Multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material and preparation method thereof

Abstract

The invention relates to the field of thermoelectric materials, and discloses a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material and a preparation method thereof. The chemical formula of the multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material is (Bi0. 5Sb1.5) 1-x / 2PbxTe3-y + zSey, x is larger than or equal to 0.0015 and smaller than or equal to 0.003, y is equal to 0 or 0.15, and z is larger than or equal to 0.1 and smaller than or equal to 0.2. By optimizing the carrier concentration and reducing the lattice thermal conductivity, the performance of the P-type polycrystalline bismuth telluride-based thermoelectric material is remarkably improved, and the room-temperature zT value is improved to 1.1 or above from 0.87 of undoped thermoelectric materials. Compared with an undoped material, the maximum temperature difference of the TEC (the model number is 23020) prepared by adopting the same process can be improved by about 3 DEG C.

Description

Technical Field

[0001] The present invention relates to the field of thermoelectric materials, and in particular to a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material and a preparation method thereof. Background Art

[0002] Bismuth telluride-based materials are currently the only semiconductor thermoelectric materials that have achieved commercial application. Thermoelectric coolers based on bismuth telluride-based materials play an irreplaceable role in medical temperature control, vehicle cooling, civil cooling, optical communication temperature control, and other occasions (for example, CN202510226247.3, CN202411908027.0, etc.). The thermoelectric performance evaluation index of bismuth telluride-based materials is the thermoelectric figure of merit zT, which is calculated by the formula zT = S 2 σ / (κ L +κ e ), where S is the Seebeck coefficient, σ is the conductivity, and κ L is the lattice thermal conductivity, κ e is the electronic thermal conductivity. S, σ and κ e It is closely related to the carrier concentration n of the material. Generally, as n increases, S decreases, and σ and κ e As n decreases, S increases, σ and κ e Decreases. There is an optimal carrier concentration n opt , which can maximize the zT value. In addition, κ L It is a relatively independent parameter that reduces the material's κ L The zT value can also be increased. Therefore, optimizing the carrier concentration and reducing the lattice thermal conductivity are common strategies to improve the performance of bismuth telluride-based materials.

[0003] The mainstream technology for preparing bismuth telluride-based materials is the zone melting technique, which produces highly oriented zone melting materials with high carrier mobility and electrical conductivity. However, zone melting materials also have high lattice thermal conductivity, around 0.95-1.0 W / mK, which suppresses the material's zT value. The room temperature zT value of p-type zone melting materials is around 0.9-1.0, and that of n-type zone melting materials is around 0.9.

[0004] Polycrystalline bismuth telluride-based materials prepared using powder metallurgy can reduce lattice thermal conductivity by introducing abundant grain-boundary enhanced phonon scattering. For example, in a P-type hot-extruded material, the lattice thermal conductivity is reduced to approximately 0.85-0.9 W / mK. However, the theoretical minimum lattice thermal conductivity of bismuth telluride-based materials is 0.31 W / mK, indicating that there is still room for improvement. Summary of the Invention

[0005] To further enhance the performance of P-type polycrystalline bismuth telluride-based materials, this paper proposes a method for improving material performance by doping multiple elements to synergistically optimize carrier concentration and lattice thermal conductivity, based on multi-scale defect design. This simple and easy-to-use method ultimately increases the room temperature zT value of the resulting material from 0.87 to 1.1. Thermoelectric coolers (TECs) fabricated using this P-type polycrystalline bismuth telluride-based thermoelectric material can achieve a maximum temperature difference of approximately 3°C higher than undoped bismuth telluride-based materials prepared using the same process.

[0006] The specific technical solutions of the present invention include: In the first aspect, the present invention provides a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material, the chemical formula of which is (Bi 0.5 Sb 1.5 ) 1-x / 2 Pb x Te 3-y+z Se y , where 0.00150≤x≤0.003, y=0 or 0.15, 0.1≤z≤0.2.

