Low-temperature P-type thermoelectric material and preparation method and application thereof

Abstract

The invention relates to the field of thermoelectric semiconductor materials, and provides a low-temperature P-type thermoelectric material and a preparation method and application thereof in order to solve the significant problem of a P-type thermoelectric material in a low-temperature environment, the chemical formula of the P-type thermoelectric material is Bi < x > Sb < 2-x > Te < 3 > M < y >, x is equal to 0.5-0.7, y is equal to 0.001-0.003, M is selected from one or more of Cu, Pb and Mn, and by means of component optimization and doping design, the P-type thermoelectric material can be prepared into the low-temperature P-type thermoelectric material. According to the P-type thermoelectric material, the thermoelectric performance of the material in the low-temperature region is improved by 18%, and the thermoelectric performance of the material in the low-temperature region is improved to 0.95 at-225 K from 0.75 of general market purchase, and the P-type thermoelectric material can be applied to the field of deep refrigeration.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric semiconductor materials, and in particular to a P-type thermoelectric material for deep cooling and its preparation method. Background Technology

[0002] Thermoelectric cooling technology is based on the Seebeck effect and Peltier effect to achieve the conversion of electricity and heat. It is widely used in fields such as electronic cooling, medical equipment and aerospace. Detection chips often need to operate in low-temperature environments. (Bi,Sb)₂Te₃-based materials are currently common P-type thermoelectric materials used in commercial applications. They exhibit excellent thermoelectric performance near room temperature, and their preparation process is relatively mature and efficient, providing strong support for their widespread application in cryogenic refrigeration. However, to date, research on (Bi,Sb)₂Te₃-based thermoelectric materials has mainly focused on optimizing thermoelectric performance at and above room temperature. These thermoelectric materials with excellent performance at room temperature are insufficient to meet the needs of multi-stage thermoelectric devices below room temperature, and there is an urgent need to improve their thermoelectric performance at low temperatures. Improving the thermoelectric performance of materials at low temperatures requires smaller band gaps and lower carrier concentrations, shifting the peak temperature corresponding to thermoelectric performance to lower temperatures. However, existing P-type bismuth telluride-based thermoelectric materials have significant problems in low-temperature environments (such as 200K-250K): low thermoelectric figure of merit (ZT value), insufficient cooling temperature difference in multilayer thermoelectric refrigeration devices prepared with them, and limited cooling capacity, resulting in poor performance in the field of deep refrigeration and restricting the development of deep refrigeration.

[0003] This is mainly because the (Bi,Sb)₂Te₃ material has a large band gap, resulting in low carrier excitation efficiency and decreased thermoelectric properties at low temperatures. Furthermore, unilaterally reducing the band gap will introduce bipolar diffusion, significantly increasing thermal conductivity and further degrading the material's performance.

[0004] Researchers have conducted numerous attempts to develop thermoelectric materials in the low-temperature region. CN102496676B discloses a niobium-doped bismuth-antimony-based low-temperature thermoelectric material and its preparation method, with the composition formula Bi. 85 Sb 15-x Nb xIn the formula, x is any value between 0 and 15. The preparation method involves mixing Bi, Sb, and Nb powders according to a chemical ratio, and then using mechanical alloying and ultra-high pressure processing. This material exhibits excellent thermoelectric properties near 200K, high mechanical strength, good thermoelectric potential and electrical conductivity, and high quality at low temperatures. The material is stable, has a relatively simple manufacturing process, low cost, and is easy to promote and apply. However, as shown in the attached figure, its ZT value is below 0.35, which is still relatively low. Furthermore, in the Bi, Sb binary phase diagram, although Bi and Sb exhibit continuous solid solutions, the large gap between the liquidus and solidus lines, and the low interdiffusion coefficient between Bi and Sb elements, make it difficult to obtain samples with uniform composition.

[0005] Therefore, there is an urgent need to develop a high-performance, low-temperature p-type bismuth telluride-based thermoelectric material. Summary of the Invention

[0006] To address the significant problems of P-type thermoelectric materials in low-temperature environments, this invention provides a low-temperature P-type thermoelectric material, its preparation method, and its application. By optimizing the composition and doping design, as well as optimizing the preparation process, the thermoelectric performance of the material in the low-temperature region is improved.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: the chemical formula of the low-temperature P-type thermoelectric material is Bi. x Sb 2-x Te3M y Where x = 0.5-0.7, y = 0.001-0.003, and M is selected from one or more of Cu, Pb, and Mn.

