A bismuth telluride-based thermoelectric material, its preparation method and application

Abstract

This invention belongs to the field of thermoelectric semiconductor materials technology, and relates to a bismuth telluride-based thermoelectric material, its preparation method, and its application. This invention obtains Bii through processes such as melt tumbling, zone melting, crushing and pressing, and hot extrusion molding. 0.48 Sb 1.52 Te3+3 wt%Te+ x wt% Cu₂Se, 0≤x≤0.1, has a room temperature carrier concentration of (3.1~5.5)×10⁻⁶. 19 cm ‑3 Electrical conductivity at room temperature is 770~1553 S / cm; thermal conductivity is 0.96~0.97 W / m². ‑1 K ‑1 μ W / k l The value is 0.15 m 3 KV ‑1 s ‑1 W ‑1 Thermoelectric figure of merit zT Not less than 1.0 (300~400 K). Specifically, it is produced by combining hot extrusion with Cu2Se doping. The hot extrusion process is used to optimize the grain orientation, form a dense microstructure, and reduce the thermal resistance of grain boundaries. It is suitable for industrial waste heat recovery and micro-refrigeration devices.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric semiconductor materials technology, specifically relating to a bismuth telluride-based thermoelectric material, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Based on the Seebeck and Peltier effects, thermoelectric materials enable the direct conversion between thermal and electrical energy, showing significant application potential in areas such as low-quality waste heat recovery, waste heat recycling, and precise temperature control. The performance of thermoelectric materials is determined by their thermoelectric figure of merit. zT The measure, its expression is zT = σS 2 T / κ .in, σ, S, T, κ and σS 2 These are electrical conductivity, Seebeck coefficient, absolute temperature, thermal conductivity, and power factor ( ). PF = σS 2 Its advantages and disadvantages can be determined by its weight-average mobility μ. W measure). κ Electronic thermal conductivity dominated by charge carriers ( κ e ) and lattice thermal conductivity dominated by lattice vibrations ( κ l ).However, σ, S and κ e Because the charge carriers and electronic band structure are coupled together, it is difficult to achieve a synergistic improvement in all three parameters; the difference is that... κ l Relatively independent. Therefore, μ W / κ l The ratio can be used to measure the quality of thermoelectric performance.

[0004] Bismuth telluride-based materials with layered structures exhibit excellent thermoelectric properties, enabling significant applications in near-room temperature power generation and refrigeration. This layered structure also endows bismuth telluride with extremely strong anisotropy in thermoelectric transport characteristics. Currently, most commercially available bismuth telluride materials are prepared using zone melting methods. Bismuth telluride crystals prepared by this method possess extremely high orientation and power factor. However, high crystal orientation is accompanied by extremely high thermal conductivity. As can be seen from the thermoelectric figure of merit calculation formula, high thermal conductivity partially offsets the effect of high power factor on the thermoelectric figure of merit, which limits the thermoelectric performance of bismuth telluride materials prepared by zone melting. Existing techniques such as vacuum hot pressing, hot deformation, and hot pressing textured methods effectively reduce the thermal conductivity of the materials, but their electrical properties are still lower than those of zone-melted samples, indicating that their overall thermoelectric performance still needs improvement.

[0005] Furthermore, while existing technologies can effectively control the carrier concentration of materials through doping compounds, the coupling phenomenon between carriers and electronic band structures makes it difficult to achieve synergistic improvements in multiple parameters (such as electrical conductivity, thermal conductivity, and Seebeck coefficient), thus hindering significant enhancements in thermoelectric performance. Therefore, those skilled in the art urgently need to develop a bismuth telluride thermoelectric material with superior thermoelectric properties. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a bismuth telluride-based thermoelectric material, its preparation method, and its applications. Specifically, the bismuth telluride-based thermoelectric material prepared in this application achieves high electrical performance and low thermal conductivity, i.e., high μ-coefficient, through optimization of material composition and process parameters. W / κ l The value was increased, and the thermoelectric figure of merit was significantly improved.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a bismuth telluride-based thermoelectric material, 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:

[0009] The carrier concentration at room temperature is 3.1 × 10⁻⁶. 19 ~5.5×10 19 cm -3 ;

[0010] The room temperature conductivity is 770~1553 S / cm;

[0011] Thermal conductivity is 0.96 ~ 0.97 W / m.-1 K -1 ;

[0012] μ W / κ l The value is 0.059 ~ 0.15 m 3 KV -1 s -1 W -1

[0013] Thermoelectric figure of merit zT Not less than 1.0 in the range of 300 K to 400 K.