[0007] The P-type polycrystalline bismuth telluride-based thermoelectric material of the present invention is composed of a P-type bismuth telluride matrix and doping elements Pb, Te, and Se, wherein the P-type bismuth telluride matrix adopts traditional components and its chemical formula is Bi 0.5 Sb 1.5 Te3. Due to the narrow band gap of the P-type bismuth telluride matrix (about 0.13eV) and the low carrier concentration, it has an intrinsic excitation phenomenon near room temperature, which reduces the Seebeck coefficient and increases the thermal conductivity, ultimately worsening the zT value of the material. After experiments and analysis, the team of the present invention found that since the number of outermost valence electrons of Pb is smaller than that of Sb and Bi, Pb doping can effectively increase the carrier concentration and suppress intrinsic excitation. However, the doping efficiency of Pb is too high, causing the carrier concentration to exceed the optimal value. Therefore, further doping with Te and Se can reduce the carrier concentration to the optimal value, thereby improving the zT value of the material.

[0008] Furthermore, the doped Te forms a low-melting-point eutectic phase with the p-type bismuth telluride matrix, which melts and extrudes during the high-temperature powder metallurgy process. This enhances the polycrystalline material's preferred grain orientation and improves grain size, thereby improving the material's electrical transport properties. The low-melting-point eutectic phase also forms abundant multi-scale defects during the melt-extrusion process. These, along with the point defects generated by Se doping, reduce the lattice thermal conductivity, further increasing the material's zT value. Ultimately, the room-temperature zT value of the p-type polycrystalline bismuth telluride-based thermoelectric material can be increased from the undoped 0.87 to 1.1, a 26.4% improvement.

[0009] Preferably, in the chemical formula, 0.0015≤x≤0.003, y=0 or 0.15, z=0.2; most preferably, in the chemical formula, x=0.0015, y=0, z=0.2.

[0010] Limiting the values ​​of x, y, and z to the above range can significantly improve the room temperature zT value of P-type polycrystalline bismuth telluride-based thermoelectric materials.

[0011] In a second aspect, the present invention provides a method for preparing a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material, which specifically comprises the following steps: 1) Weigh each element into a container according to the chemical formula, melt it, and cool it to obtain a polycrystalline ingot.

[0012] 2) crushing the polycrystalline ingot, placing it into a mold, hot pressing and sintering it, and cooling it to obtain a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material.

[0013] Preferably, in step 1), the order of adding the elements is Se→Te→Bi→Sb→Pb.

[0014] First of all, considering the problem of element volatilization in the smelting process, the lower the boiling point of the element, the more serious the volatilization. Therefore, the elements with low boiling points are added to the bottom of the container first, and then the elements with higher boiling points are added in sequence to minimize the impact of element volatilization. The boiling points of the elements used in the present invention are ranked from low to high as Se (685°C), Te (988°C), Bi (1564°C), Sb (1587°C), and Pb (1749°C). If the Se and Te elements with low boiling points are added last, the Se and Te element contents in the final material will be low, the carrier concentration will be high, and the zT value will deviate from the optimal value. Secondly, considering that Se and Te may react with Pb during the smelting process to form PbTe and PbSe second phases, affecting the material properties, Se, Te and Pb are separated by Bi and Sb when adding elements, so that the final material phase structure is a pure bismuth telluride phase.

[0015] Preferably, in step 1), the order of adding the elements may also be Pb→40-60% Bi→Te→Se→Sb→the remaining Bi.

[0016] In addition, the present invention further discovered that the melting point and density of elements will also affect the order of addition. Specifically, controlling the elements with low melting point and low density to be added last can ensure that they can wrap other elements with high melting point and high density after melting. The melting points of the elements used in the present invention are arranged from low to high as Se (220.8°C), Bi (271.4°C), Pb (327.5°C), Te (449.5°C), Sb (630.6°C), and the densities are arranged from small to large as Se (4.8g / cm3), Te (6.2g / cm3), Sb (6.7g / cm3), Bi (9.8g / cm3), Pb (11.3g / cm3). It can be found that Bi and Pb are characterized by low melting point but high density. If they are arranged to be added last, they will flow to the lower layer after melting, which may make the melt insufficiently wrapping Te and Sb, and Pb may react to form PbTe and PbSe second phases. Therefore, Pb with the lowest content is added first, and then Bi is added in two times. Te, Se and Sb are added in between the two additions of Bi to allow the melt to react fully and ensure the crystallinity and performance of the material.

