Bismuth telluride-based thermoelectric material and preparation method and application thereof

Abstract

The invention belongs to the technical field of thermoelectric semiconductor materials, and relates to a bismuth telluride-based thermoelectric material and a preparation method and application thereof. Bi < 0.48 > Sb < 1.52 > Te < 3 + > 3 wt% Te + x wt% Cu2Se is prepared through melting swing, zone melting, crushing and pressing, hot extrusion forming and the like, x is greater than or equal to 0 and less than or equal to 0.1, and the room-temperature carrier concentration is (3.1-5.5) * 10 < 19 > cm <-3 >; the conductivity at room temperature is 770 to 1553 S / cm; the thermal conductivity is 0.96-0.97 Wm <-1 > K <-1 >; the mu W / kappa l value is 0.15 m < 3 > KV <-1 > s <-1 > W <-1 >; and the thermoelectric figure of merit zT is not less than 1.0 (300-400 K). Specifically, a hot extrusion method is combined with Cu2Se doping, grain orientation is optimized by using a hot extrusion process, a densified microstructure is formed, grain boundary thermal resistance is reduced, and the Cu2Se-based composite material is suitable for industrial waste heat recovery and miniature refrigeration devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric semiconductor materials, and specifically relates to a bismuth telluride-based thermoelectric material and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Based on the Seebeck effect and the Peltier effect, thermoelectric materials can directly convert heat energy into electrical energy, and have great application prospects in the fields of low-quality waste heat, waste heat recovery, and precise temperature control. zT Measure, its expression is zT = σS 2 T / κ .in, σ, S, T, κ and σS 2 They are electrical conductivity, Seebeck coefficient, absolute temperature, thermal conductivity and power factor ( PF = σS 2 The quality can be measured by the weight average mobility μ W measure). κ The electronic thermal conductivity dominated by the carriers ( κ e ) and the lattice thermal conductivity dominated by lattice vibration ( κ l ).However, σ, S and κ e Because the carrier and electron band structures are coupled together, it is difficult to achieve a synergistic improvement of the three parameters; the difference is that κ l are relatively independent. Therefore, μ W / κ l The ratio can be used to measure the thermoelectric performance.

[0004] Bismuth telluride-based materials with layered structures have excellent thermoelectric properties and have achieved significant applications in near-room temperature power generation and refrigeration. The layered structure also makes the thermoelectric transmission characteristics of bismuth telluride extremely anisotropic. Currently, most commercial bismuth telluride materials are prepared by zone melting methods. The bismuth telluride crystals prepared by this method have extremely high orientation and power factor. However, high crystal structure orientation is accompanied by extremely high thermal conductivity. It can be seen from the thermoelectric figure of merit calculation formula that high thermal conductivity partially offsets the effect of high power factor on the improvement of thermoelectric figure of merit, which also limits the thermoelectric performance of bismuth telluride materials prepared by zone melting. Existing technologies such as vacuum hot pressing, thermal deformation, and hot pressing texturing have effectively reduced the thermal conductivity of the material, but their electrical properties are lower than those of zone melting samples, so their comprehensive thermoelectric performance still needs to be improved.

[0005] Furthermore, existing technologies exist that effectively control the carrier concentration of materials by doping them with compounds. However, due to the coupling between carriers and electronic band structures in parameters related to thermoelectric performance, it is difficult to achieve synergistic improvements in multiple parameters (such as electrical conductivity, thermal conductivity, and Seebeck coefficient), thus preventing significant improvements in thermoelectric performance. Therefore, those skilled in the art urgently need to develop a bismuth telluride thermoelectric material with excellent thermoelectric performance. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention aims to provide a bismuth telluride-based thermoelectric material and its preparation method and application. The bismuth telluride-based thermoelectric material prepared in this application is specifically achieved by optimizing the material composition and process parameters to achieve high electrical performance and low thermal conductivity, that is, high μ W / κ l value, and significantly improved the thermoelectric figure of merit.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions: In a first aspect of the present invention, a bismuth telluride-based thermoelectric material is provided, wherein the chemical composition of the thermoelectric material is: Bi 0.48 Sb 1.52 Te3+3 wt%Te+ x wt% Cu2Se, wherein 0≤x≤0.1, and the material has at least one of the following properties: The carrier concentration at room temperature is 3.1×10 19 ~5.5×10 19 cm -3 ; The room temperature conductivity is 770~1553 S / cm; Thermal conductivity is 0.96 ~0.97 Wm -1 K -1 ; μ W / κ l The value is 0.059 ~ 0.15 m 3 KV -1 s -1 W -1 Thermoelectric figure of merit zT Not less than 1.0 in the range of 300 K ~ 400 K.

[0008] Preferably, when x=0 in the bismuth telluride-based thermoelectric material, it has the following properties: The carrier concentration at room temperature is 3.1×10 19 cm -3 ; The room temperature conductivity is 770 S / cm; Thermal conductivity is 0.96 Wm -1 K -1 ; Thermoelectric figure of merit zT 1.05 at 302 K; μ W / κ l The value is 0.059 m 3 KV -1 s -1 W -1 .