[0008] Improving the thermoelectric properties of materials at low temperatures requires smaller band gaps and lower carrier concentrations, while also reducing the influence of bipolar diffusion to shift the peak temperature corresponding to thermoelectric performance to lower temperatures. Bi is selected as the appropriate material. x Sb 2-x Te3M y The addition of M material to the matrix serves two purposes: first, it occupies Te sites, introducing holes and thus increasing the carrier concentration; second, it increases the non-degenerate mobility and effective mass of the valence band density of states. Both of these effectively suppress bipolar diffusion, keeping the thermal conductivity within a reasonable range.

[0009] The preparation method of the above-mentioned P-type thermoelectric material includes the following steps: (1) According to the stoichiometric ratio of Bi, Sb, Te, and M, Bi x Sb 2-x Te3M y Weigh the raw materials, put them into a quartz tube, and vacuum seal the tube. After sealing, place the tube into a swaying furnace for smelting. Finally, take out the quartz tube and cool it in the air. Preferably, Bi, Sb, Te, and M are placed into the quartz tube in order of increasing melting or boiling point. The purity of Bi, Sb, Te, and M is ≥99.99%.

[0010] Preferably, after sealing the tube, the pressure inside the tube should be less than 2 Pa, and the tube should be placed in a swaying furnace for smelting for 1-2 hours at a temperature of 800-1000℃.

[0011] (2) The ingot obtained in step (1) is loaded into the extrusion die and extruded under high temperature and high pressure along the die outlet direction to obtain P-type extruded material; The ingot is directly extruded through a mold, eliminating the need to wait for the mold to cool down slowly and removing the mold. This process is simple, efficient, and cost-effective. Furthermore, due to directional deformation, the grains develop a preferred orientation in that direction, significantly improving carrier mobility. Moreover, the bismuth telluride material deforms under constraint, further increasing the Seebeck coefficient and electrical conductivity while reducing thermal conductivity. This simultaneously and significantly enhances the thermoelectric performance of p-type bismuth telluride-based thermoelectric materials.

[0012] Preferably, the extrusion temperature is 300-500℃ and the pressure is 100-300MPa.

[0013] Preferably, the extrusion ratio of the die is 9-27:1, and the extrusion speed is 1-12 mm / min. When M is selected from Pb or Mn, the extrusion speed is preferably 1-6 mm / min.

[0014] (3) Anneal the P-type extruded material obtained in step (2) under vacuum heating to obtain a low-temperature P-type thermoelectric material; Preferably, the vacuum condition is a pressure below 10. -1 Pa, the annealing temperature is 300-400℃, and the time is 5-15 h.

[0015] By optimizing the composition and doping design to reduce the bandgap while maintaining a suitable carrier concentration, and by optimizing the fabrication process to reduce the lattice thermal conductivity, the thermoelectric performance of the low-temperature material is improved by approximately 18%, from a commercially available 0.75 to a maximum of 0.95@225K. Therefore, the aforementioned low-temperature P-type thermoelectric material can be applied in the field of deep refrigeration.

[0016] Compared with the prior art, the beneficial effects of the present invention are: by optimizing the composition and doping design, bipolar diffusion is suppressed and the carrier concentration is adjusted; by optimizing the preparation process, the thermoelectric performance of the material in the low temperature region is improved, thus solving the bottleneck problem of low cooling performance of multilayer products. Detailed Implementation

[0017] The technical solution of the present invention will be further described below through specific embodiments.

[0018] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available or commonly used in the art. The methods described in the examples, unless otherwise specified, are conventional methods in the art. Unless otherwise indicated, all parts are by weight, temperatures are expressed in °C or at ambient temperature, and pressures are at or near atmospheric pressure. Various variations and combinations of reaction conditions (e.g., component concentrations, required solvents, solvent mixtures, temperature, pressure, and other reaction ranges) and conditions that can be used to optimize the purity and yield of the product obtained by the method exist, requiring only reasonable routine experiments to optimize such method conditions.

[0019] Example 1 (1) Material synthesis High-purity Bi, Sb, Te, and Cu with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Cu 0.002 Weigh out 200g of the elemental substances. Place Bi, Te, Sb, and Cu into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0020] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0021] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360℃ for 10 hours to obtain low-temperature P-type thermoelectric material 1.

