Sb-doped AgCuTe thermoelectric material and preparation method and application thereof

Abstract

The invention relates to a Sb-doped AgCuTe thermoelectric material and a preparation method and application thereof, the chemical formula of the thermoelectric material is AgCuSbxTe1-x, and x is 0.03-0.13. The preparation method comprises the following steps: mixing Ag powder, Cu powder, Te powder and Sb powder, grinding and drying; carrying out sintering treatment by using a discharge plasma sintering furnace; and sintering and cooling. The Sb-doped AgCuTe thermoelectric material prepared by the invention is suitable for being applied to a working environment in a medium and low temperature region of 300-573K. According to the AgCuTe thermoelectric material prepared by the method disclosed by the invention, the thermoelectric performance of the AgCuTe thermoelectric material is improved while the preparation energy and time are saved. Compared with other existing modified thermoelectric materials, the thermoelectric material AgCuSb0. 08Te0. 92 has the advantages that the thermoelectric figure of merit of the thermoelectric material AgCuSb0. 08Te0. 92 under the condition of 573K reaches 1.28, and is increased by about 64% compared with that of AgCuTe.

Description

Technical Field

[0001] The invention relates to the technical field of thermoelectric materials, in particular to a Sb-doped AgCuTe thermoelectric material and a preparation method and application thereof. Background Art

[0002] The ternary compound AgCuTe was found to have a more unique crystal structure and thermoelectric properties, belonging to the "phonon liquid-electron crystal" (PGEC) class of materials. In the medium and high temperature region, the ternary compound has a rock salt structure, and the highly mobile cations (Cu / Ag ions) help scatter heat-carrying phonons, while the rigid anions (chalcogen ions) provide a crystal path for carrier transport, which gives AgCuTe low thermal conductivity and medium electrical conductivity, enabling them to obtain lower thermal conductivity and higher thermoelectric performance than binary compounds.

[0003] In order to further improve the thermoelectric performance of AgCuTe thermoelectric materials at medium and low temperatures of 300-573K, the common doping elements currently used are Ni doping, Cu doping, S doping, etc. However, when using spark plasma sintering (SPS) to prepare thermoelectric materials, it is usually necessary to use pre-treatment methods such as sealed tube pre-sintering, mechanical ball milling alloying, or microwave heating of raw materials, which makes the process operation complicated and the equipment requires high cost and energy consumption. For example, ① sealed tube pre-sintering: It is usually necessary to heat to 723K and keep it warm for 12 hours, then heat to 1323K and keep it warm for 5 hours, and finally anneal for 12 hours, and cool to room temperature within 20 hours; ball milling is required after pre-sintering before spark plasma sintering can be performed. This method requires a lot of time for heating and insulation operations. ② Mechanical alloying pre-sintering: The raw material powders are mixed and partially alloyed by high-energy ball milling, and then pre-sintered for a short time at a lower temperature. However, impurities (such as grinding ball materials) may be introduced during the ball milling process, mechanical alloying may lead to uneven grain size distribution, and additional ball milling equipment is still required, which makes the process complicated. ③ Microwave pre-sintering: Use microwaves to heat the raw material powder for rapid pre-sintering. This method has a fast heating speed, is energy-efficient and efficient, can achieve selective heating, and promotes uniform reaction. However, it has requirements on the microwave absorption characteristics of the raw materials, and the equipment cost is relatively high.

[0004] Therefore, further research is needed on the doping elements and preparation methods of AgCuTe-based thermoelectric materials in order to simplify the preparation process, reduce energy consumption during the preparation process, and improve the thermoelectric performance of AgCuTe-based thermoelectric materials. Summary of the invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to further improve the thermoelectric performance of AgCuTe-based thermoelectric materials in the medium and low temperature range while simplifying the preparation process, and to reduce the energy consumption generated during the preparation process. To this end, the present invention provides a Sb-doped AgCuTe thermoelectric material and a preparation method and use thereof.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: A Sb-doped AgCuTe thermoelectric material, wherein the chemical formula of the thermoelectric material is AgCuSb x Te 1-x , where x is 0.03-0.13.

[0007] The above Sb-doped AgCuTe thermoelectric material has the chemical formula AgCuSb x Te 1-x , wherein x is 0.03, 0.05, 0.08, 0.1 or 0.13. Preferably, the chemical formula of the thermoelectric material is AgCuSb 0.08 Te 0.92 .