[0009] Preferably, when x=0.1 in the bismuth telluride-based thermoelectric material, it has the following properties: The carrier concentration at room temperature is 5.5×10 19 cm -3 ; The room temperature conductivity is 1553 S / cm; Thermal conductivity is 0.97 Wm -1 K -1 ; Thermoelectric figure of merit zT 1.33 at 395 K; μ W / κ l The value is 0.15 m 3 KV -1 s -1 W -1 .

[0010] Preferably, the three elements of bismuth, antimony and tellurium are evenly distributed in the bismuth telluride-based thermoelectric material, and the grain orientation is optimized through a hot extrusion process to form a densified microstructure.

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned bismuth telluride-based thermoelectric material, specifically comprising: Bi, Sb, Te and Cu2Se are weighed according to the stoichiometric ratio, mixed in a quartz glass tube, and then the quartz glass tube is sealed after evacuation. The quartz glass tube is then subjected to melt swinging, zone melting, crushing and pressing, hot extrusion molding and post-processing operations in sequence.

[0012] Preferably, the sealing includes sequentially using a vacuum pump and a molecular pump to perform a sealing operation, specifically, first turning on the vacuum pump to evacuate for 10 to 20 minutes and ensuring that the air pressure in the tube is less than 10.0 Pa, then turning on the molecular pump to further evacuate for 25 to 35 minutes until the pressure is less than 1.0 Pa, and then using an acetylene flame or an oxyhydrogen flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0013] Preferably, the melt swing is specifically as follows: melting at 730-750°C and keeping warm for 25-35 minutes, then swinging at 10-120 times / minute for 25-35 minutes; then moving the melt zone at a rate of 0.1-1.0 mm / minute at 715-725°C to form a pointed bottom cylindrical alloy ingot with a diameter of 13-20 mm.

[0014] Preferably, the crushing and pressing are specifically as follows: grinding the alloy ingot into 0.5-8 mm particles, placing the particles in a mold for hot pressing, preforming a hot extruded green body under a vacuum degree of <10 Pa, and then pressing it into a cylindrical green body with a diameter of 14-18 mm and a thickness of 18-20 mm under a uniaxial pressure of 45-65 MPa and a temperature of 400-430°C.

[0015] Preferably, the hot extrusion molding is specifically as follows: preheating the green body to 400-420° C., raising the temperature to 450-460° C. and applying a pressure of 55-65 MPa for extrusion.

[0016] More preferably, the diameter of the die inlet end is 14-18 mm, the extrusion ratio during the extrusion is 1.36-5.06, and the extrusion time is determined by the pressure and the amount of sample.

[0017] The extrusion process is as follows: The embryo is preheated at 400-430°C for 8-10 minutes without applying pressure. The temperature is then gradually raised to 450-480°C while gradually applying pressure to 55-65 MPa. Once the sample is extruded, heating is stopped and pressure is released.

[0018] Preferably, the post-processing includes removing uneven parts at the head and tail of the sample, and performing cutting and polishing.

[0019] A third aspect of the present invention provides an application of the bismuth telluride-based thermoelectric material described in the first aspect in a thermoelectric refrigerator or a thermoelectric generator.

[0020] The beneficial effects achieved by one or more technical solutions of the present invention are as follows: (1) The present invention significantly improves the thermoelectric figure of merit of the material by combining hot extrusion with Cu2Se doping ( zT The value is increased by 30%), among which bismuth (Bi), antimony (Sb), and tellurium (Te) are evenly distributed. The hot extrusion process optimizes the micro-grain structure and comprehensively improves the thermoelectric performance, making it suitable for industrial waste heat recovery and micro-refrigeration devices; The specific thermoelectric properties of bismuth telluride-based materials are as follows: 0.48 Sb 1.52 The bismuth, antimony, and tellurium elements are evenly distributed in the Te3+3 wt%Te sample (x = 0). The sample carriers are P-type carriers (both the Seebeck coefficient and the carrier concentration are positive), with a concentration of 3.1×10 19 cm -3 ; The Seebeck coefficient at room temperature is 204 μV K -1 ; Room temperature conductivity can reach 770 S / cm; room temperature power factor can reach 32 Wcm -1 K -2 ; Minimum thermal conductivity is 0.96 Wm -1 K -1 ; The minimum lattice thermal conductivity is 0.62 Wm -1 K -1 ; Maximum μ W / κ l The value is 0.059 m 3 KV -1 s -1 W -1 The comprehensive thermoelectric figure of merit can reach 1.05 at 302 K. After doping with 0.1 wt% Cu2Se (x = 0.1), the P-type carrier concentration of the sample is effectively increased to 5.5×10 19 cm -3 ; The Seebeck coefficient at room temperature is 155 μV K -1 ; Room temperature conductivity is effectively increased to 1553 S / cm; room temperature power factor is increased to 37 Wcm -1 K -2 ; Minimum thermal conductivity is 0.97 Wm -1 K -1 ; Maximum μ W / κ l The value is 0.15 m 3 KV -1 s -1 W -1 ; The comprehensive thermoelectric figure of merit can reach 1.33 at 395 K.