[0022] Example 2 (1) Material synthesis High-purity Bi, Sb, Te, and Mn with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi... 0.6 Sb 1.4 Te3Mn 0.002 Weigh out 200g of the elements. In order of increasing melting or boiling point, put Bi, Te, Sb and Mn into a quartz tube. After sealing the tube, make the pressure inside the tube less than 2 Pa. Place the tube in a rocking furnace at 900℃ and rock for 2 hours. Then take out the quartz tube and cool it in the air.

[0023] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0024] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360℃ for 10 hours to obtain low-temperature P-type thermoelectric material 2.

[0025] Example 3 (1) Material synthesis High-purity Bi, Sb, Te, and Cu with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Cu 0.001 Weigh out 200g of the elemental substances. Place Bi, Te, Sb, and Cu into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0026] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0027] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360℃ for 10 hours to obtain low-temperature P-type thermoelectric material 3.

[0028] Example 4 (1) Material synthesis High-purity Bi, Sb, Te, and Cu with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Cu 0.003 Weigh out 200g of the elemental substances. Place Bi, Te, Sb, and Cu into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0029] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0030] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360℃ for 10 hours to obtain low-temperature P-type thermoelectric material 4.

[0031] Example 5: (1) Material synthesis High-purity Bi, Sb, Te, and Cu with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Cu 0.002 Weigh out 200g of the elemental substances. Place Bi, Te, Sb, and Cu into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0032] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 12mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0033] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360℃ for 10 hours to obtain low-temperature P-type thermoelectric material 5.

[0034] Example 6 (1) Material synthesis High-purity Bi, Sb, Te, and Mn with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi... 0.6 Sb 1.4 Te3Mn 0.003 Weigh out 200g of the elements. In order of increasing melting or boiling point, put Bi, Te, Sb and Mn into a quartz tube. After sealing the tube, make the pressure inside the tube less than 2 Pa. Place the tube in a rocking furnace at 900℃ and rock for 2 hours. Then take out the quartz tube and cool it in the air.

[0035] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0036] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360°C for 10 hours to obtain low-temperature P-type thermoelectric material 6.

[0037] Example 7 (1) Material synthesis High-purity Bi, Sb, Te, and Pb with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Pb 0.002 Weigh out 200g of the elemental substances. Place Bi, Pb, Te, and Sb into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0038] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0039] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360℃ for 10 hours to obtain low-temperature P-type thermoelectric material 7.

[0040] Example 8 (1) Material synthesis High-purity Bi, Sb, Te, and Pb with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Pb 0.001 Weigh out 200g of the elemental substances. Place Bi, Pb, Te, and Sb into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0041] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0042] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360°C for 10 hours to obtain low-temperature P-type thermoelectric material 8.

[0043] Example 9 (1) Material synthesis High-purity Bi, Sb, Te, and Pb with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Pb 0.003 Weigh out 200g of the elemental substances. Place Bi, Pb, Te, and Sb into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0044] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0045] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360℃ for 10 hours to obtain low-temperature P-type thermoelectric material 9.

[0046] Example 10 (1) Material synthesis High-purity Bi, Sb, Te, and Pb with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Pb 0.002 Weigh out 200g of the elemental substances. Place Bi, Pb, Te, and Sb into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a swivel furnace at 900℃ and swivel to melt for 2 hours. Then remove the quartz tube and cool it in air.

[0047] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0048] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 360°C for 10 hours to obtain low-temperature P-type thermoelectric material 10.

[0049] Example 11 (1) Material synthesis High-purity Bi, Sb, Te, and Mn with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi... 0.6 Sb 1.4 Te3Mn 0.002 Weigh out 200g of the elements. In order of increasing melting or boiling point, put Bi, Te, Sb and Mn into a quartz tube. After sealing the tube, make the pressure inside the tube less than 2 Pa. Place the tube in a rocking furnace at 1000℃ and rock for 2 hours. Then take out the quartz tube and cool it in the air.

[0050] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 300℃, a certain pressure of 300MPa is applied to the material to keep it at a constant extrusion speed of 5mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 20:1 to obtain P-type extruded material.

[0051] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 400℃ for 7 hours to obtain low-temperature P-type thermoelectric material 11.

[0052] Example 12 (1) Material synthesis High-purity Bi, Sb, Te, and Pb with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Pb 0.002 Weigh out 200g of the elemental substances. Place Bi, Pb, Te, and Sb into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a 1000℃ oscillating furnace and smelt for 2 hours. Then remove the quartz tube and cool it in air.

[0053] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 500°C, a certain pressure of 100MPa is applied to the material to keep it at a constant extrusion speed of 5mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 20:1 to obtain P-type extruded material.

