A method for preparing high-performance bismuth telluride-based thermoelectric material

Abstract

The present invention relates to the field of thermoelectric semiconductor materials. Aiming at the problem of additional pollution caused by the nano-sizing of materials, a method for preparing high-performance bismuth telluride-based thermoelectric materials is provided, comprising the following steps: 1) performing zone melting directional solidification on a bismuth telluride-based alloy ingot to obtain a crystal rod; 2) performing thermal deformation on the crystal rod obtained in step 1) to obtain a bulk material, wherein the deformation amount is greater than 1, and the thermal deformation is performed under uniaxial pressure, and the pressure direction is perpendicular to the texture direction of the zone melting crystal rod. The present invention thermally deforms the zone melting bulk material through a top-down method, thereby avoiding pollution caused by material refinement, directly introducing nano defects into the bulk material, refining the grains, reducing the thermal conductivity of the material, and improving the mechanical properties and thermoelectric properties of the material.

Description

Technical Field

[0001] The invention relates to the field of thermoelectric semiconductor materials, and in particular to a method for preparing a high-performance bismuth telluride-based thermoelectric material. Background Art

[0002] Thermoelectric materials have great potential in thermoelectric energy conversion and solid-state refrigeration, and have attracted extensive research interest in the past few decades. The material performance can be measured by the thermoelectric figure of merit ZT, which is defined as zT = α 2 σT / κ, where α, σ, κ and T are Seebeck coefficient, electrical conductivity, thermal conductivity and temperature (in Kelvin) respectively. The relationship between electrical conductivity, Seebeck coefficient and thermal conductivity makes it difficult to achieve satisfactory improvement in thermoelectric performance.

[0003] Bismuth telluride (Bi2Te3) is the best thermoelectric material at room temperature. It belongs to the rhombohedral crystal system. Common preparation methods include zone melting method (such as patent CN108550689B "Preparation method of N-type bismuth telluride-based thermoelectric material"), Bridgman method (such as Xu Desheng, "Semiconductor Refrigeration and Application Technology", Shanghai Jiaotong University Press) and single crystal pulling method (such as patent CN113699595A "Recycling and reprocessing method of bismuth telluride-based thermoelectric material producing donor-like effect"), etc. However, the weak van der Waals bond between Te-Te layers in its crystal structure makes it exhibit poor mechanical properties and high lattice thermal conductivity. Nano-sizing has been proven to be one of the most effective ways to improve the thermoelectric and mechanical properties of Bi2Te3-based polycrystalline bulk materials. The common nano-sizing method currently is mechanical alloying method, but in the preparation process, it will introduce additional donor-like effect, affecting the change of material carrier concentration, and as the powder is refined, it is easy for the powder to oxidize and absorb moisture, introducing additional pollution. Therefore, an ideal solution is needed. Summary of the invention

[0004] In order to overcome the problem of additional pollution caused by the material nano-sizing process, the present invention provides a method for preparing a high-performance bismuth telluride-based thermoelectric material. The zone melt bulk material is thermally deformed through a top-down method, thereby avoiding the pollution caused by material refinement, directly introducing nano defects into the bulk material, refining the grains, reducing the thermal conductivity of the material, and improving the mechanical properties and thermoelectric properties of the material.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a high-performance bismuth telluride-based thermoelectric material comprises the following steps:

[0007] 1) performing zone melting and directional solidification on a bismuth telluride-based alloy ingot to obtain a crystal rod;

[0008] 2) The crystal rod obtained in step 1) is subjected to thermal deformation to obtain a bulk material, wherein the deformation amount is greater than 1, and the thermal deformation is carried out under uniaxial pressure, and the pressure direction is perpendicular to the texture direction of the zone melting crystal rod.

[0009] Preferably, the bismuth telluride-based alloy ingot in step 1) is obtained by swing smelting metal raw material powder at 600-700° C. Further preferably, the metal raw material powder is a high-purity powder with a purity of ≥99.99%.

[0010] Preferably, in step 1), the bismuth telluride is Bi 0.5 Sb 1.5 P-type bismuth telluride of Te3+x%wt Te, where x ranges from 0 to 5, or Bi2Te 3-y Se y For N-type bismuth telluride, the value of y ranges from 0.1 to 0.4.