[0021] (2) Compared with the zone melting method, the material prepared by the hot extrusion method of the present invention is zT The value is higher than that of the zone melting method in a wide temperature range; compared with the hot pressing method, the material prepared by the hot extrusion method of the present invention has significantly improved electrical conductivity and power factor; compared with the hot pressing texturing method, the material prepared by the hot extrusion method of the present invention has lower thermal conductivity, and the overall zT The advantage of high value.

[0022] (3) The bismuth telluride dopant of the present invention can effectively increase the carrier concentration, significantly increase the electrical conductivity and power factor; and compared with the undoped Cu2Se sample, the lattice thermal conductivity of the doped Cu2Se sample is effectively suppressed; a higher μ W / κ l Value: Undoped Cu2Se sample: μ W / κ l = 0.053 m 3 KV -1 s -1 W -1 ; Cu2Se doped sample: μ W / κ l = 0.15 m 3 KV - 1 s -1 W -1 .

[0023] (4) The thermoelectric material prepared by the present invention has wide temperature range applicability and thermoelectric figure of merit ( zT ) maintains excellent performance in the range of 300 K~400 K: Undoped Cu2Se sample: zT ≥0.9 (300 ~400 K); Cu2Se-doped samples: zT ≥1.0 (300~400 K). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic cross-sectional view of the hot extrusion die in the preparation process of the present invention; Figure 2 The bulk X-ray diffraction pattern of the bismuth telluride-based thermoelectric material prepared in Examples 1 and 2 of the present invention; Figure 3 The scanning electron microscope morphology image and electron backscattered element distribution image of the bismuth telluride-based thermoelectric material prepared in Example 1 of the present invention; Figure 4 This is a curve showing the change in electrical conductivity of the bismuth telluride-based thermoelectric material prepared in Example 1 of the present invention as a function of temperature; Figure 5 This is a curve showing the Seebeck coefficient of the bismuth telluride-based thermoelectric material prepared in Example 1 of the present invention as a function of temperature; Figure 6 This is a curve showing the power factor of the bismuth telluride-based thermoelectric material prepared in Example 1 of the present invention as a function of temperature; Figure 7 This is a curve showing the change in thermal conductivity of the bismuth telluride-based thermoelectric material prepared in Example 1 of the present invention as a function of temperature; Figure 8 This is a curve showing the thermoelectric figure of merit of the bismuth telluride-based thermoelectric material prepared in Example 1 of the present invention as a function of temperature; Figure 9 This is a curve showing the change in electrical conductivity of the bismuth telluride-based thermoelectric material prepared in Example 2 of the present invention as a function of temperature; Figure 10 This is a curve showing the Seebeck coefficient of the bismuth telluride-based thermoelectric material prepared in Example 2 of the present invention as a function of temperature; Figure 11 This is a curve showing the power factor of the bismuth telluride-based thermoelectric material prepared in Example 2 of the present invention as a function of temperature; Figure 12 This is a curve showing the change in thermal conductivity of the bismuth telluride-based thermoelectric material prepared in Example 2 of the present invention as a function of temperature; Figure 13 This is a curve showing the change in thermoelectric figure of merit of the bismuth telluride-based thermoelectric material prepared in Example 2 of the present invention with temperature; Figure 14 The curves showing the change of electrical conductivity of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1 to 4 of the present invention with temperature; Figure 15 1 is a curve showing the change of the Seebeck coefficient of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1 to 4 of the present invention with temperature; Figure 16 The curves showing the power factor of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1 to 4 of the present invention as a function of temperature; Figure 17 1 is a curve showing the change in thermal conductivity of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1 to 4 of the present invention as a function of temperature; Figure 18 1 is a curve showing the change of lattice thermal conductivity of bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1 to 4 of the present invention with temperature; Figure 19 The graph shows the temperature-dependent thermoelectric figure of merit of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1 to 4 of the present invention. DETAILED DESCRIPTION

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0026] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0027] Example 1: In this embodiment, bismuth telluride-based thermoelectric material is prepared by hot extrusion method, and the chemical formula is Bi 0.48 Sb 1.52 Te3+3wt%Te; Preparation method: (1) Weigh 7.50620 g of bismuth, 13.84910 g of antimony, and 30.14475 g of tellurium with a purity of 99.999% and place them into a quartz glass tube with a diameter of 12.7 mm; turn on the vacuum pump to evacuate for 15 minutes and ensure that the air pressure in the tube is lower than 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0028] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750℃ to melt it, and keep it in this temperature zone for 30 minutes; then turn on the swing switch and swing it at a rate of 30 times per minute for 30 minutes; after the swinging is completed, turn off the swing switch; take out the 750℃ quartz glass tube while it is still hot, and place it vertically in a cooling barrel to cool naturally.

[0029] (3) The quartz glass tube is placed vertically in a zone melting furnace, and the melting temperature is set to 720°C; the melting zone moves from bottom to top through the sample ingot in the quartz glass tube at a speed of 0.5 mm / min; after cooling, a pointed-bottom cylindrical sample is finally obtained.