[0017] Preferably, in step 2), the temperature of the hot pressing sintering is 450-500°C.

[0018] The present invention discovered that the hot pressing temperature has an important influence on the material properties. The doped Te will form a eutectic phase with the bismuth telluride matrix, and its melting point is approximately around 420°C. Therefore, the hot pressing temperature should be higher than 420°C to ensure the melt extrusion of the eutectic phase. If the temperature is lower than 420°C, the eutectic phase will remain in the material, causing the lattice thermal conductivity to increase and the performance to decrease. The melting point of bismuth telluride-based materials is around 580°C. If the hot pressing temperature is too close to the melting point, part of the powder will melt during the hot pressing process, which will affect the material composition on the one hand and cause serious grain growth on the other hand, both of which will deteriorate the performance. Ultimately, the present invention achieves the best results by controlling the hot pressing temperature within 450-500°C.

[0019] Preferably, in step 1), the container is a quartz tube.

[0020] Preferably, in step 1), each element is placed in a container and then vacuum-sealed.

[0021] Preferably, in step 2), the pulverization is carried out under the protection of an inert atmosphere.

[0022] Preferably, in step 2), the inert atmosphere is argon.

[0023] Preferably, in step 2), the crushing time is 0.5-5 min.

[0024] Preferably, in step 2), the hot pressing sintering is performed under vacuum conditions.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention proposes for the first time the use of a multi-element co-doping method to synergistically optimize the carrier concentration and reduce the lattice thermal conductivity of P-type polycrystalline bismuth telluride-based thermoelectric materials, thereby increasing the room temperature zT value from 0.87 before doping to 1.1.

[0026] (2) The thermoelectric cooler TEC prepared using the P-type polycrystalline bismuth telluride-based thermoelectric material of the present invention, taking the TEC model 23020 as an example, can increase the maximum temperature difference by about 3°C ​​compared with the undoped bismuth telluride-based material prepared by the same process.

[0027] (3) The present invention can further reduce the lattice thermal conductivity of the material and improve the room temperature zT value by optimizing the element loading sequence during the preparation process of P-type polycrystalline bismuth telluride-based thermoelectric material. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Thermoelectric properties of materials with different Pb doping amounts.

[0029] Figure 2 The maximum cooling temperature difference of TEC prepared with materials with different Pb doping amounts.

[0030] Figure 3 Pb-doped 0.003 、Se 0.15 , thermoelectric properties of materials with different Te doping amounts.

[0031] Figure 4 Pb-doped 0.003 、Se 0.15 , SEM images of the cross-section of materials with different Te doping amounts.

[0032] Figure 5 Pb-doped 0.003 、Se 0.15 , the maximum cooling temperature difference of TEC prepared by materials with different Te doping amounts.

[0033] Figure 6 Undoped Bi 0.5 Sb 1.5 Thermoelectric properties of Te3 materials.

[0034] Figure 7 Undoped Bi 0.5 Sb 1.5 The maximum cooling temperature difference of TEC made of Te3 material.

[0035] Figure 8 Thermoelectric properties of materials doped only with Pb.

[0036] Figure 9The maximum cooling temperature difference of the TEC prepared by doping only with Pb material.

[0037] Figure 10 Thermoelectric properties of materials doped with Pb and different Se doping amounts.

[0038] Figure 11 Pb-doped 0.003 、Se 0.15 The maximum cooling temperature difference of the TEC made of the material. DETAILED DESCRIPTION

[0039] To facilitate understanding of the present invention, the present invention is further illustrated below with reference to the following examples, but the present invention is not limited to the following examples.

[0040] Overall embodiment In the first aspect, a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material, the chemical formula of which is (Bi 0.5 Sb 1.5 ) 1-x / 2 Pb x Te 3-y+z Se y , where 0.0015≤x≤0.003, y=0 or 0.15, 0.1≤z≤0.2.

[0041] In some preferred embodiments, in the chemical formula, 0.0015≤x≤0.003, y=0 or 0.15, z=0.2. Most preferably, in the chemical formula, x=0.0015, y=0, z=0.2.