[0011] Preferably, the conditions for the zone melting directional solidification in step 1) are: vacuum degree 0-2 Pa, temperature 600-900 °C, and directional solidification at a speed of 8-35 mm / h.

[0012] Preferably, the crystal rod obtained from the P-type bismuth telluride-based alloy ingot has a zone melting directional solidification temperature of 600-800°C; the crystal rod obtained from the N-type bismuth telluride-based alloy ingot has a zone melting directional solidification temperature of 700-900°C.

[0013] Preferably, the zone melting directional solidification in step 1) is carried out in a glass tube with an inner diameter of 20-30 mm.

[0014] Preferably, in step 2), before the crystal rod is thermally deformed, it is first cut into a thermally deformed precursor, and the cutting direction is perpendicular to the growth direction of the zone melting crystal rod and perpendicular to the grain boundary direction of the crystal rod.

[0015] Preferably, the thermally deformed precursor is a cylinder with a diameter of 15-30 mm. The size of the precursor can be designed according to the size of the mold and the amount of deformation, and is not limited to the above shape.

[0016] Preferably, the thermal deformation in step 2) is performed under the following conditions: 450-550°C and 30-100 MPa uniaxial pressure.

[0017] Preferably, the deformation amount in step 2) ranges from 1 to 9.

[0018] Preferably, in step 2), the thermal deformation is performed in a mold, and the mold is made of graphite, 45 steel or DZ22 alloy.

[0019] Therefore, the beneficial effects of the present invention are as follows: the present invention uses a top-down method to thermally deform the zone melt bulk material, avoiding the pollution caused by material refinement, directly introducing nano defects in the bulk material, refining the grains, reducing the thermal conductivity of the material, improving the mechanical properties and thermoelectric properties of the material, and can improve the thermoelectric properties of the material by more than 20%. Patent CN114031046A uses zone melt samples for extrusion, while this patent is based on single crystal zone melt crystal rods, and then performs thermal deformation in a specific direction instead of hot extrusion, and the deformation direction is inconsistent with the extrusion direction. By introducing nano defects, refining the grains, and reducing thermal conductivity, the thermoelectric and mechanical properties of the material are further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the preparation of the precursor of the present invention;

[0021] Figure 2 It is a comparison chart of the thermoelectric properties of the heat-deformed materials (HD1, HD2) prepared in Example 1 and Example 2 and the zone melting material (ZM) prepared in Comparative Example 1.

[0022] Figure 3 It is a comparison chart of the mechanical properties of the hot deformed materials (HD1, HD2) prepared in Example 1 and Example 2 and the zone melting material (ZM) prepared in Comparative Example 1. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described below through specific embodiments.

[0024] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.

[0025] Overall embodiment

[0026] A method for preparing a high-performance bismuth telluride-based thermoelectric material comprises the following steps:

[0027] 1) Preparation of Bi 0.5 Sb 1.5 P-type bismuth telluride of Te3+x%wt Te, where x ranges from 0 to 5; or B i2 Te 3-y Se y The value of y is in the range of 0.1-0.4. Bi powder, Te powder, Sb powder and Se powder with a purity of ≥99.99% are weighed according to the chemical ratio, and a P-type bismuth telluride-based alloy ingot or an N-type bismuth telluride-based alloy ingot is obtained by swing melting at 600-700 ℃ under vacuum.

[0028] 2) The bismuth telluride-based alloy ingot is placed in a glass tube with an inner diameter of 20-30 mm, and zone melt directional solidification is carried out at a pressure of 0-2 Pa, a temperature of 600-900 ° C (P type at 600-800 ° C, N type at 700-900 ° C) and a speed of 8-35 mm / h to obtain a P-type bismuth telluride-based crystal rod or an N-type bismuth telluride-based crystal rod.