[0014] Preferably, when x=0, the bismuth telluride-based thermoelectric material has the following properties:

[0015] The carrier concentration at room temperature is 3.1 × 10⁻⁶. 19 cm -3 ;

[0016] The room temperature conductivity is 770 S / cm;

[0017] Thermal conductivity is 0.96 W / m -1 K -1 ;

[0018] Thermoelectric figure of merit zT It reaches 1.05 at 302 K;

[0019] μ W / κ l The value is 0.059 m 3 KV -1 s -1 W -1 .

[0020] Preferably, the bismuth telluride-based thermoelectric material, when x=0.1, has the following properties:

[0021] The carrier concentration at room temperature is 5.5 × 10⁻⁶. 19 cm -3 ;

[0022] The electrical conductivity at room temperature is 1553 S / cm;

[0023] Thermal conductivity is 0.97 W / m -1 K -1 ;

[0024] Thermoelectric figure of merit zT It reaches 1.33 at 395 K;

[0025] μ W / κ lThe value is 0.15 m 3 KV -1 s -1 W -1 .

[0026] Preferably, the bismuth, antimony, and tellurium elements in the bismuth telluride-based thermoelectric material are uniformly distributed, and the grain orientation is optimized through a hot extrusion process to form a dense microstructure.

[0027] A second aspect of the present invention provides a method for preparing the above-mentioned bismuth telluride-based thermoelectric material, specifically comprising:

[0028] Bi, Sb, Te and Cu2Se are weighed according to stoichiometric ratio, and the raw materials are mixed in a quartz glass tube. After vacuuming, the quartz glass tube is sealed, and the processes of melting and shaking, zone melting, crushing and pressing, hot extrusion molding and post-processing are carried out in sequence.

[0029] Preferably, the sealing process includes sequentially using a vacuum pump and a molecular pump for sealing operations. Specifically, first, the vacuum pump is turned on to evacuate the air for 10-20 minutes and ensure that the air pressure inside the tube is less than 10.0 Pa. Then, the molecular pump is turned on to further evacuate the air for 25-35 minutes until the pressure is less than 1.0 Pa. Finally, an acetylene flame or an oxyhydrogen flame is used to heat the quartz glass tube rotating along the axial direction until the quartz glass tube is sealed.

[0030] Preferably, the melting and oscillating process specifically involves: melting at 730~750℃ and holding for 25~35 minutes, then oscillating at 10~120 times / minute for 25~35 minutes; subsequently moving the molten zone at 715~725℃ at a rate of 0.1~1.0 mm / minute to form a pointed-bottom cylindrical alloy ingot with a diameter of 13~20 mm.

[0031] Preferably, the crushing and pressing specifically involves: grinding the alloy ingot into 0.5~8 mm particles, placing the particles in a mold for hot pressing, pre-forming the hot extrusion blank under a vacuum degree <10 Pa, and then pressing it into a cylindrical blank 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℃.

[0032] Preferably, the hot extrusion molding specifically involves: preheating the billet to 400~420°C, then raising the temperature to 450~460°C and applying a pressure of 55~65 MPa for extrusion.

[0033] More preferably, the diameter of the mold inlet is 14-18 mm, the extrusion ratio during extrusion is 1.36-5.06, and the extrusion time is determined by the pressure and the amount of sample.

[0034] The extrusion process is as follows: first, preheat the sample at 400~430℃ for 8~10 minutes without applying pressure to complete the preheating of the preform; then gradually increase the temperature to 450~480℃ while gradually applying pressure to 55~65 MPa. After the sample extrusion is completed, stop heating and release the pressure.

[0035] Preferably, the post-processing includes removing uneven portions at the beginning and end of the sample, as well as cutting and polishing.

[0036] A third aspect of the present invention provides an application of the bismuth telluride-based thermoelectric material described in the first aspect in thermoelectric coolers and thermoelectric generators.

[0037] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0038] (1) This 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 them, the three elements of 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.