[0042] In a second aspect, a method for preparing a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material comprises the following specific steps: 1) Weigh each element into a container according to the chemical formula, melt it, and cool it to obtain a polycrystalline ingot.

[0043] In some preferred implementation cases, in step 1), the order of adding the elements is Se→Te→Bi→Sb→Pb.

[0044] In some more preferred implementation cases, in step 1), the order of adding the elements may also be Pb→40-60% Bi→Te→Se→Sb→the remaining Bi.

[0045] In some preferred implementation cases, in step 1), the container is a quartz tube.

[0046] In some preferred implementation cases, in step 1), each element is placed into a container and then vacuum-sealed.

[0047] 2) crushing the polycrystalline ingot, placing it into a mold, hot pressing and sintering it, and cooling it to obtain a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material.

[0048] In some preferred implementation cases, in step 2), the temperature of the vacuum hot pressing sintering is 450-500°C.

[0049] In some preferred implementation cases, in step 2), the pulverization is performed under the protection of an inert atmosphere.

[0050] In some preferred implementation cases, in step 2), the inert atmosphere is argon.

[0051] In some preferred implementation cases, in step 2), the crushing time is 0.5-5 min.

[0052] In some preferred implementation cases, in step 2), the hot pressing sintering is performed under vacuum conditions.

[0053] Specific Examples and Comparative Examples Example 1 (I) Effects of Different Pb, Te, and Se Element Combinations and Contents on the Performance of P-Type Polycrystalline Bismuth Telluride-Based Thermoelectric Materials Examples 1-4: Pb and Te co-doped P-type polycrystalline bismuth telluride-based thermoelectric material (undoped with Se), the chemical formula is (Bi 0.5 Sb 1.5 ) 1-x / 2Pb x Te 3+0.2 , x=0.0015 (Example 1), x=0.002 (Example 2), x=0.0025 (Example 3), 0.003 (Example 4).

[0054] The preparation method comprises the following steps: (1) According to the chemical formula (Bi 0.5 Sb 1.5 ) 1-x / 2 Pb x Te 3+0.2 (x=0.0015, 0.002, 0.0025, 0.003) Sequentially weigh the raw materials Te, Bi, Sb, and Pb, and seal them into a clean quartz tube. Evacuate the quartz tube to 10 -3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold was transferred to a hot pressing furnace, evacuated to ≤2 Pa, and hot pressed at 450°C and 50 MPa for 30 min. After cooling, P-type polycrystalline bismuth telluride-based thermoelectric materials with different Pb doping amounts were obtained.

[0055] The P-type polycrystalline bismuth telluride-based thermoelectric material prepared in the above examples 1-4 was cut into 10*10*2mm square pieces along the vertical pressure direction. 3 and 15*3*3mm 3 The test pieces are used to test thermal conductivity, Seebeck coefficient and electrical conductivity respectively. The test errors of thermal conductivity, Seebeck coefficient and electrical conductivity are 4%, 5% and 3% respectively. The thermoelectric properties of different materials are shown in Figure 1 Then cut 1.0mm slices along the vertical pressure direction, and prepare TEC model 23020 according to the same process. The maximum cooling temperature difference tested at 50℃ on the hot end is as follows: Figure 2 shown.

[0056] from Figure 1 and 2 As can be seen from the figure, the zT values ​​of P-type polycrystalline bismuth telluride-based thermoelectric materials at room temperature are around 1.1 for materials with varying Pb doping levels. The maximum cooling temperature difference of the 23020 TEC at a hot end of 50°C is 79.5-80.3°C. Furthermore, as the Pb content decreases, the room-temperature electrical conductivity of the material decreases, leading to a decrease in the total thermal conductivity and an increase in the room-temperature zT value. The sample with a Pb content of 0.0015 exhibits the highest room-temperature zT value and the resulting TEC's cooling temperature difference.

