Powder metallurgy method for improving carrier concentration stability of polycrystalline bismuth telluride material

Abstract

The invention relates to the field of semiconductor material preparation, and discloses a powder metallurgy method for improving the carrier concentration stability of a polycrystalline bismuth telluride material, air contact is isolated under the technological process of the powder metallurgy method, so that the donor-like effect is effectively eliminated, the carrier concentration of the polycrystalline bismuth telluride material is kept stable, and the stability of the carrier concentration of the polycrystalline bismuth telluride material is improved. Therefore, the performance stability and repeatability are improved, and the problems that the polycrystalline bismuth telluride material prepared through a powder metallurgy method is poor in stability and difficult to repeat are solved.

Description

Technical Field

[0001] The invention relates to the field of semiconductor material preparation, and in particular to a powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride materials. Background Art

[0002] Bismuth telluride is the only semiconductor thermoelectric material that has been commercialized. Thermoelectric coolers based on bismuth telluride are irreplaceable in medical temperature control, vehicle refrigeration, civil refrigeration, optical communication temperature control, etc. The mainstream technology for preparing bismuth telluride is zone melting technology, which can obtain highly oriented bismuth telluride crystal rods. However, zone melting crystal rods have poor mechanical properties and are easily cleaved and broken during processing and service. The yield rate is not high, and it is impossible to prepare micro thermoelectric coolers.

[0003] In order to meet the strength requirements of the core material of the micro thermoelectric cooler, powder metallurgy was introduced to prepare polycrystalline bismuth telluride materials, such as patent CN113161473B, which uses fine grain strengthening to improve material strength. However, a large amount of experimental data shows that the carrier concentration of polycrystalline bismuth telluride materials prepared by powder metallurgy is very unstable, resulting in unstable thermoelectric properties and poor repeatability of polycrystalline bismuth telluride materials prepared by powder metallurgy, which seriously restricts the application of powder metallurgy in production.

[0004] When polycrystalline bismuth telluride materials are prepared by powder metallurgy, the donor-like effect will be generated during the powder making and sintering process, so the carrier concentration of the polycrystalline bismuth telluride material is very unstable, and the conductivity type may even change from P-type to N-type, resulting in unqualified material performance and ultimately low yield rate of thermoelectric coolers. Summary of the invention

[0005] In order to solve the technical problem mentioned in the background technology that the carrier concentration is unstable when polycrystalline bismuth telluride materials are prepared by powder metallurgy, resulting in unqualified material performance, the present invention provides a powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride materials. Under the original powder metallurgy process flow, air contact is isolated, the donor-like effect is eliminated, the carrier concentration of the polycrystalline bismuth telluride material is stabilized, and the yield rate of the thermoelectric cooler is improved.

[0006] The specific technical solution of the present invention is: a powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride material, comprising the following steps: a) Take the Te block and perform vacuum high temperature purification, wherein the temperature is 265-540°C and the vacuum degree is less than 10 -3 Pa; b) vacuum sealing the Bi block and the Te block purified in step a) and then smelting at high temperature to obtain a bismuth telluride smelting ingot, the vacuum degree is less than 10 -3Pa; c) crushing the bismuth telluride smelting ingot obtained in step b) to obtain bismuth telluride powder, wherein the crushing process is carried out under an inert gas; d) placing the bismuth telluride powder obtained in step c) into a mold for sintering under elevated temperature and pressure to obtain a polycrystalline bismuth telluride block, wherein the sintering process is performed in a vacuum state with a vacuum degree of <10 -3 Pa.

[0007] A large amount of research data shows that the carrier concentration of polycrystalline bismuth telluride materials prepared by powder metallurgy is unstable. After a lot of research, the team of the present invention found that the unstable carrier concentration is due to the donor-like effect that causes the increase of the electron concentration of the polycrystalline bismuth telluride material, which ultimately leads to the unstable thermoelectric properties of the polycrystalline bismuth telluride material prepared by powder metallurgy and poor repeatability. Therefore, the team of the present invention isolates the entire powder metallurgy process (including smelting, crushing and powder making, loading molds and high-temperature sintering) from contact with air, thereby eliminating the donor-like effect, stabilizing the carrier concentration of the polycrystalline bismuth telluride material, enhancing the stability and repeatability of the thermoelectric properties of the polycrystalline bismuth telluride material, and increasing the yield rate of the thermoelectric refrigerator prepared.

[0008] Specifically, Bi and Te blocks are weighed according to stoichiometry.

[0009] Furthermore, in step b), the temperature of high temperature smelting is 800-1000°C.

[0010] Furthermore, in step b), the high temperature smelting time is 3 to 12 hours.

[0011] Preferably, in step b), air cooling is performed after smelting is completed.

[0012] Furthermore, in step c), the crushing time is 30 to 40 seconds.

[0013] Furthermore, in step c), the median value of the powder particle size is 15 to 25 μm.

[0014] Furthermore, in step c), the inert gas is one of argon and nitrogen.