[0039] The specific thermoelectric properties of bismuth telluride-based materials are as follows: Bi 0.48 Sb 1.52 The Te3+3 wt%Te sample (x = 0) exhibits a uniform distribution of bismuth, antimony, and tellurium; the sample carries p-type charge carriers (both the Seebeck coefficient and carrier concentration are positive), with a concentration of 3.1 × 10⁻⁶. 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 The lowest thermal conductivity is 0.96 W / m². -1 K -1 The lowest lattice thermal conductivity is 0.62 W / m. -1 K -1 Maximum μ W / κ l The value is 0.059 m 3 KV -1 s -1 W -1 The overall thermoelectric figure of merit can reach 1.05 at 302 K;

[0040] After doping with 0.1 wt% Cu₂Se (x = 0.1), the p-type carrier concentration of the sample was effectively increased to 5.5 × 10⁻⁶. 19 cm-3 The Seebeck coefficient at room temperature is 155 μV K. -1 Room temperature conductivity can be effectively increased to 1553 S / cm; room temperature power factor is increased to 37 Wcm. -1 K -2 The lowest thermal conductivity is 0.97 W / m². -1 K -1 Maximum μ W / κ l The value is 0.15 m 3 KV -1 s -1 W -1 The overall thermoelectric figure of merit can reach 1.33 at 395 K.

[0041] (2) Compared with zone melting, the material prepared by hot extrusion in this invention is... zT The electrical conductivity and power factor are higher over a wide temperature range than those obtained by zone melting; compared to hot pressing, the materials prepared by the hot extrusion method of this invention exhibit significantly improved electrical conductivity and power factor; compared to hot pressing texturing, the materials prepared by the hot extrusion method of this invention have lower thermal conductivity, resulting in better overall performance. zT The advantage of high value.

[0042] (3) The bismuth telluride dopant involved in this invention can effectively increase the carrier concentration and significantly increase the conductivity and power factor; and compared with the undoped Cu2Se sample, the lattice thermal conductivity of the doped Cu2Se sample is effectively suppressed; achieving 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 .

[0043] (4) The thermoelectric material prepared by this invention has wide temperature range applicability and a thermoelectric figure of merit ( ). zT Excellent performance is maintained in the 300 K~400 K range: Undoped Cu2Se sample: zT ≥0.9 (300 ~400 K); Cu2Se doped sample: zT ≥1.0 (300~400 K). Attached Figure Description

[0044] Figure 1 This is a schematic cross-sectional view of the hot extrusion die used in the preparation process of this invention;

[0045] Figure 2 The bulk X-ray diffraction patterns of the bismuth telluride-based thermoelectric materials prepared in Examples 1-2 of this invention are shown below.

[0046] Figure 3 The images show the scanning electron microscope morphology and electron backscattering elemental distribution of the bismuth telluride-based thermoelectric material prepared in Example 1 of this invention.

[0047] Figure 4 The curve showing the change in electrical conductivity as a function of temperature for the bismuth telluride-based thermoelectric material prepared in Example 1 of this invention;

[0048] Figure 5 The curve showing the Seebeck coefficient of the bismuth telluride-based thermoelectric material prepared in Example 1 of this invention as a function of temperature.

[0049] Figure 6 The curve showing the power factor of the bismuth telluride-based thermoelectric material prepared in Example 1 of this invention as a function of temperature.

[0050] Figure 7 The curve showing the change in thermal conductivity of the bismuth telluride-based thermoelectric material prepared in Example 1 of this invention as a function of temperature.

[0051] Figure 8 The curve showing the thermoelectric figure of merit as a function of temperature for the bismuth telluride-based thermoelectric material prepared in Example 1 of this invention;

[0052] Figure 9 The curve showing the change in electrical conductivity as a function of temperature for the bismuth telluride-based thermoelectric material prepared in Example 2 of this invention;

[0053] Figure 10 The curve showing the Seebeck coefficient of the bismuth telluride-based thermoelectric material prepared in Example 2 of this invention as a function of temperature;

[0054] Figure 11 The curve showing the power factor of the bismuth telluride-based thermoelectric material prepared in Example 2 of this invention as a function of temperature.

[0055] Figure 12 The curve showing the change in thermal conductivity of the bismuth telluride-based thermoelectric material prepared in Example 2 of this invention as a function of temperature.

[0056] Figure 13 The curve showing the thermoelectric figure of merit as a function of temperature for the bismuth telluride-based thermoelectric material prepared in Example 2 of this invention;

[0057] Figure 14 The curves show the electrical conductivity of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1-4 of this invention as a function of temperature.

[0058] Figure 15 The curves showing the Seebeck coefficient of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1-4 of this invention as a function of temperature are shown.

[0059] Figure 16 The curves show the power factor of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1-4 of this invention as a function of temperature.

[0060] Figure 17 The curves show the thermal conductivity of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1-4 of this invention as a function of temperature.

[0061] Figure 18 The curves show the lattice thermal conductivity of the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1-4 of this invention as a function of temperature.