[0030] (4) Remove the zone-melted bismuth telluride alloy ingot from the completely cooled quartz tube, crush it in a mortar, and grind it for 30 minutes. Place the ground bismuth telluride particles into a graphite mold (16 mm in diameter). Place the graphite mold in a hot press furnace and insert a temperature probe into the mold. Turn on the vacuum pump and wait until the vacuum is <10 Pa before hot extruding the preform. Maintain the heat and pressure at 60 MPa uniaxial pressure and 420°C for 5 minutes to obtain a cylindrical blank with a diameter of 16 mm.

[0031] (5) Place the prefabricated blank on Figure 1 The hot extrusion process is shown in a graphite die with an inlet diameter of 16 mm and an outlet diameter of 10 mm. The die is then placed in a hot press furnace, and a temperature probe is inserted into the die. The vacuum pump is turned on, and after the vacuum reaches <10 Pa, hot extrusion of bismuth telluride is performed. This is done in two steps: 1) preheating the embryo at 420°C for 10 minutes without applying pressure; 2) gradually increasing the temperature to 460°C while applying pressure to 60 MPa.

[0032] (6) After the sample is extruded, stop heating and release the pressure. After the mold cools naturally, turn off the vacuum pump and remove the sample. After removing the uneven parts at the head and tail of the sample prepared by hot extrusion, cut and polish it for testing.

[0033] Example 2: In this embodiment, bismuth telluride-based thermoelectric material is prepared by hot extrusion method, and the chemical formula is Bi 0.48 Sb 1.52 Te3+3wt%Te+0.1 wt%Cu2Se; Preparation method: (1) Weigh 7.50620 g of bismuth with a purity of 99.999%, 13.84910 g of antimony, 30.14475 g of tellurium and 0.05150 g of Cu2Se, and put them into a quartz glass tube with a diameter of 12.7 mm; turn on the vacuum pump to evacuate for 15 minutes and ensure that the air pressure in the tube is lower than 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0034] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750℃ to melt it, and keep it in this temperature zone for 30 minutes; then turn on the swing switch and swing it at a rate of 30 times per minute for 30 minutes; after the swinging is completed, turn off the swing switch; take out the 750℃ quartz glass tube while it is still hot, and place it vertically in a cooling barrel to cool naturally.

[0035] (3) The quartz glass tube is placed vertically in a zone melting furnace, and the melting temperature is set to 720°C; the melting zone moves from bottom to top through the sample ingot in the quartz glass tube at a speed of 0.5 mm / min; after cooling, a pointed-bottom cylindrical sample is finally obtained.

[0036] (4) Remove the zone-melted bismuth telluride alloy ingot from the completely cooled quartz tube, crush it in a mortar, and grind it for 30 minutes. Place the ground bismuth telluride particles into a graphite mold (16 mm in diameter). Place the graphite mold in a hot press furnace and insert a temperature probe into the mold. Turn on the vacuum pump and wait until the vacuum is <10 Pa before hot extruding the preform. Maintain the heat and pressure at 60 MPa uniaxial pressure and 420°C for 5 minutes to obtain a cylindrical blank with a diameter of 16 mm.

[0037] (5) Place the prefabricated blank on Figure 1The diameter shown is a hot-extrusion graphite die with an inlet diameter of 16 mm and an outlet diameter of 10 mm. The die is then placed in a hot-pressing furnace, and a temperature probe is inserted into the die. The vacuum pump is turned on, and after the vacuum reaches <10 Pa, hot extrusion of bismuth telluride is performed. This is done in two steps: 1) preheating the embryo at 420°C for 10 minutes without applying pressure; 2) gradually increasing the temperature to 460°C while gradually applying pressure to 60 MPa.

[0038] (6) After the sample is extruded, stop heating and release the pressure. After the mold cools naturally, turn off the vacuum pump and remove the sample. After removing the uneven parts at the head and tail of the sample prepared by hot extrusion, cut and polish it for testing.

[0039] Comparative Example 1: In this comparative example, bismuth telluride-based thermoelectric material was prepared by zone melting method, and the chemical formula is Bi 0.48 Sb 1.52 Te3+3wt%Te; Preparation method: (1) Weigh 7.50620 g of bismuth, 13.84910 g of antimony, and 30.14475 g of tellurium with a purity of 99.999% and place them into a quartz glass tube with a diameter of 12.7 mm; turn on the vacuum pump to evacuate for 15 minutes and ensure that the air pressure in the tube is lower than 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0040] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750℃ to melt it, and keep it in this temperature zone for 30 minutes; then turn on the swing switch and swing it at a rate of 30 times per minute for 30 minutes; after the swinging is completed, turn off the swing switch; take out the 750℃ quartz glass tube while it is still hot, and place it vertically in a cooling barrel to cool naturally.

[0041] (3) The quartz glass tube is placed vertically in a zone melting furnace, and the melting temperature is set to 720°C; the melting zone moves from bottom to top through the sample ingot in the quartz glass tube at a speed of 0.5 mm / min; after cooling, a pointed-bottom cylindrical sample is finally obtained.

[0042] (4) After removing the uneven parts at the head and tail of the sample prepared by zone melting, cut and polish it for testing.