[0054] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 400℃ for 7 hours to obtain low-temperature P-type thermoelectric material 12.

[0055] Example 13 (1) Material synthesis High-purity Bi, Sb, Te, and Cu with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Cu 0.002 Weigh out 200g of the elements. In order of increasing melting or boiling point, place Bi, Te, Sb, and Cu into a quartz tube. After sealing the tube, ensure the pressure inside is less than 2 Pa. Place the tube in a 1000℃ oscillating furnace and smelt for 2 hours. Then, remove the quartz tube and cool it in air.

[0056] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 500°C, a certain pressure of 100MPa is applied to the material to keep it at a constant extrusion speed of 5mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 20:1 to obtain P-type extruded material.

[0057] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 400℃ for 7 hours to obtain low-temperature P-type thermoelectric material 13.

[0058] Example 14 (1) Material synthesis High-purity Bi, Sb, Te, and Cu with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Cu 0.002 Weigh out 200g of the elemental substances. In order of increasing melting or boiling point, place Bi, Te, Sb, and Cu into a quartz tube. After sealing the tube, ensure the pressure inside is less than 2 Pa. Place the tube in a rocking furnace at 800℃ and rock for 2 hours to melt. Then, remove the quartz tube and cool it in air.

[0059] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 300℃, a certain pressure of 300MPa is applied to the material to keep it at a constant extrusion speed of 10mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 25:1 to obtain P-type extruded material.

[0060] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 300℃ for 15 hours to obtain low-temperature P-type thermoelectric material 14.

[0061] Example 15 (1) Material synthesis High-purity Bi, Sb, Te, and Mn with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi... 0.6 Sb 1.4 Te3Mn 0.002 Weigh out 200g of the elements. In order of increasing melting or boiling point, put Bi, Te, Sb and Mn into a quartz tube. After sealing the tube, make the pressure inside the tube less than 2 Pa. Place it in a rocking furnace at 800℃ and rock for 2 hours. Then take out the quartz tube and cool it in the air.

[0062] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 300℃, a certain pressure of 300MPa is applied to the material to keep it at a constant extrusion speed of 6mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 25:1 to obtain P-type extruded material.

[0063] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 300℃ for 15 hours to obtain low-temperature P-type thermoelectric material 15.

[0064] Example 16 (1) Material synthesis High-purity Bi, Sb, Te, and Pb with a purity ≥ 99.99% were selected according to the stoichiometric ratio of Bi. 0.6 Sb 1.4 Te3Pb 0.002 Weigh out 200g of the elemental substances. Place Bi, Pb, Te, and Sb into a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a rocking furnace at 800℃ and rock for 2 hours. Then remove the quartz tube and cool it in air.

[0065] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 300℃, a certain pressure of 300MPa is applied to the material to keep it at a constant extrusion speed of 6mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 25:1 to obtain P-type extruded material.

[0066] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing was carried out at 300℃ for 15 hours to obtain low-temperature P-type thermoelectric material 16.

[0067] Comparative Example 1: No additives added (1) Material synthesis High-purity Bi, Sb, and Te with a purity ≥ 99.99% were combined according to the stoichiometric ratio of Bi... 0.6 Sb 1.4 Weigh 200g of Te3. Place Bi, Te, and Sb in a quartz tube in order of increasing melting or boiling point. Seal the tube to ensure the pressure inside is less than 2 Pa. Place the tube in a 900℃ oscillating furnace and smelt for 1-2 hours. Then remove the quartz tube and cool it in air.

[0068] (2) Ingot extrusion The ingot obtained in step (1) is loaded into the extrusion die. At a high temperature of 400°C, a certain pressure of 200MPa is applied to the material to keep it at a constant extrusion speed of 2mm / min. The material is extruded along the die outlet direction. The extrusion ratio of the die is 15:1 to obtain P-type extruded material.

[0069] (3) Annealing The P-type extruded material obtained in step (2) is subjected to a pressure below 10. -1 Under vacuum conditions of Pa, annealing at 360°C for 10 hours yields a low-temperature P-type thermoelectric material a.

[0070] Comparative Example 2 Commercially available extruded P-type crystal rods (Bi) 0.4 Sb 1.6 Te3). Bi 0.4 Sb 1.6 Te3 is a relatively mature thermoelectric material. Its commercially available p-type thermoelectric material has a zT@225K value of approximately 0.75 at 225K.