[0062] Figure 19 The curves show the thermoelectric figure of merit as a function of temperature for the bismuth telluride-based thermoelectric materials prepared in Comparative Examples 1-4 of this invention. Detailed Implementation

[0063] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0064] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0065] Example 1:

[0066] This embodiment prepares bismuth telluride-based thermoelectric materials via hot extrusion, with the chemical formula Bi. 0.48 Sb 1.52 Te3+3wt%Te;

[0067] Preparation method: (1) Weigh 7.50620 g of bismuth with a purity of 99.999%, 13.84910 g of antimony and 30.14475 g of tellurium 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 below 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use an acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0068] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750°C to melt, and keep it at this temperature for 30 minutes; then turn on the swing switch and swing at a rate of 30 times per minute for 30 minutes; after the swing is finished, turn off the swing switch; take out the quartz glass tube at 750°C while it is still hot, and place it vertically in a cooling tank to cool naturally.

[0069] (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.

[0070] (4) Remove the molten bismuth telluride alloy ingot from the completely cooled quartz tube and crush and grind it in a mortar for 30 minutes. Load 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 pre-form the hot extrusion blank after the vacuum degree is <10 Pa. Hold the blank at 60 MPa uniaxial pressure and 420°C for 5 minutes to obtain a cylindrical blank with a diameter of 16 mm.

[0071] (5) Place the precast blank in a position such as Figure 1 The sample is placed in a hot-extruded graphite mold with an inlet diameter of 16 mm and an outlet diameter of 10 mm. The mold is then placed in a hot-press furnace, and a temperature probe is inserted. The vacuum pump is turned on, and after the vacuum level is <10 Pa, hot extrusion preparation of bismuth telluride is carried out. This process consists of two steps: 1) Preheating at 420℃ for 10 minutes without applying pressure to complete the preheating of the preform; 2) Gradually increasing the temperature to 460℃ while simultaneously gradually applying pressure to 60 MPa.

[0072] (6) After the sample extrusion is complete, 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 hot-extruded sample, cut and polish it for testing.

[0073] Example 2:

[0074] This embodiment prepares bismuth telluride-based thermoelectric materials via hot extrusion, with the chemical formula Bi. 0.48 Sb 1.52 Te3+3wt%Te+0.1 wt%Cu2Se;

[0075] 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 below 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use an acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0076] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750°C to melt, and keep it at this temperature for 30 minutes; then turn on the swing switch and swing at a rate of 30 times per minute for 30 minutes; after the swing is finished, turn off the swing switch; take out the quartz glass tube at 750°C while it is still hot, and place it vertically in a cooling tank to cool naturally.

[0077] (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.

[0078] (4) Remove the molten bismuth telluride alloy ingot from the completely cooled quartz tube and crush and grind it in a mortar for 30 minutes. Load 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 pre-form the hot extrusion blank after the vacuum degree is <10 Pa. Hold the blank at 60 MPa uniaxial pressure and 420°C for 5 minutes to obtain a cylindrical blank with a diameter of 16 mm.

[0079] (5) Place the precast blank in a position such as Figure 1 The diameter shown is 16 mm at the inlet and 10 mm at the outlet in a hot-extrusion graphite mold. The mold is then placed in a hot-press furnace, and a temperature probe is inserted. The vacuum pump is turned on, and after the vacuum level is <10 Pa, hot extrusion preparation of bismuth telluride is carried out. This process consists of two steps: 1) Preheating at 420℃ for 10 minutes without applying pressure to preheat the preform; 2) Gradually increasing the temperature to 460℃ while simultaneously applying pressure to 60 MPa.

[0080] (6) After the sample extrusion is complete, 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 hot-extruded sample, cut and polish it for testing.

[0081] Comparative Example 1:

[0082] This comparative example prepares bismuth telluride-based thermoelectric materials with the chemical formula Bi by zone melting. 0.48 Sb 1.52 Te3+3wt%Te;

[0083] Preparation method: (1) Weigh 7.50620 g of bismuth with a purity of 99.999%, 13.84910 g of antimony and 30.14475 g of tellurium 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 below 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use an acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0084] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750°C to melt, and keep it at this temperature for 30 minutes; then turn on the swing switch and swing at a rate of 30 times per minute for 30 minutes; after the swing is finished, turn off the swing switch; take out the quartz glass tube at 750°C while it is still hot, and place it vertically in a cooling tank to cool naturally.

[0085] (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.

[0086] (4) After removing the uneven parts at the head and tail of the sample prepared by zone melting, cut and polish it for testing.