[0043] Comparative Example 2: In this comparative example, bismuth telluride-based thermoelectric material was prepared by hot pressing, and the chemical formula is Bi 0.48 Sb 1.52 Te3+3wt%Te; Preparation method: (1) Weigh 7.50620 g of bismuth, 13.84910 g of antimony, and 30.14475 g of tellurium with a purity of 99.999% and place them into a quartz glass tube with a diameter of 12.7 mm; turn on the vacuum pump to evacuate for 15 minutes and ensure that the air pressure in the tube is lower than 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0044] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750℃ to melt it, and keep it in this temperature zone for 30 minutes; then turn on the swing switch and swing it at a rate of 30 times per minute for 30 minutes; after the swinging is completed, turn off the swing switch; take out the 750℃ quartz glass tube while it is still hot, and place it vertically in a cooling barrel to cool naturally.

[0045] (3) The quartz glass tube is placed vertically in a zone melting furnace, and the melting temperature is set to 720°C; the melting zone moves from bottom to top through the sample ingot in the quartz glass tube at a speed of 0.5 mm / min; after cooling, a pointed-bottom cylindrical sample is finally obtained.

[0046] (4) Remove the zone-melted bismuth telluride alloy ingot from the completely cooled quartz tube, crush it in a mortar, and grind it for 30 minutes. Place the ground bismuth telluride particles into a hot-pressed graphite mold with a diameter of 10 mm. Then place the mold in a hot-pressing furnace and insert a temperature probe into the mold. Turn on the vacuum pump and wait until the vacuum is <10 Pa before hot-pressing the bismuth telluride. The specific steps are as follows: gradually increase the temperature and pressure to 420°C and 60 MPa.

[0047] (5) After 10 minutes of heat and pressure maintenance, stop heating; after the mold cools naturally, release the pressure, turn off the vacuum pump and remove the sample. Obtain the hot pressed sample, cut and polish it for testing.

[0048] Comparative Example 3: In this comparative example, bismuth telluride samples were prepared by hot pressing and texturing method, and the chemical formula is Bi 0.48 Sb 1.52 Te3+3wt%Te; Preparation method: (1) Weigh 7.50620 g of bismuth, 13.84910 g of antimony, and 30.14475 g of tellurium with a purity of 99.999% and place them into a quartz glass tube with a diameter of 12.7 mm; turn on the vacuum pump to evacuate for 15 minutes and ensure that the air pressure in the tube is lower than 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0049] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750℃ to melt it, and keep it in this temperature zone for 30 minutes; then turn on the swing switch and swing it at a rate of 30 times per minute for 30 minutes; after the swinging is completed, turn off the swing switch; take out the 750℃ quartz glass tube while it is still hot, and place it vertically in a cooling barrel to cool naturally.

[0050] (3) The quartz glass tube is placed vertically in a zone melting furnace, and the melting temperature is set to 720°C; the melting zone moves from bottom to top through the sample ingot in the quartz glass tube at a speed of 0.5 mm / min; after cooling, a pointed-bottom cylindrical sample is finally obtained.

[0051] (4) The zone-melted bismuth telluride alloy ingot was removed from the completely cooled quartz tube and crushed and ground in a mortar for 30 minutes. The ground bismuth telluride particles were placed in a metal mold (10 mm diameter). The metal mold was placed in a hydraulic press and pressed into a cylindrical body with a diameter of 10 mm under a uniaxial pressure of 20 MPa.

[0052] (5) Place the prefabricated body in a hot-pressed graphite mold with a diameter of 16 mm. Then place the mold in a hot-pressing furnace and insert a temperature probe into the mold. Turn on the vacuum pump and wait until the vacuum degree is <10 Pa before hot-pressing the bismuth telluride texture. This is done in two steps: 1) Preheat the body at 420°C for 10 minutes without applying pressure; 2) Gradually increase the temperature to 460°C while gradually applying pressure to 60 MPa and maintain this temperature and pressure for 10 minutes.

[0053] (6) After the sample is hot-pressed and textured, stop heating and release the pressure. After the mold cools naturally, turn off the vacuum pump and remove the sample. The sample prepared by hot-pressing and textured is cut and polished for testing.

[0054] Comparative Example 4: This comparative example provides a bismuth telluride-based thermoelectric material and a preparation method thereof, the chemical formula of which is Bi 0.48 Sb 1.52 Te3+3wt%Te+0.1 wt% Cu2Se; Preparation method: (1) Weigh 7.50620 g of bismuth with a purity of 99.999%, 13.84910 g of antimony, 30.14475 g of tellurium and 0.05150 g of Cu2Se, and put them into a quartz glass tube with a diameter of 12.7 mm; turn on the vacuum pump to evacuate for 15 minutes and ensure that the air pressure in the tube is lower than 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0055] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750℃ to melt it, and keep it in this temperature zone for 30 minutes; then turn on the swing switch and swing it at a rate of 30 times per minute for 30 minutes; after the swinging is completed, turn off the swing switch; take out the 750℃ quartz glass tube while it is still hot, and place it vertically in a cooling barrel to cool naturally.