[0057] Example 5-9: P-type polycrystalline bismuth telluride-based thermoelectric materials doped with Pb, Se and different Te doping amounts have the chemical formula (Bi 0.5 Sb 1.5 ) 1-0.0015 Pb 0.003 Te 2.85+z Se 0.15 , z = 0.005 (Example 5), z = 0.01 (Example 6), z = 0.05 (Example 7), z = 0.1 (Example 8), z = 0.2 (Example 9).

[0058] The preparation method comprises the following steps: (1) According to the chemical formula (Bi 0.5 Sb 1.5 ) 1-0.0015 Pb 0.003 Te 2.85+z Se 0.15 (z=0.005, 0.01, 0.05, 0.1, 0.2) Sequentially weigh the raw materials Se, Te, Bi, Sb, and Pb, and seal them into a clean quartz tube. Evacuate the quartz tube to 10- 3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold was transferred to a hot pressing furnace, evacuated to ≤2 Pa, and hot pressed at 450°C and 50 MPa for 30 min. After cooling, P-type polycrystalline bismuth telluride-based thermoelectric materials with different Te doping amounts were obtained.

[0059] Material properties such as Figure 3 As shown in the figure: after doping with Te, the carrier concentration decreases, the Seebeck coefficient increases, and the conductivity decreases; in addition, excess Te forms a low-melting-point eutectic phase in the material, which produces a liquid phase and is squeezed out during the hot pressing process. This process improves the grain orientation and size of the material ( Figure 4 ), keeping the power factor constant; simultaneously, the generation of abundant multi-scale defects enhances phonon scattering and reduces lattice thermal conductivity. Ultimately, the room-temperature zT value of the material gradually increases with increasing Te doping levels. When the Te doping level is 0.2, the maximum zT value reaches 1.07.

[0060] The TEC of 23020 prepared by the same process as Example 1-4 with a Te doping material of 0.2 has a maximum cooling temperature difference of 79.1-80.1℃ at the hot end of 50℃ ( Figure 5 ), the cooling temperature difference of TEC made from the sample with Te doping of 0.2 is the largest.

[0061] Comparative Example 1: Undoped P-type polycrystalline bismuth telluride-based thermoelectric material, chemical formula Bi 0.5 Sb 1.5 Te3.

[0062] The preparation method comprises the following steps: (1) According to the chemical formula Bi 0.5 Sb 1.5 Weigh Te3 raw materials Te, Bi, and Sb in sequence, and seal them into a clean quartz tube. Evacuate the quartz tube to 10 -3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold is transferred to a hot pressing furnace, evacuated to ≤2 Pa, and hot pressed at 450°C and 50 MPa for 30 min. After cooling, an undoped P-type polycrystalline bismuth telluride-based thermoelectric material is obtained.

[0063] Undoped P-type polycrystalline bismuth telluride-based thermoelectric materials have a low power factor due to the unoptimized carrier concentration. At the same time, due to the lack of point defects introduced by doping to scatter phonons, their lattice thermal conductivity is high. Figure 6 As shown, the final room temperature zT value is only 0.87.

[0064] The maximum cooling temperature difference of the 23020 TEC prepared by the same process as in Example 1-4 at the hot end of 50°C is 76.6-77°C ( Figure 7 ).

[0065] Comparative Example 2: P-type polycrystalline bismuth telluride-based thermoelectric material doped only with Pb, the chemical formula is (Bi 0.5 Sb 1.5 ) 1-0.0015 Pb 0.003 Te3.

[0066] The preparation method comprises the following steps: (1) According to the chemical formula (Bi 0.5 Sb 1.5 ) 1-0.0015 Pb 0.003 Weigh Te3 raw materials Te, Bi, Sb, and Pb in sequence, and seal them into a clean quartz tube. Evacuate the quartz tube to 10 -3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold is transferred to a hot pressing furnace, evacuated to ≤2 Pa, and hot pressed at 450°C and 50 MPa for 30 min. After cooling, a P-type polycrystalline bismuth telluride-based thermoelectric material doped with Pb is obtained.