[0087] Comparative Example 2:

[0088] This comparative example prepares bismuth telluride-based thermoelectric materials via hot pressing, with the chemical formula Bi. 0.48 Sb 1.52 Te3+3wt%Te;

[0089] Preparation method: (1) Weigh 7.50620 g of bismuth with a purity of 99.999%, 13.84910 g of antimony and 30.14475 g of tellurium 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 below 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use an acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0090] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750°C to melt, and keep it at this temperature for 30 minutes; then turn on the swing switch and swing at a rate of 30 times per minute for 30 minutes; after the swing is finished, turn off the swing switch; take out the quartz glass tube at 750°C while it is still hot, and place it vertically in a cooling tank to cool naturally.

[0091] (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.

[0092] (4) Remove the molten bismuth telluride alloy ingot from the completely cooled quartz tube and crush and grind it in a mortar for 30 minutes. Load the ground bismuth telluride particles into a 10 mm diameter hot-press graphite mold. Then place the mold in a hot-press furnace and insert a temperature probe into the mold. Turn on the vacuum pump and, once the vacuum level is <10 Pa, proceed with the hot-pressing preparation of bismuth telluride. The specific steps are as follows: gradually increase the temperature and pressure to 420℃ and 60 MPa.

[0093] (5) After holding the heat and pressure for 10 minutes, stop heating; after the mold cools down naturally, release the pressure, turn off the vacuum pump and take out the sample. Obtain the hot-pressed sample, cut and polish it for testing.

[0094] Comparative Example 3:

[0095] This comparative example prepared bismuth telluride samples with the chemical formula Bi using a hot-pressing texturing method. 0.48 Sb 1.52 Te3+3wt%Te;

[0096] Preparation method: (1) Weigh 7.50620 g of bismuth with a purity of 99.999%, 13.84910 g of antimony and 30.14475 g of tellurium 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 below 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use an acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0097] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750°C to melt, and keep it at this temperature for 30 minutes; then turn on the swing switch and swing at a rate of 30 times per minute for 30 minutes; after the swing is finished, turn off the swing switch; take out the quartz glass tube at 750°C while it is still hot, and place it vertically in a cooling tank to cool naturally.

[0098] (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.

[0099] (4) Remove the molten bismuth telluride alloy ingot from the completely cooled quartz tube and crush and grind it in a mortar for 30 minutes. Load the ground bismuth telluride particles into a metal mold (10 mm in diameter). Place the metal mold in a hydraulic press and press it into a cylindrical blank with a diameter of 10 mm under a uniaxial pressure of 20 MPa.

[0100] (5) Place the pre-made blank in a hot-press graphite mold with a diameter of 16 mm. Then place the mold in the hot-press furnace and insert a temperature probe into the mold. Turn on the vacuum pump and wait until the vacuum degree is <10 Pa before preparing the hot-press texture of bismuth telluride. Specifically, it is divided into two steps: 1) Preheat at 420℃ for 10 minutes without applying pressure to complete the preheating of the blank; 2) Gradually increase the temperature to 460℃ while gradually applying pressure to 60 MPa and hold the temperature and pressure for 10 minutes.

[0101] (6) After the hot-pressing texture of the sample is completed, stop heating and release the pressure. After the mold cools naturally, turn off the vacuum pump and remove the sample. Cut and polish the hot-pressed textured sample for testing.

[0102] Comparative Example 4:

[0103] This comparative example provides a bismuth telluride-based thermoelectric material and its preparation method, with the chemical formula Bi. 0.48 Sb 1.52 Te3+3wt%Te+0.1 wt%Cu2Se;

[0104] 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 below 10.0 Pa; turn on the molecular pump to further evacuate for 30 minutes to below 1.0 Pa; use an acetylene flame to heat the quartz glass tube rotating along the axis until the quartz glass tube is sealed.

[0105] (2) Place the sealed quartz glass tube containing the sample horizontally in a high-temperature swing furnace at 750°C to melt, and keep it at this temperature for 30 minutes; then turn on the swing switch and swing at a rate of 30 times per minute for 30 minutes; after the swing is finished, turn off the swing switch; take out the quartz glass tube at 750°C while it is still hot, and place it vertically in a cooling tank to cool naturally.

[0106] (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.