[0056] (3) The quartz glass tube is placed vertically in a zone melting furnace, and the melting temperature is set to 720°C; the melting zone moves from bottom to top through the sample ingot in the quartz glass tube at a speed of 0.5 mm / min; after cooling, a pointed-bottom cylindrical sample is finally obtained.

[0057] (4) Take out the zone-melted bismuth telluride alloy ingot from the completely cooled quartz tube and remove the head and tail. Place the alloy ingot into a graphite mold (16 mm in diameter) (no crushing or grinding operations). Then place the mold into a hot press furnace and insert the temperature probe into the mold. Turn on the vacuum pump and press the bismuth telluride after the vacuum degree is <10 Pa. It is divided into two steps: 1) Preheat at 420℃ for 30 minutes without applying pressure during this period to complete the preheating of the embryo; 2) Gradually increase the temperature to 460℃ while gradually applying pressure to 60 MPa and keep the temperature and pressure for 300 minutes.

[0058] (5) Place the prefabricated blank in a hot extrusion graphite die with an inlet diameter of 16 mm and an outlet diameter of 10 mm. The die structure is as follows: Figure 1 The mold is then placed in a hot press furnace, and a temperature probe is inserted into the mold. The vacuum pump is turned on, and after the vacuum reaches <10 Pa, hot extrusion of the bismuth telluride is performed. This is done in two steps: 1) preheating the blank at 420°C for 10 minutes without applying pressure; 2) gradually increasing the temperature to 460°C while applying pressure to 60 MPa.

[0059] (6) After the sample is extruded, stop heating and release the pressure. After the mold cools naturally, turn off the vacuum pump and remove the sample. After removing the uneven parts at the head and tail of the sample prepared by hot extrusion, cut and polish it for testing.

[0060] Experimental Example 1: This experimental example tests the structural characteristics and performance of Examples 1-2 and Comparative Examples 1-4. (1) Structural features: like Figure 2 As shown, the X-ray diffraction pattern (XRD) shows that Bi 0.48 Sb 1.52The X-ray diffraction peaks of the Te3 sample and the standard X-ray diffraction pattern of the bismuth telluride-based sample show that the sample prepared in Example 1 is a pure-phase bismuth telluride material with no impurity peaks. Similarly, after Cu2Se doping, the XRD diffraction peaks of the sample prepared in Example 2 also conform to the standard spectrum of bismuth telluride, without Cu2Se peaks. The difference is that the peak position of the diffraction peak of the sample does shift toward a lower angle after Cu2Se doping. This is because the incorporation of Cu2Se into the bismuth telluride lattice causes an increase in its unit cell parameters.

[0061] like Figure 3 As shown in the scanning electron microscope morphology diagram and electron backscatter diffraction element distribution diagram, the Bi prepared by hot extrusion method in Example 1 of the present invention is 0.48 Sb 1.52 The elements of the Te3 sample are evenly distributed and there is no second phase, which is consistent with the XRD results. In addition, the polished surface of the sample is dense and free of holes.

[0062] (2) Performance testing: The performance tests of the samples obtained in the embodiments of the present invention and the comparative examples are divided into two parts: electrical performance and thermal performance. Among them, electrical conductivity, Seebeck coefficient, and power factor belong to electrical performance, which are directly tested by the ZEM equipment produced by Riko in Japan. Specifically, a diamond wire cutting machine is used to cut the sample into a 3*3*12 mm rectangular parallelepiped, which is placed in the ZEM, and the test temperature points are set to 30, 80, 130, 180, and 230°C to complete the characterization of the electrical performance. The diamond wire cutting machine is then used to cut the sample into 10*10*1.5 mm square pieces, and the thermal conductivity is tested with the help of a laser thermal conductivity meter LFA produced in Germany. The temperature setting is the same as that of the electrical test. Finally, μ is calculated based on the electrical and thermal properties. W / κ l Value and zT value.

[0063] 1) Conductivity test: like Figure 4 、 Figure 9 As shown in the figure, the conductivity of the samples prepared in Examples 1 and 2 gradually decreases with the increase of temperature, showing a metallic conductive behavior. 0.48 Sb 1.52 The room temperature conductivity of the Te3 sample is 770 S cm -1 , the highest temperature conductivity is 351 S cm -1 The electrical conductivity of the Cu2Se-doped sample was significantly improved in the whole temperature range, with the room temperature conductivity and the highest temperature conductivity being 1553 and 590 S cm, respectively. -1 .like Figure 14 As shown, the room temperature conductivity of the samples prepared in Comparative Examples 1 to 4 were 1137, 642, 866, and 1587 S cm, respectively.-1 The highest temperature conductivity is 536, 371, 391 and 611 S cm -1 .