[0029] 3) The crystal rod obtained in step 2) is subjected to thermal deformation in a mold (graphite, 45# steel or DZ22 alloy) to obtain a block material, wherein the deformation amount is greater than 1 (preferably 1-9), the thermal deformation is carried out at 450-550°C and 30-100 MPa uniaxial pressure, and the pressure direction is perpendicular to the texture direction of the zone melting crystal rod;

[0030] Alternatively, the crystal rod obtained in step 2) is first cut into a thermally deformed precursor using a wire cutting machine, with the cutting direction being perpendicular to the growth direction of the zone melting crystal rod and perpendicular to the grain boundary direction of the crystal rod, to obtain a small cylinder with a diameter of 15-30 mm; and then the thermally deformed precursor is subjected to the above-mentioned thermal deformation treatment to obtain a bulk material.

[0031] Example 1

[0032] A method for preparing a high-performance bismuth telluride-based thermoelectric material, comprising the following steps:

[0033] (1) Ingredient smelting / material preparation

[0034] Preparation of Bi 0.5 Sb 1.5 P-type bismuth telluride of Te3+x% wt Te, x is 3, Bi powder, Sb powder and Te powder with purity ≥99.99% are weighed according to the chemical ratio, and high-temperature swing melting at 650℃ under vacuum is obtained to obtain P-type Bi 0.5 Sb 1.5 Te3+3 %wt Te alloy ingot.

[0035] (2) Zone melting

[0036] The alloy ingot obtained in step (1) is placed in a glass tube with an inner diameter of 28 cm, and zone melt directional solidification is carried out at a pressure of 0-2 Pa, 600° C., and a speed of 25 mm / h to obtain a bismuth telluride-based P-type crystal rod.

[0037] (3) Preparation of thermal deformation precursor

[0038] The zone melting crystal rod obtained in step (2) is cut by a wire cutting machine to prepare a hot deformation precursor, such as Figure 1 As shown, the cutting direction is perpendicular to the grain boundary direction of the crystal rod, and a small cylinder (16mm, h28mm) is obtained.

[0039] (4) Thermal deformation preparation

[0040] The thermally deformed precursor obtained in step (3) was placed in a (30 mm) graphite mold, the deformation amount was selected to be 1.5, and then the temperature was raised to 500°C and thermally deformed under a uniaxial pressure of 40 MPa to obtain a (30 mm, h11 mm block material (HD1).

[0041] Example 2

[0042] The difference from Example 1 lies in steps (3) and (4):

[0043] (3) Preparation of thermal deformation precursor

[0044] The zone melting crystal rod obtained in step (2) of Example 1 was cut by a wire saw to prepare a hot deformation precursor, with the cutting direction being perpendicular to the crystal rod grain boundary direction to obtain a small cylinder with a diameter of (16 mm and a height of 18 mm).

[0045] (4) Thermal deformation preparation

[0046] The thermally deformed precursor obtained in step (3) was placed in a (20 mm) graphite mold, the deformation amount was selected to be 1.5, and then the temperature was raised to 500°C and thermally deformed under a uniaxial pressure of 40 MPa to obtain a (20 mm, h8 mm) block material (HD2).

[0047] Comparative Example 1

[0048] The difference from Example 1 is that step (4) is not performed, that is, no thermal deformation treatment is performed, and the obtained product is a zone melt material (ZM).

[0049] Example 3

[0050] A method for preparing a high-performance bismuth telluride-based thermoelectric material, comprising the following steps:

[0051] (1) Ingredient smelting / material preparation

[0052] Preparation of Bi2Te 3-y Se y N-type bismuth telluride, y is 0.3, Bi powder, Se powder and Te powder with purity ≥99.99% are weighed according to the chemical ratio, and N-type Bi is obtained by swing melting at 700 ℃ under vacuum. 0.5 Te 2.7 Se 0.3 Alloy ingots.

[0053] (2) Zone melting

[0054] The alloy ingot obtained in step (1) is placed in a glass tube with an inner diameter of 28 cm, and zone melt directional solidification is carried out at a pressure of 0-2 Pa, 700° C., and a speed of 25 mm / h to obtain a bismuth telluride-based N-type crystal rod.