[0107] (4) Remove the molten 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) (without crushing or grinding). Then place the mold into a hot press furnace and insert a temperature probe into the mold. Turn on the vacuum pump and press the bismuth telluride after the vacuum degree is <10 Pa. Specifically, it is divided into two steps: 1) Preheat at 420℃ for 30 minutes without applying pressure to complete the preheating of the blank; 2) Gradually increase the temperature to 460℃, while gradually applying pressure to 60 MPa, and hold the temperature and pressure for 300 minutes.

[0108] (5) Place the pre-made blank in a hot extrusion graphite mold with an inlet diameter of 16 mm and an outlet diameter of 10 mm. The mold structure is as follows: Figure 1 As shown. Then, the mold is placed in the hot press furnace, and the temperature probe is inserted into the mold. The vacuum pump is turned on, and after the vacuum degree is <10 Pa, the hot extrusion preparation of bismuth telluride is carried out. Specifically, it is divided into two steps: 1) Preheating at 420℃ for 10 minutes without applying pressure to complete the preheating of the blank; 2) Gradually increasing the temperature to 460℃, while gradually applying pressure to 60MPa.

[0109] (6) After the sample extrusion is complete, 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 hot-extruded sample, cut and polish it for testing.

[0110] Experimental Example 1: This experimental example tested the structural features and performance of Examples 1-2 and Comparative Examples 1-4.

[0111] (1) Structural features:

[0112] like Figure 2 As shown, the X-ray diffraction (XRD) pattern reveals: Bi 0.48 Sb 1.52 The X-ray diffraction peaks of the Te3 sample and the standard X-ray diffraction pattern of the bismuth telluride-based sample revealed that the sample prepared in Example 1 was 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 conformed to the standard bismuth telluride spectrum, with no Cu2Se peaks. The difference was that the peak positions of the diffraction peaks in the Cu2Se-doped sample shifted to lower angles, which is due to the increase in the unit cell parameters caused by Cu2Se entering the bismuth telluride lattice.

[0113] like Figure 3 As shown, the scanning electron microscope morphology image and electron backscatter diffraction elemental distribution map show that: Bi prepared by hot extrusion method in Example 1 of this invention 0.48 Sb 1.52 The Te3 sample has a uniform elemental distribution and no second phase, which corresponds to the XRD results. Moreover, the polished surface of the sample is dense and free of pores.

[0114] (2) Performance testing:

[0115] The performance testing of the samples prepared in the embodiments and comparative examples of this invention is divided into two main parts: electrical performance and thermal performance. Electrical conductivity, Seebeck coefficient, and power factor are considered electrical performance parameters and were directly measured using a ZEM device manufactured by Riko (Japan). Specifically, a diamond wire cutter was used to cut the samples into 3*3*12 mm cuboids, which were then placed in the ZEM. Test temperatures were set at 30, 80, 130, 180, and 230°C to characterize the electrical performance. The samples were then cut into 10*10*1.5 mm squares using the same diamond wire cutter, and thermal conductivity was tested using a Laser Thermal Conductivity Analyzer (LFA) manufactured in Germany, with the same temperature settings as the electrical tests. Finally, μ was calculated based on the electrical and thermal performance parameters. W / κ l Value and zT value.

[0116] 1) Conductivity test:

[0117] like Figure 4 , Figure 9 As shown, the conductivity of the samples obtained in Examples 1-2 gradually decreased with increasing temperature, exhibiting metallic conductivity behavior. Among them, Bi... 0.48 Sb 1.52 The room temperature conductivity of the Te3 sample was 770 S cm. -1 The highest temperature conductivity is 351 S cm. -1 The conductivity of the Cu₂Se-doped sample was significantly improved across the entire temperature range, with room temperature conductivity and maximum temperature conductivity of 1553 S / cm and 590 S / cm, respectively. -1 .like Figure 14 As shown, the room temperature conductivity of the samples prepared in Comparative Examples 1-4 were 1137, 642, 866, and 1587 S / cm, respectively. -1 The highest temperature conductivity was 536, 371, 391 and 611 S cm, respectively. -1 .

[0118] 2) Seebeck coefficient test:

[0119] like Figure 5 , Figure 10As shown, Bi before and after Cu2Se doping 0.48 Sb 1.52 The Seebeck coefficients of the Te3 samples (samples obtained in Examples 1 and 2) varied with temperature, but were all positive, indicating they were P-type materials. The Bi sample obtained in Example 1... 0.48 Sb 1.52 The Seebeck value for the Te3 sample reached a maximum of 204 μVK near room temperature. -1 As temperature increases, its Seebeck coefficient gradually decreases to 180 μVK. -1 After Cu2Se doping, the Seebeck coefficient of the sample prepared in Example 2 decreased significantly, exhibiting a parabolic trend, that is, its Seebeck coefficient decreased from 155 μVK. -1 As the temperature gradually increases, it reaches a maximum value of 191 μVK near 445 K. -1 Then, as the temperature increases, it gradually decreases to 184 μVK. -1 .like Figure 15 As shown, the room temperature Seebeck coefficients of the samples prepared in Comparative Examples 1-4 were 204, 229, 215, and 170 μVK, respectively. -1 The highest SeeBeck coefficients were 222, 240, 237, and 202 μVK, respectively. -1 .