[0064] 2) Seebeck coefficient test: like Figure 5 、 Figure 10 As shown, Bi before and after Cu2Se doping 0.48 Sb 1.52 The Seebeck coefficient of Te3 samples (samples prepared in Examples 1 and 2) varies with temperature, but is always positive, indicating that it is a P-type material. 0.48 Sb 1.52 The Seebeck value of Te3 sample reaches a maximum value of 204 μVK near room temperature. -1 As the temperature increases, the Seebeck coefficient gradually decreases to 180 μVK -1 After Cu2Se doping, the Seebeck coefficient of the sample prepared in Example 2 is significantly reduced and presents a parabolic change trend, that is, its Seebeck coefficient decreases from 155 μVK -1 As the temperature gradually increases, it reaches a maximum value of 191 μVK near 445 K. -1 , and then gradually decreased to 184 μVK with increasing temperature. -1 .like Figure 15 As shown in FIG1 , the room temperature Seebeck coefficients of the samples prepared in Comparative Examples 1 to 4 are 204, 229, 215 and 170 μVK, respectively. -1 , the highest SeeBeck coefficients are 222, 240, 237 and 202 μVK -1 .

[0065] 3) Power factor test: like Figure 6 、 Figure 11 As shown, based on the formula PF = σS 2 The power factor of the sample at the corresponding temperature can be calculated using the conductivity and Seebeck coefficient measured by ZEM. Although the Seebeck coefficient of the sample prepared in Example 2 is significantly reduced after Cu2Se doping, the greatly improved conductivity still achieves an improvement in the power factor of the sample. After doping, the room temperature power factor can reach 37μWcm -1 K -2 , the highest temperature can reach 20 μWcm -1 K -2 Higher than the undoped sample obtained in Example 1 (room temperature power factor of 32 μWcm -1 K -2, the highest temperature is 11 μWcm -1 K -2 ).like Figure 16 As shown in Figure 2, the room temperature power factors of the samples prepared in Comparative Examples 1 to 4 are 47, 34, 40, and 46 μWcm, respectively. -1 K -2 The power factors at the highest temperature are 16, 11, 13 and 23 μWcm respectively. -1 K -2 .

[0066] 4) Thermal conductivity and lattice thermal conductivity test: like Figure 7 、 Figure 12 As shown, the thermal conductivity of the sample was obtained based on the LFA device, and then the lattice thermal conductivity of the sample was calculated according to the formula, κ l = κ – κ e , κ e = LσT ,in κ e is the electronic thermal conductivity, L is the Lorentz constant, which is calculated from the Seebeck coefficient of the sample. Figure 7 As shown, Bi 0.48 Sb 1.52 The lowest thermal conductivity and lattice thermal conductivity of Te3 sample are about 0.96 and 0.62 Wm -1 K -1 After Cu2Se doping, the lowest total thermal conductivity of the sample increased slightly to 0.97 Wm -1 K -1 , which is related to the improvement of electronic thermal conductivity caused by the greatly increased electrical conductivity. Nevertheless, the lattice thermal conductivity after Cu2Se doping is effectively reduced to 0.28 Wm -1 K -1 , effectively reducing the lattice thermal conductivity of bismuth telluride. Figure 17 、 18 As shown in Figure 2, the lowest thermal conductivity and lowest lattice thermal conductivity of the samples prepared in Comparative Examples 1 to 4 are 1.50, 1.14, 1.32, and 1.31 Wm, respectively. -1 K -1 and 1.00, 0.83, 0.95, and 0.63 Wm -1 K -1 .

[0067] 5) μ W / κ l test: As shown in Table 1, based on the electrical and thermal properties measured above, using μ W / κ l Calculation formula μ W / κ l = 3h 3 σ[exp[|S|e / k B -2] / [1+exp[-5(e|S| / k B -1)]]+(3 / π 2 )(|S|e / k B ) / [1+exp[5(e|S| / k B -1)]]] / [8πe(2m e k B T) 3 / 2 κ l ], where h, π, and m e , K B and e are Planck constant, pi, electron mass, Boltzmann constant and electron charge respectively, and the μ of the sample is calculated W / κ l value.

[0068] By calculating the μm of the bismuth telluride sample prepared by the hot extrusion process in Example 1 W / κ l The value is 0.059 m 3 KV -1 s -1 W -1 , which is better than the samples prepared by other strategies (μ W / κ l The values ​​are 0.053, 0.049 and 0.051 m 3 KV -1 s -1 W -1 ). Thanks to Cu2Se doping, μ W / κ l The value is increased to 0.15 m 3 KV -1 s -1 W -1 Better than the sample prepared by the strategy of Comparative Example 4 (μ W / κ l The value is 0.074 m 3 KV -1 s -1 W -1 ).

[0069] Table 1

[0070] 6) Thermoelectric figure of merit test: like Figure 8 、 Figure 13 、 Figure 19 As shown, based on the electrical and thermal properties measured above, the thermoelectric figure of merit is calculated using the formula zT = PFT / κ , the thermoelectric figure of merit of the sample is calculated. W / κ l The value is greatly improved, and its thermoelectric performance is significantly optimized. zT The value is 1.33. It is 27% higher than the 1.05 of the undoped sample; it is 36%, 49%, 38% and 15% higher than the samples prepared in Comparative Examples 1 to 4 (the zT The values ​​are 0.98, 0.89, 0.96, and 1.16 respectively) 7) Room temperature P-type carrier concentration, effective carrier mass and mobility test: As shown in Tables 2 and 3, the carrier concentrations of the samples prepared in Examples 1 and 2 of the present invention are all positive, that is, P-type materials, wherein the carrier concentration after Cu2Se doping is 5.5×10 19 cm -3 , which is significantly higher than the carrier concentration of undoped (3.1×10 19 cm -3 Based on the carrier concentration and Seebeck coefficient, theoretical calculations show that the effective carrier mass of the Cu2Se-doped sample is 0.93 m0, which is lower than that of the undoped sample, which helps to improve the mobility of the material.