[0015] Preferably, the bismuth telluride powder obtained in step c) is placed in the mold under the protection of an inert gas throughout the entire process.

[0016] Furthermore, in step d), after the temperature-raising and pressure-treating sintering, the mixture is isolated from air before cooling to room temperature.

[0017] Preferably, in step d), the mold is a metal mold.

[0018] Furthermore, in step d), the heating temperature is 400-500°C.

[0019] Furthermore, in step d), the pressurization pressure is 50 to 80 MPa.

[0020] Furthermore, in step d), the sintering time is 30 to 60 minutes.

[0021] Compared with the prior art, the beneficial effects of the present invention are: the powder metallurgy method is isolated from air throughout the entire process, effectively eliminating the donor-like effect when preparing polycrystalline bismuth telluride materials, achieving the stability of carrier concentration, enhancing the repeatability of carrier concentration, and improving the yield rate of the manufactured thermoelectric cooler. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a graph showing the electrical properties of the polycrystalline bismuth telluride material in Example 1.

[0023] Figure 2 This is a graph showing the electrical properties of the polycrystalline bismuth telluride material in Comparative Example 2. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the embodiments.

[0025] Among them, the negative value of the Seebeck coefficient indicates that the main carriers in the bismuth telluride material prepared by this method are electrons, and the absolute value of the Seebeck coefficient is small. At the same time, the conductivity is high, indicating that the electron concentration is very high.

[0026] Example 1 A powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride material comprises the following steps: 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0027] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0028] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0029] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0030] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0031] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0032] Specifically, the crushing time is 30s.

[0033] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0034] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0035] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0036] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystal obtained in step 4) are tested, and the obtained data are shown in the figure below. Figure 1 shown.

[0037] Comparative Example 1 The difference between this comparative example and Example 1 is that in step (2), the quartz tube to be smelted is not vacuum sealed (i.e., air contact is set during the smelting process), and the rest of the process is the same as that of Example 1. The specific steps are as follows: 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0038] 2) Melting According to the stoichiometric weight, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0039] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0040] Specifically, the crushing time is 30s.

[0041] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0042] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0043] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0044] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0045] Comparative Example 2 The difference between this comparative example and Example 1 is that, in step 23), air contact is provided during the crushing and milling process, and the rest of the process is the same as that of Example 1, and the specific steps are as follows: 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0046] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0047] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0048] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0049] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0050] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in air to obtain bismuth telluride powder.

[0051] Specifically, the crushing time is 30s.

[0052] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0053] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in air, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0054] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0055] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystal obtained in step 4) are tested, and the obtained data are shown in the figure below. Figure 2 shown.

[0056] Comparative Example 3 The difference between this comparative example and Example 1 is that in step 4), the sintering process is not vacuumed (i.e., the sintering process is in contact with air), and the rest of the process is the same as Example 1, and the specific steps are as follows: 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0057] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0058] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0059] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0060] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0061] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0062] Specifically, the crushing time is 30s.

[0063] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0064] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, and sintered at 500° C. and 80 MPa for 30 minutes to obtain a polycrystalline bismuth telluride material.

[0065] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride material obtained in step 4) are tested.

[0066] Table 1 Effect of air contact on the Seebeck coefficient of the final formed polycrystalline bismuth telluride crystals Table 2 Effect of air contact on the conductivity of the final formed polycrystalline bismuth telluride crystals From the data in Tables 1 and 2, we can conclude that in each step of the powder metallurgy process (smelting, crushing and powder making, high-temperature sintering), any step contacting with air will directly affect the Seebeck coefficient of the final bismuth telluride material to be negative, and as the temperature increases, the absolute value increases, and the conductivity decreases with increasing temperature. The reason is speculated to be that when there is air contact in any process of the powder metallurgy process, it will lead to the occurrence of a donor-like effect in the bismuth telluride material obtained by the final sintering, and the electron concentration will increase significantly, which will reduce the stability and repeatability of the carrier concentration.

[0067] Example 2 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 280°C and the vacuum degree was 0.6*10-3Pa.

[0068] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 950° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0069] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0070] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0071] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0072] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0073] Specifically, the crushing time is 30s.

[0074] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0075] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0076] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0077] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0078] Example 3 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0079] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0080] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0081] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0082] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0083] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of argon gas to obtain bismuth telluride powder.

[0084] Specifically, the crushing time is 30s.

[0085] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0086] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0087] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0088] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0089] Example 4 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0090] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0091] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0092] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0093] Specifically, the vacuum degree is 10 -3 Pa.

[0094] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0095] Specifically, the crushing time is 35s.

[0096] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 20 μm.

[0097] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0098] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0099] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0100] Example 5 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0101] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0102] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0103] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0104] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0105] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0106] Specifically, the crushing time is 40s.

[0107] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0108] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0109] Specifically, the vacuum degree is 0.8*10 -3 Pa.

[0110] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0111] Example 6 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0112] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0113] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0114] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0115] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0116] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0117] Specifically, the crushing time is 30s.