[0120] 3) Power factor test:

[0121] 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 decreased significantly after Cu2Se doping, the significantly increased conductivity still improved the sample's power factor. The power factor at room temperature after doping reached 37 μW / cm². -1 K -2 The highest temperature can reach 20 μW / cm². -1 K -2 The power factor was higher than that of the undoped sample prepared in Example 1 (32 μW / cm² at room temperature). -1 K -2 The highest temperature was 11 μW / cm². -1 K -2 ).like Figure 16 As shown, the room temperature power factors of the samples prepared in Comparative Examples 1-4 were 47, 34, 40, and 46 μW / cm², respectively. -1 K -2The power factors at the highest temperatures were 16, 11, 13, and 23 μW / cm², respectively. -1 K -2 .

[0122] 4) Thermal conductivity and lattice thermal conductivity tests:

[0123] like Figure 7 , Figure 12 As shown, the thermal conductivity of the sample was obtained using 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 For electronic thermal conductivity, L This is the Lorentz constant, calculated using the Seebeck coefficient of the sample. For example... Figure 7 As shown, Bi 0.48 Sb 1.52 The lowest thermal conductivity and lattice thermal conductivity of the Te3 sample were approximately 0.96 W / m² and 0.62 W / m², respectively. -1 K -1 After Cu₂Se doping, the lowest total thermal conductivity of the sample increased slightly to 0.97 W / m². -1 K -1 This is related to the increase in electronic thermal conductivity caused by the significant increase in electrical conductivity. Nevertheless, the lattice thermal conductivity of Cu₂Se doping is effectively reduced to 0.28 W / m². -1 K -1 This effectively reduces the lattice thermal conductivity of bismuth telluride. For example... Figure 17 , 18 As shown, the lowest thermal conductivity and lowest lattice thermal conductivity of the samples prepared in Comparative Examples 1-4 were 1.50, 1.14, 1.32, and 1.31 W / m, respectively. -1 K -1 And 1.00, 0.83, 0.95 and 0.63 Wm -1 K -1 .

[0124] 5) μ W / κ l test:

[0125] 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 3σ[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, m e K B Let μ and e be Planck's constant, pi, electron mass, Boltzmann constant, and electron charge, respectively. Calculate the μ of the sample. W / κ l value.

[0126] The μ of the bismuth telluride sample prepared by the hot extrusion process in Example 1 was calculated. W / κ l The value is 0.059 m 3 KV -1 s -1 W -1 This is superior to samples prepared by other strategies (comparative examples 1-3 μ). W / κ l The values ​​are 0.053, 0.049, and 0.051 m, respectively. 3 KV -1 s -1 W -1 Thanks to Cu2Se doping, the μ content of the sample in Example 2 was [missing information]. W / κ l The value increased to 0.15 m 3 KV -1 s -1 W -1 The sample prepared by the strategy in Comparative Example 4 was superior to that prepared by the strategy in Comparative Example 4 (μ of Comparative Example 4). W / κ l The value is 0.074 m 3 KV -1 s -1 W -1 ).

[0127] Table 1

[0128]

[0129] 6) Thermoelectric figure of merit test:

[0130] 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 was calculated. This is due to the μ-value after Cu₂Se doping. W / κ l The value has been greatly improved, and its thermoelectric optimal value has been significantly optimized, with the maximum zT Value 1.33. This represents a 27% improvement over the undoped sample's 1.05; and improvements of 36%, 49%, 38%, and 15% over the samples prepared in Comparative Examples 1-4, respectively (Comparative Examples 1-4...). zT The values ​​were 0.98, 0.89, 0.96 and 1.16 respectively.