[0067] Material properties such as Figure 8 As shown in the figure: Due to the high doping efficiency of Pb, after doping with only 0.003 atomic ratio of Pb, the carrier concentration of the material is improved, and the room temperature Seebeck coefficient is reduced from 211.8μ V / K of undoped material to 176.3μ V / K. At the same time, the conductivity is increased from 764S / cm of undoped material to 1363S / cm. The final power factor is increased from 3.4×10 -3 W / mK2 Increased to 4.2×10 -3 W / mK 2 ; The point defects introduced by Pb doping scatter phonons, and the lattice thermal conductivity decreases from 0.8W / mK in the undoped state to 0.7W / mK; but because the carrier concentration exceeds the optimal value, the higher conductivity causes the total thermal conductivity of the material to increase significantly, and the final room temperature zT value only increases from 0.87 before doping to 0.92, which is a small increase.

[0068] The maximum cooling temperature difference of the 23020 TEC prepared by the same process as in Example 1-4 at the hot end of 50°C is 76.3-76.5°C ( Figure 9 ).

[0069] Comparative Examples 3-6: P-type polycrystalline bismuth telluride-based thermoelectric material doped with Pb and different Se doping amounts, the chemical formula is (Bi 0.5 Sb 1.5 ) 1- 0.0015 Pb 0.003 Te 3-y Se y , y=0.05 (Comparative Example 3), y=0.1 (Comparative Example 4), y=0.15 (Comparative Example 5), y=0.2 (Comparative Example 6).

[0070] The preparation method comprises the following steps: (1) According to the chemical formula (Bi 0.5 Sb 1.5 ) 1-0.0015 Pb 0.003 Te 3-y Se y (y=0.05, 0.1, 0.15, 0.2) Sequentially weigh the raw materials Se, Te, Bi, Sb, and Pb, and seal them into a clean quartz tube. Evacuate the quartz tube to 10 -3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold was transferred to a hot pressing furnace, evacuated to ≤2 Pa, and hot pressed at 450°C and 50 MPa for 30 min. After cooling, P-type polycrystalline bismuth telluride-based thermoelectric materials with different Se doping amounts were obtained.

[0071] Material properties such as Figure 10As shown: after Se doping, the carrier concentration gradually decreases, the Seebeck coefficient increases, and the conductivity decreases; in addition, the introduction of additional point defect scattering reduces the power factor and lattice thermal conductivity; the room temperature zT value of the final material is slightly reduced. When Se doping is 0.15, the zT value is 0.88.

[0072] The material doped with 0.15 Se was prepared according to the same process as in Example 1-4. The maximum cooling temperature difference of the 23020 TEC at the hot end of 50°C was between 76.3-77.3°C ( Figure 11 ).

[0073] (II) Effects of the order of adding materials and hot pressing temperature during melting on the properties of P-type polycrystalline bismuth telluride-based thermoelectric materials Comparative Example 7: The preparation method comprises the following steps: (1) According to the chemical formula (Bi 0.5 Sb 1.5 ) 1-0.0015 / 2 Pb 0.0015 Te 3+0.2 Weigh the raw materials Bi, Sb, Pb, and Te in sequence, and seal them into a clean quartz tube. Evacuate the quartz tube to 10 -3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold is transferred to a hot pressing furnace, evacuated to ≤2 Pa, and hot pressed at 450°C and 50 MPa for 30 min. After cooling, a P-type polycrystalline bismuth telluride-based thermoelectric material is obtained.

[0074] Comparative Examples 8-9: (1) According to the chemical formula (Bi 0.5 Sb 1.5 ) 1-0.0015 / 2 Pb 0.0015 Te 3+0.2 Sequentially weigh the raw materials Te, Bi, Sb, and Pb, and seal them into a clean quartz tube. Evacuate the quartz tube to 10 -3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold was transferred to a hot pressing furnace, evacuated to ≤2 Pa, and then hot pressed at 400°C (Comparative Example 8) and 570°C (Comparative Example 9) under 50 MPa conditions for 30 min, and cooled to obtain a P-type polycrystalline bismuth telluride-based thermoelectric material.