[0118] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0119] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 450° C. and 60 MPa for 50 min to obtain polycrystalline bismuth telluride crystals.

[0120] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0121] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0122] Example 7 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 280°C and the vacuum degree was 0.6*10-3Pa.

[0123] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0124] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0125] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0126] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0127] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0128] Specifically, the crushing time is 30s.

[0129] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 25 μm.

[0130] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 480° C. and 80 MPa for 40 minutes to obtain polycrystalline bismuth telluride crystals.

[0131] Specifically, the vacuum degree is 0.8*10 -3 Pa.

[0132] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0133] Example 8 1) Raw material purification Take the Te block and perform vacuum high temperature purification, where the temperature is 350℃ and the vacuum degree is 0.6*10 -3 Pa.

[0134] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 980° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0135] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0136] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0137] Specifically, the vacuum degree is 10 -3 Pa.

[0138] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0139] Specifically, the crushing time is 40s.

[0140] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0141] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 80 MPa for 30 minutes to obtain polycrystalline bismuth telluride crystals.

[0142] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0143] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0144] Example 9 1) Raw material purification The Te block was taken for vacuum high-temperature purification, wherein the temperature was 350°C and the vacuum degree was 0.6*10-3Pa.

[0145] 2) Melting According to the chemical measurement, the Bi block and the Te block obtained in step 1) are weighed and placed in a clean quartz tube, the quartz tube is vacuum-sealed, and the sealed quartz tube is smelted at 1000° C. in a tube furnace for 5 hours. After the smelting is completed, the bismuth telluride smelting ingot is prepared.

[0146] Specifically, the tube sealing method is hydrogen-oxygen flame sealing.

[0147] Specifically, the vacuum is achieved by combining a mechanical pump with a molecular pump.

[0148] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0149] 3) Crushing and milling The bismuth telluride smelting ingot obtained in step 2) is crushed in a glove box under the protection of nitrogen to obtain bismuth telluride powder.

[0150] Specifically, the crushing time is 30s.

[0151] Specifically, the median value of the particle size of the obtained bismuth telluride powder was 15 μm.

[0152] 4) High temperature sintering The bismuth telluride powder obtained in step (3) is placed in a metal mold in a nitrogen-protected glove box, transferred to a sintering furnace, evacuated, and sintered at 500° C. and 50 MPa for 60 minutes to obtain polycrystalline bismuth telluride crystals.

[0153] Specifically, the vacuum degree is 0.6*10 -3 Pa.

[0154] 5) Performance testing The electrical properties of the polycrystalline bismuth telluride crystals obtained in step 4) are tested.

[0155] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0156] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride material, characterized in that: The following steps are involved: a) Take the Te block and perform vacuum high temperature purification, where the temperature is 265~540℃ and the vacuum degree is less than 10 -3 Pa; b) vacuum sealing the Bi block and the Te block purified in step a) and then smelting at high temperature to obtain a bismuth telluride smelting ingot, the vacuum degree is less than 10 -3 Pa; c) crushing the bismuth telluride smelting ingot obtained in step b) to obtain bismuth telluride powder, wherein the crushing process is carried out under an inert gas; d) placing the bismuth telluride powder obtained in step c) into a mold for heating and pressurizing sintering to obtain a polycrystalline bismuth telluride block, wherein the sintering process is in a vacuum state with a vacuum degree of <10 -3 Pa.

2. A powder metallurgy method for improving carrier concentration stability of polycrystalline bismuth telluride material according to claim 1, characterized in that: In step b), the high temperature smelting temperature is 800-1000°C.

3. A powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride material according to claim 1 or 2, characterized in that: In step b), the high temperature smelting time is 3 to 12 hours.

4. The powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride material according to claim 1, characterized in that: In step c), the crushing time is 30 to 40 seconds.

5. The powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride material according to claim 1, characterized in that: In step c), the median value of the powder particle size is 15-25 μm.

6. A powder metallurgy method for improving carrier concentration stability of polycrystalline bismuth telluride material according to claim 1, 4 or 5, characterized in that: In step c), the inert gas is argon or nitrogen.

7. The powder metallurgy method for improving the carrier concentration stability of polycrystalline bismuth telluride material according to claim 1, characterized in that: In step d), after the temperature-raising and pressure-treating sintering, the mixture is isolated from the air before cooling to room temperature.

8. A powder metallurgy method for improving carrier concentration stability of polycrystalline bismuth telluride material according to claim 1 or 7, characterized in that: In step d), the heating temperature is 400-500°C.

9. A powder metallurgy method for improving carrier concentration stability of polycrystalline bismuth telluride material according to claim 1 or 7, characterized in that: In step d), the pressurization pressure is 50-80 MPa.

10. A powder metallurgy method for improving carrier concentration stability of polycrystalline bismuth telluride material according to claim 1 or 7, characterized in that: In step d), the sintering time is 30 to 60 minutes.

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