[0055] (3) Preparation of thermal deformation precursor

[0056] The zone melting crystal rod obtained in step (2) was cut by a wire cutting machine to prepare a hot deformation precursor, with the cutting direction being perpendicular to the crystal rod grain boundary direction to obtain a small cylinder (16 mm, h18 mm).

[0057] (4) Thermal deformation preparation

[0058] The thermally deformed precursor obtained in step (3) was placed in a (20 mm) graphite mold, the deformation amount was selected to be 1.5, and then the temperature was raised to 500°C and thermally deformed under a uniaxial pressure of 40 MPa to obtain a (20 mm, h11 mm block material (HD1).

[0059] Example 4

[0060] (1) Ingredient smelting / material preparation

[0061] Preparation of Bi 0.5 Sb 1.5 P-type bismuth telluride of Te3+x% wt Te, where x is 3, is prepared by weighing Bi powder, Sb powder and Te powder with a purity of ≥99.99% according to the chemical ratio, and then smelting them at 650 ℃ under vacuum to obtain P-type Bi 0.5 Sb 1.5 Te3+3 %wt Te alloy ingot.

[0062] (2) Zone melting

[0063] The alloy ingot obtained in step (1) is placed in a glass tube with an inner diameter of 28 cm, and zone melt directional solidification is carried out at a pressure of 0-2 Pa, 600° C., and a speed of 25 mm / h to obtain a bismuth telluride-based P-type crystal rod.

[0064] (3) Thermal deformation preparation

[0065] The crystal rod obtained in step (2) is placed in a square mold with a length, width and height of 40*60*50 mm, with a deformation amount of 2.2, and then the temperature is raised to 500 °C and hot deformed under a uniaxial pressure of 40 MPa to obtain a block material with a length, width and height of 40*60*12 mm.

[0066] Performance Characterization

[0067] like Figure 2 , 3 As shown, the bismuth telluride-based thermoelectric material prepared by the present invention has excellent mechanical properties and thermoelectric properties, and can improve the thermoelectric properties of the material by more than 20%. The hardness test condition is to use a pyramid head with a force of 0.3 kg to make an indentation on the block sample, and the indentation diagonal length is calculated. The larger the value, the higher the hardness.

[0068] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-performance bismuth telluride-based thermoelectric material, characterized in that: Includes steps: 1) The bismuth telluride-based alloy ingot is subjected to zone melting and directional solidification to obtain a crystal rod; 2) Cut the crystal rod into a hot-deformed precursor, with the cutting direction being perpendicular to the growth direction of the zone melt crystal rod and the grain boundary direction of the crystal rod; the precursor is hot-deformed at 450-550 °C and 30-100 MPa uniaxial pressure to obtain a bulk material with a deformation amount of 1-9 and a pressure direction perpendicular to the texture direction of the zone melt crystal rod.

2. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 1, characterized in that: Step 1) The bismuth telluride-based alloy ingot is obtained by swing melting of metal raw material powder at 600-700°C.

3. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 1 or 2, characterized in that: Step 1) The bismuth telluride is Bi 0.5 Sb 1.5 P-type bismuth telluride of Te3+x%wt Te, where x ranges from 0 to 5.

4. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 1 or 2, characterized in that: Step 1) The bismuth telluride is Bi2Te 3-y Se y For N-type bismuth telluride, the value of y ranges from 0.1 to 0.

4.

5. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 1, characterized in that: Step 1) The conditions for the zone melt directional solidification are: vacuum degree 0-2 Pa, temperature 600-900 °C, and directional solidification at a speed of 8-35 mm / h.

6. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 3, characterized in that: The temperature of the zone melting directional solidification of the crystal rod obtained from the P-type bismuth telluride-based alloy ingot is 600-800°C.

7. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 4, characterized in that: The temperature of the zone melting directional solidification of the crystal rod obtained from the N-type bismuth telluride-based alloy ingot is 700-900°C.

8. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 1, characterized in that: Step 1) The zone melting directional solidification is carried out in a glass tube with an inner diameter of 20-30 mm.

9. The method for preparing a high-performance bismuth telluride-based thermoelectric material according to claim 1, characterized in that: The thermal deformation precursor is a cylinder with a diameter of 15-30 mm.

Images