[0071] Test case The properties of the P-type extruded materials prepared in Examples 1, 2, 3, 4, and 5, and Comparative Examples 1 and 2 were tested. The thermoelectric figure of merit at 225 K obtained from the tests are shown in Table 1 below. The test conditions and methods are as follows: (1) The total thermal conductivity κ is obtained through κ=DρC p The calculated value is ρ, which is the material density measured by the displacement method, and C. p Specific heat was calculated using the Dulong–Petit law, and D was obtained through testing using a Netzsch LFA 467 device. (2) Conductivity σ and Seebeck coefficient s: obtained using electrical ZEM-3 equipment; (3) Thermoelectric figure of merit zT via zT=s 2 σT / κ is calculated.

[0072] Table 1: Example Components zT@225K Example 1 <![CDATA[Bi 0.6 Sb 1.4 Te3Cu 0.002 ]]> 0.95 Example 2 <![CDATA[Bi 0.6 Sb 1.4 Te3Mn 0.002 ]]> 0.91 Example 3 <![CDATA[Bi 0.6 Sb 1.4 Te3Cu 0.001 ]]> 0.77 Example 4 <![CDATA[Bi 0.5 Sb 1.5 Te3Cu 0.003 ]]> 0.82 Example 5 <![CDATA[Bi 0.6 Sb 1.4 Te3Cu 0.002 ]]> 0.9 Comparative Example 1 <![CDATA[Bi 0.6 Sb 1.4 Te3]]> 0.41 Comparative Example 2 <![CDATA[Commercially available Bi 0.4 Sb 1.6 Te3]]> 0.75 As can be seen from the examples and comparative data in Table 1, adjusting the composition to reduce the bandgap and adjusting the carrier concentration by adding dopants significantly improves the thermoelectric performance. Without adding dopants, the performance is significantly reduced. At the same time, optimizing the preparation process can further improve the material performance in the low-temperature region. The measured zT@225K values ​​are all greater than those of commercially extruded P-type crystal rods.

Claims

1. A low-temperature P-type thermoelectric material, characterized in that, The chemical formula of the low-temperature P-type thermoelectric material is Bi. x Sb 2- x Te3M y Where x = 0.5-0.7, y = 0.001-0.003, and M is selected from one or more of Cu, Pb, and Mn.

2. A method for preparing a low-temperature P-type thermoelectric material as described in claim 1, characterized in that, The preparation method comprises the following steps: (1) According to the stoichiometric ratio of Bi, Sb, Te, and M, Bi x Sb 2-x Te3M y Weigh the raw materials, put them into a quartz tube, and vacuum seal the tube. After sealing, place the tube into a swaying furnace for smelting. Finally, take out the quartz tube and cool it in the air. (2) The ingot obtained in step (1) is loaded into the extrusion die and extruded under high temperature and high pressure along the die outlet direction to obtain P-type extruded material; (3) The P-type extruded material obtained in step (2) is annealed under vacuum heating to obtain a low-temperature P-type thermoelectric material.

3. The method for preparing the low-temperature P-type thermoelectric material according to claim 2, characterized in that, In step (1), Bi, Sb, Te, and M are placed into the quartz tube in order of increasing melting or boiling point.

4. The method for preparing the low-temperature P-type thermoelectric material according to claim 2, characterized in that, Step (1) After sealing the tube, make the pressure inside the tube less than 2 Pa, and put it into the swing furnace for swing melting for 1-2 hours.

5. The method for preparing the low-temperature P-type thermoelectric material according to claim 2 or 4, characterized in that, In step (1), the temperature of the swing furnace is 800-1000℃.

6. The method for preparing the low-temperature P-type thermoelectric material according to claim 2, characterized in that, In step (2), the extrusion temperature is 300-500℃ and the pressure is 100-300MPa.

7. The method for preparing the low-temperature P-type thermoelectric material according to claim 2, characterized in that, Step (2) The extrusion ratio of the mold is 9-27:1, and the extrusion speed is 1-12 mm / min.

8. The method for preparing the low-temperature P-type thermoelectric material according to claim 2 or 7, characterized in that, When M is selected from Pb or Mn, the extrusion speed is preferably 1-6 mm / min.

9. The method for preparing the low-temperature P-type thermoelectric material according to claim 2, characterized in that, The annealing temperature in step (3) is 300-400 ℃ and the time is 5-15 h.

10. An application of the low-temperature P-type thermoelectric material according to claim 1 in deep refrigeration.