.

[0054] During specific implementation, the powder in the spark plasma sintering process is placed in a graphite mold.

[0055] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in combination with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0056] Example 1

[0057] This example discloses an n-type Mg 3 Bi 2 -based composite thermoelectric material, whose chemical composition is Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 0.5 wt%, and a preparation method of the n-type Mg 3 Bi 2 -based composite thermoelectric material, including the following steps:

[0058] According to Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2Weigh 8 g of Mg particles, Bi powder, Sb particles, Te particles and Cu with a stoichiometric ratio of 0.5 wt% Se in an argon atmosphere with water and oxygen content below 1 ppm. 2 Put the Se particles into a ball milling jar, place it on a high-energy ball mill and mix and stir for 12 h at a stirring rate of 1500 r / min.

[0059] Put the uniformly mixed precursor powder into a graphite mold in an inert atmosphere, and quickly transfer it to a spark plasma sintering device. Sinter it at a pressure of 30 MPa and a temperature of 650 °C for 3 min to obtain Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 0.5 wt%.

[0060] Example 2

[0061] This example discloses an n-type Mg 3 Bi 2 -based composite thermoelectric material with a chemical composition of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.0 wt%, and its preparation method is the same as that of Example 1.

[0062] Example 3

[0063] This example discloses an n-type Mg 3 Bi 2 -based composite thermoelectric material with a chemical composition of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.5 wt%, and its preparation method is the same as that of Example 1.

[0064] Example 4

[0065] This example discloses an n-type Mg 3 Bi 2 -based composite thermoelectric material with a chemical composition of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 Se 0.5 wt%, and its preparation method is the same as that of Example 1.

[0066] Example 5

[0067] This example discloses an n-type Mg 3 Bi 2 -based composite thermoelectric material, whose chemical composition is Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 Se 1.0 wt%, and its preparation method is the same as that of Example 1.

[0068] Example 6

[0069] This example discloses an n-type Mg 3 Bi 2 -based composite thermoelectric material, whose chemical composition is Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 Se 1.5 wt%, and its preparation method is the same as that of Example 1.

[0070] Comparative Example 1

[0071] This Comparative Example 1 discloses a composite thermoelectric material, which is different from Example 1 in that it does not incorporate Cu 2 Se particles or Ag 2 Se particles, and its chemical composition is Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 , and its preparation method is the same as that of Example 1.

[0072] The composite thermoelectric materials of Examples 1-6 and Comparative Example 1 were respectively tested, and the test methods and results are as follows:

[0073] Figure 1 XRD patterns of the thermoelectric materials obtained in Examples 1-6 and Comparative Example 1 are shown. It can be seen that the main phases present in the sintered Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Q 2 Se x wt% thermoelectric material samples are the characteristic diffraction peaks of Mg 3 Bi 2 (space group P-3m1).

[0074] The thermoelectric materials obtained in Examples 1-6 and Comparative Example 1 were tested for electrical properties using an LSR-3 electrical property test system. The test curves of the Seebeck coefficient are as shown in Figure 2 and Figure 3 , and the test curves of the power factor are as shown in Figure 4 and Figure 5 . It can be seen from Figures 2 to 5 that compared with the comparative example without composite Cu 2 Se or Ag 2 Se particles, the thermoelectric materials obtained in the present invention have higher Seebeck coefficients and power factors. The Seebeck coefficient is increased from -201.00 μV K -1 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 in the comparative example at 523 K to -239.39 μW V K -1 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.0 wt% in Example 2, and -225.99 μW V K -1 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 Se 1.0 wt% in Example 5. The power factor is increased from 19.80 μW cm -1 K -2 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 in the comparative example at room temperature to 20.33 μW cm -1 K -2 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.0 wt% in Example 2.

[0075] The thermal diffusivity D of the sample was measured using the laser flash method (LFA-457 laser thermal conductivity meter), combined with the density ρ and heat capacity C of the sample measured by the Archimedes drainage method p , and the total thermal conductivity κ was calculated according to the following formula total = D Cp ρ。 Figure 6 and Figure 7 are the thermal conductivity diagrams of the thermoelectric materials obtained in Examples 1-6 and Comparative Example 1. It can be seen from Figure 6 that the thermal conductivity at 523 K decreases from 1.16 W m 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 in the comparative example to 0.90 W m -1 K -1 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2 Se 1.0 wt% in Example 5. It can be seen from -1 K -1 that the thermal conductivity at 523 K decreases from 1.16 W m Figure 7 in the comparative example to 0.93 W m 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 in the comparative example to 0.93 W m -1 K -1 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 Se 1.0 wt% in Example 5. -1 K -1 .

[0076] The thermoelectric figure of merit of the thermoelectric materials obtained in Examples 1-6 and Comparative Example 1 is calculated using the formula ZT = S 2 σT / κ tot . Figure 8 and Figure 9 are the thermoelectric figure of merit diagrams of the thermoelectric materials obtained in Examples 1-6 and Comparative Example 1. It can be seen from Figure 8 that the thermoelectric figure of merit at 523 K increases from 0.98 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 in the comparative example to the value of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Cu 2The 1.12 of 1.0 wt% Se. From Figure 9 As can be seen, the figure of merit of thermoelectricity at 523K is increased from 0.98 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 in the comparative example to 1.09 of Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Ag 2 Se 1.0 wt%.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An n-type Mg3Bi2-based composite thermoelectric material, characterized in that: Chemical composition: Mg 3.2 (Bi 0.7 Sb 0.3 ) 1.99 Te 0.01 -Q2Se x wt%, where Q is Cu and / or Ag element; x is 0.0 <x≤1.5。 2. The n-type Mg3Bi2-based composite thermoelectric material according to claim 1, characterized in that: x is 0.5≤x≤1.

5.

3. A method for preparing the n-type Mg3Bi2-based composite thermoelectric material according to claim 1 or 2, characterized in that: The following steps are involved: (1) In an inert atmosphere with a water and oxygen content of less than 1 ppm, Mg particles, Bi powder, Sb particles, Te particles, Cu2Se particles and / or Ag2Se particles are ball-milled according to the chemical element composition to obtain a precursor powder; (2) Sintering the precursor powder obtained in step (1) to obtain an n-type Mg3Bi2-based composite thermoelectric material.

4. The method for preparing the n-type Mg3Bi2-based composite thermoelectric material according to claim 3, characterized in that: The inert atmosphere in step (1) is high-purity argon.

5. The method for preparing the n-type Mg3Bi2-based composite thermoelectric material according to claim 3, characterized in that: The ball milling in step (1) is high-energy ball milling, the ball milling speed is 1000-1500 rpm / min, and the ball milling time is 10-14 h.

6. The method for preparing the n-type Mg3Bi2-based composite thermoelectric material according to claim 3, characterized in that: The sintering in step (2) is high temperature discharge plasma sintering.

7. The method for preparing the n-type Mg3Bi2-based composite thermoelectric material according to claim 6, characterized in that: The vacuum degree of the high temperature discharge plasma sintering in step (2) is 0.1-10Pa.

8. The method for preparing the n-type Mg3Bi2-based composite thermoelectric material according to claim 3, characterized in that: In step (2), the sintering temperature is 600-700° C., the sintering pressure is 20-50 MPa, and the sintering time is 1-10 min.

9. The method for preparing the n-type Mg3Bi2-based composite thermoelectric material according to claim 3, characterized in that: After the sintering in step (2), the furnace is cooled.

10. Use of the n-type Mg3Bi2-based composite thermoelectric material according to claim 1 or 2 in the field of semiconductor thermoelectric materials.

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