[0075] Example 10: The difference from Example 1 is that the order of adding elements is different. The preparation method includes the following steps: (1) According to the chemical formula (Bi 0.5 Sb 1.5 ) 1-0.0015 / 2 Pb 0.0015 Te 3+0.2 Weigh the raw materials Pb, Bi(1 / 2), Te, Sb, and Bi(1 / 2) in sequence, and seal them into a clean quartz tube. Evacuate the quartz tube to 10 -3 Pa, sealing the tube with oxyhydrogen flame; (2) The quartz tube containing the raw materials is placed in a rocking furnace at 800°C and smelted for 4 hours. During the smelting process, the tube is rocked to ensure uniformity of the melt and sufficient reaction. After cooling, a polycrystalline ingot is obtained. (3) The polycrystalline ingot was crushed for 1 min in an argon-protected glove box, and the powder was loaded into a metal mold; (4) The mold is transferred to a hot pressing furnace, evacuated to ≤2 Pa, and hot pressed at 450°C and 50 MPa for 30 min. After cooling, a P-type polycrystalline bismuth telluride-based thermoelectric material is obtained.

[0076] The room temperature properties of the materials obtained in Comparative Examples 7-9 and Examples 1 and 10 are shown in Table 1. As can be seen from Table 1, the order of element addition and the hot pressing temperature will affect the material carrier concentration, lattice thermal conductivity and zT value. When the order of element addition is not in accordance with the relationship between boiling point, melting point and density, and when Pb and Te are not separated (Comparative Example 7), the volatilization of the Te element is aggravated, and Pb may react with Te to form a trace amount of PbTe second phase. At the same time, the melt reaction is insufficient, which increases the material carrier concentration and reduces the zT value. After adopting the preferred order of element addition, when the hot pressing temperature is low (Comparative Example 7), the eutectic second phase formed by doping Te and the bismuth telluride matrix is ​​not melted and extruded, resulting in a low carrier concentration, an increase in lattice thermal conductivity, and a decrease in zT value. When the hot pressing temperature is high (Comparative Example 8), there is a partial powder melting phenomenon, which aggravates the grain growth, and Te volatilization is more significant, which increases the material carrier concentration, significantly increases the lattice thermal conductivity, and reduces the zT value. In Examples 1 and 10, the preferred order of element addition and the appropriate hot pressing temperature were used, and the materials obtained an optimized carrier concentration and reduced lattice thermal conductivity, ultimately achieving a high zT value of 1.14. The performance of the material prepared according to the addition order of Example 10 was better than that of Example 1.

[0077] Table 1: Room temperature properties of the materials obtained in Comparative Examples 7-9 and Examples 1 and 10 Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0078] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material, characterized by: The chemical formula is (Bi 0.5 Sb 1.5 ) 1-x / 2Pb x Te 3-y+z Se y , where 0.0015≤x≤0.003, y=0 or 0.15, 0.1≤z≤0.

2.

2. The multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material according to claim 1, characterized in that: The chemical formula is (Bi 0.5 Sb 1.5 ) 1-x / 2 Pb x Te 3-y+z Se y , where 0.0015≤x≤0.003, y=0 or 0.15, z=0.

2.

3. A method for preparing the multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material according to claim 1 or 2, characterized in that include: 1) Weigh each element into a container according to the chemical formula, melt it, and cool it to obtain a polycrystalline ingot; 2) The polycrystalline ingot is crushed, placed in a mold, hot-pressed and sintered, and cooled to obtain a multi-element co-doped P-type polycrystalline bismuth telluride-based thermoelectric material.

4. The preparation method according to claim 3, wherein: In step 1), the order of adding the elements is Se→Te→Bi→Sb→Pb.

5. The preparation method according to claim 3, wherein: In step 1), the order of addition of each element is Pb→40-60%Bi→Te→Se→Sb→the remaining Bi.

6. The preparation method according to claim 3, wherein: In step 2), the hot pressing sintering temperature is 450-500°C.

7. The preparation method according to claim 3, wherein: In step 1), each element is placed into a container and then vacuum-sealed.

8. The preparation method according to claim 3, wherein: In step 2), the pulverization is carried out under the protection of an inert atmosphere.

9. The preparation method according to claim 2, wherein: In step 2), the crushing time is 0.5-5 minutes.

10. The preparation method according to claim 2, characterized in that: In step 2), the hot pressing sintering is performed under vacuum conditions.

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