[0071] The test results further confirmed this. The mobility of the Cu2Se doped sample was 176.8 cm 2 V -1 s -1 , which is higher than the undoped 156.8 cm 2 V -1 s -1 The increased carrier concentration and enhanced mobility together improve the conductivity of the sample.

[0072] Table 2

[0073] Table 3

[0074] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A bismuth telluride-based thermoelectric material, characterized in that: The chemical composition of the thermoelectric material is: Bi 0.48 Sb 1.52 Te3+3wt%Te+ x wt% Cu2Se, Wherein, 0≤x≤0.1, and the material has at least one of the following properties: The carrier concentration at room temperature is 3.1×10 19 ~5.5×10 19 cm -3 ; The room temperature conductivity is 770~1553 S / cm; Thermal conductivity is 0.96 ~0.97 Wm -1 K -1 ; μ W / κ l The value is 0.059 ~ 0.15 m 3 KV -1 s -1 W -1 Thermoelectric figure of merit zT Not less than 1.0 in the range of 300 K ~ 400 K.

2. The bismuth telluride-based thermoelectric material according to claim 1, wherein When x=0 in the bismuth telluride-based thermoelectric material, it has the following properties: The carrier concentration at room temperature is 3.1×10 19 cm -3 ; The room temperature conductivity is 770 S / cm; Thermal conductivity is 0.96 Wm -1 K -1 ; Thermoelectric figure of merit zT 1.05 at 302 K; μ W / κ l The value is 0.059 m 3 KV -1 s -1 W -1 .

3. The bismuth telluride-based thermoelectric material according to claim 2, wherein: When x=0.1 in the bismuth telluride-based thermoelectric material, it has the following properties: The carrier concentration at room temperature is 5.5×10 19 cm -3 ; The room temperature conductivity is 1553 S / cm; Thermal conductivity is 0.97 Wm -1 K -1 ; Thermoelectric figure of merit zT 1.33 at 395 K; μ W / κ l The value is 0.15 m 3 KV -1 s -1 W -1 .

4. The bismuth telluride-based thermoelectric material according to claim 1, wherein The three elements of bismuth, antimony and tellurium are evenly distributed in the bismuth telluride-based thermoelectric material, and the grain orientation is optimized through a hot extrusion process to form a densified microstructure.

5. A method for preparing a bismuth telluride-based thermoelectric material according to any one of claims 1 to 4, characterized in that: Bi, Sb, Te and Cu2Se are weighed according to the stoichiometric ratio, mixed in a quartz glass tube, and then the quartz glass tube is sealed after evacuation. The quartz glass tube is then subjected to melt swinging, zone melting, crushing and pressing, hot extrusion molding and post-processing operations in sequence.

6. The preparation method according to claim 5, wherein The sealing includes sequentially using a vacuum pump and a molecular pump to perform a sealing operation. Specifically, the vacuum pump is first turned on to evacuate for 10 to 20 minutes and ensure that the air pressure in the tube is less than 10.0 Pa. The molecular pump is then turned on to further evacuate for 25 to 35 minutes until the pressure is less than 1.0 Pa. An acetylene flame or an oxyhydrogen flame is then used to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

7. The preparation method according to claim 5, wherein The melt rocking is specifically as follows: melting at 730-750°C and keeping the temperature for 25-35 minutes, then rocking at 10-120 times / minute for 25-35 minutes; then moving the melt zone at a rate of 0.1-1.0 mm / minute at 715-725°C to form a pointed-bottom cylindrical alloy ingot with a diameter of 13-20 mm.

8. The preparation method according to claim 5, wherein The crushing and pressing are specifically as follows: grinding the alloy ingot into 0.5-8 mm particles, placing the particles in a mold for hot pressing, preforming a hot extrusion embryo under a vacuum degree of <10 Pa, and then pressing it into a cylindrical embryo with a diameter of 14-18 mm and a thickness of 18-20 mm under a uniaxial pressure of 45-65 MPa and a temperature of 400-430°C.

9. The preparation method according to claim 5, wherein The hot extrusion molding is specifically as follows: after preheating the blank to 400-420°C, the temperature is increased to 450-460°C and a pressure of 55-65 MPa is applied for extrusion; wherein, the diameter of the die inlet end is 14-18 mm, and the extrusion ratio during the extrusion is 1.36-5.06; the extrusion process is specifically as follows: first preheating at 400-430°C for 8-10 minutes without applying pressure during the preheating of the blank; then gradually increasing the temperature to 450-480°C while gradually applying a pressure of 55-65 MPa; after the sample is extruded, stopping heating and releasing the pressure; The post-processing includes removing the uneven parts at the head and tail of the sample, and performing cutting and polishing.

10. Use of the bismuth telluride-based thermoelectric material according to any one of claims 1 to 4 in a thermoelectric refrigerator.

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