[0131] 7) Room temperature P-type carrier concentration, effective carrier mass, and mobility testing:

[0132] As shown in Tables 2-3, the carrier concentrations of the samples prepared in Examples 1-2 of this invention are all positive, indicating they are P-type materials. Among them, the carrier concentration after Cu₂Se doping is 5.5 × 10⁻⁶. 19 cm -3 The concentration was significantly higher than that of the undoped carrier concentration (3.1 × 10⁻⁶). 19 cm -3 Based on carrier concentration and Seebeck coefficient, theoretical calculations revealed that the effective carrier mass of the Cu₂Se-doped sample is 0.93 m₀, which is lower than that of the undoped sample. This helps to improve the mobility of the material.

[0133] The test results further confirmed this, with the Cu₂Se-doped sample showing a mobility of 176.8 cm⁻¹. 2 V -1 s -1 It is higher than the undoped 156.8 cm⁻¹. 2 V -1 s -1 The increased carrier concentration and increased mobility together improved the conductivity of the sample.

[0134] Table 2

[0135]

[0136] Table 3

[0137]

[0138] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A bismuth telluride-based thermoelectric material, characterized by, The chemical composition of the thermoelectric material is: Bi 0.48 Sb 1.52 Te3+3wt%Te+ x wt% Cu2Se, where 0 < x < 0.1, and the material has at least one of the following properties: The room temperature carrier concentration is 3.1 x 1010cm"3 19 The room temperature carrier concentration is 5.5 x 1010cm"3 19 cm -3 ; The room temperature electrical conductivity is 770-1553 S / cm. Thermal conductivity is 0.96 ~ 0.97 Wm -1 K -1 ; μ W / κ l Values are 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; The Cu2Se enters the bismuth telluride lattice.

2. The bismuth telluride-based thermoelectric material of claim 1, wherein, When x=0.1 in the bismuth telluride-based thermoelectric material, the following performances are achieved: The room temperature carrier concentration is 5.5 x 1010cm-3 19 cm -3 -3. The room temperature electrical 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 / In the bismuth telluride-based thermoelectric material, the three elements of bismuth, antimony and tellurium are uniformly distributed, and the grain orientation is optimized through the hot extrusion process to form a densified microstructure. l value of 0.15 m 3 KV -1 s -1 W -1 .

3. The bismuth telluride-based thermoelectric material of claim 1, wherein, The Bi, Sb, Te and Cu2Se are weighed according to the stoichiometric ratio, mixed in a quartz glass tube, vacuum sealed, and sequentially subjected to melting swing, zone melting, crushing and pressing, hot extrusion molding and post-processing operations.

4. A method of producing a bismuth telluride-based thermoelectric material as claimed in any one of claims 1 to 3, characterized by, The sealing includes sequentially using a vacuum pump and a molecular pump for sealing operation, specifically, first opening the vacuum pump to pump for 10-20 minutes and ensuring that the air pressure in the tube is less than 10.0 Pa, then opening the molecular pump to further pump, 25-35 minutes to a pressure less than 1.0 Pa, then using acetylene flame or hydrogen-oxygen flame to heat the quartz glass tube rotating along the axial direction until the quartz glass tube is sealed.

5. The production method according to claim 4, wherein The melting swing specifically is: melting and keeping at 730-750℃ for 25-35 minutes, then swinging at 10-120 times / minute for 25-35 minutes; then moving the melting zone at a rate of 0.1-1.0 mm / minute at 715-725℃ to form a sharp bottom cylindrical alloy ingot with a diameter of 13-20 mm.

6. The production method according to claim 4, wherein The crushing and pressing specifically are: grinding the alloy ingot into 0.5-8 mm particles, placing the particles in a mold for hot pressing, preforming the hot extrusion blank under a vacuum degree of <10 Pa, and then pressing into a cylindrical blank with a diameter of 14-18 mm and a thickness of 18-20 mm at a uniaxial pressure of 45-65 MPa and a temperature of 400-430℃.

7. The production method according to claim 4, wherein The hot extrusion molding specifically is: preheating the blank to 400-420℃, then heating to 450-460℃ and applying a pressure of 55-65 MPa for extrusion; wherein the diameter of the mold entrance end is 14-18 mm, and the extrusion ratio during extrusion is 1.36-5.06; the extrusion process specifically is: first preheating at 400-430℃ for 8-10 minutes without applying pressure to complete the preheating of the blank; then gradually increasing the temperature to 450-480℃ while gradually applying a pressure of 55-65 MPa, and after the sample is extruded, stopping heating and removing the pressure; 8. The production method according to claim 4, wherein The post-processing includes removing the uneven parts at the head and tail of the sample, and cutting and polishing.

9. Application of the bismuth telluride-based thermoelectric material of any one of claims 1-3 in a thermoelectric refrigerator. ​

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