[0008] Among them, the present invention preferably uses Sb element to dope AgCuTe. On the one hand, from the perspective of material selection, Sb element is a low-priced metalloid element with the characteristics of being brittle and fusible, and is mainly used to manufacture alloys and semiconductor materials; Sb and Te belong to the same main group elements and have similar properties. Sb doping can partially replace Te and reduce dependence on the scarce element Te; Sb has low toxicity, and the environmental friendliness of the doped material is improved. On the one hand, from the perspective of performance, the introduction of Sb can change the band structure of the material, thereby improving the carrier mobility; the size and mass difference between Sb atoms and Te atoms is large, which will introduce strong point defect scattering in the lattice and significantly reduce the lattice thermal conductivity.

[0009] At the same time, the present invention adjusts the doping amount of Sb element. A certain amount of Sb doping can adjust the carrier concentration of AgCuTe. At the same time, a certain amount of Sb doping will introduce defects in the lattice, enhance phonon scattering, reduce lattice thermal conductivity, and improve its thermoelectric performance. However, excessive Sb doping will also cause defect recombination, resulting in reduced thermoelectric performance.

[0010] A method for preparing a Sb-doped AgCuTe thermoelectric material comprises the following steps: (1) According to the molar ratio of each element in the chemical formula of the thermoelectric material, Ag powder, Cu powder, Te powder and Sb powder are weighed and mixed to obtain a mixed powder A for later use; (2) adding anhydrous ethanol to the mixed powder A for grinding, and after the grinding is completed, a mixed powder B is obtained; (3) The mixed powder B is transferred into a graphite mold and placed in a spark plasma sintering furnace; (4) Sintering and cooling to obtain the above-mentioned Sb-doped AgCuTe thermoelectric material.

[0011] The thermoelectric performance of the Sb-doped AgCuTe thermoelectric material is improved at low temperatures of 300-573K. 0.08 Te 0.92 The thermoelectric figure of merit (ZT) is 1.28 at 573K, which is at the forefront of AgCuTe doping research data. On the other hand, from a process perspective, the present invention adopts a one-step spark plasma sintering method when preparing thermoelectric materials after Sb doping, without the need for a pre-sintering process, and avoids the disadvantages of ball milling and other methods of polluting sample powders, greatly saving sample preparation time and being energy-efficient and efficient.

[0012] The present invention prepares thermoelectric materials through a one-step SPS method without the need for pre-treatment such as preliminary sintering or ball milling. In other studies, it is usually necessary to adopt traditional sealed tube pre-sintering + SPS sintering, or mechanical ball milling alloying + sealed tube pre-sintering + SPS sintering, or use microwave heating of raw material powder for rapid pre-sintering. The core purpose of the pretreatment steps (such as mechanical alloying, pre-sintering, and microwave heating) is to provide SPS with raw material powder with uniform composition, fine particles, and stable structure, so as to ensure that the sintered material has a high density and avoid component segregation or phase separation. Therefore, other studies need to perform pre-treatment methods such as sealed tube pre-sintering, mechanical ball milling alloying, or microwave heating of raw materials before SPS sintering.

[0013] In contrast, the preparation method of the present invention is more energy-saving and simple under the premise of ensuring performance optimization. The present invention does not need to perform pre-treatment such as sealing tube pre-sintering, mechanical ball milling alloying or microwave heating of raw materials before SPS sintering. This is because the present invention uses Sb atoms as dopants, which can not only reduce the diffusion barrier of Ag, Cu, and Te atoms, accelerate element migration, but also the dynamic diffusion process makes each component quickly and evenly distributed during the sintering process, avoiding the performance degradation caused by component segregation in the traditional process. At the same time, the short-term sintering of SPS limits the growth of grains, and Sb doping forms a pinning effect at the grain boundary (such as Sb segregation at the grain boundary), further stabilizing the nanostructure and avoiding the problem of grain coarsening caused by traditional long-term pre-sintering. Therefore, the present invention synergizes Sb doping with the SPS one-step method, accelerates element diffusion, optimizes carrier concentration, regulates microstructure and dynamic reaction path, and only needs to control the grinding time and the amount of anhydrous ethanol used in the early manual grinding process to obtain uniform and fine powder, which can avoid the problem of component segregation or phase separation of the sintered material, and the obtained material has excellent medium and low temperature thermoelectric properties. In the method for preparing the Sb-doped AgCuTe thermoelectric material, in step (1), the purity of the Ag powder is 99.99wt%, and the particle size of the Ag powder is less than or equal to 1μm; the purity of the Cu powder is 99.99wt%, and the Cu powder passes through a 200-mesh sieve; the purity of the Te powder is 99.99wt%, and the Te powder passes through a 100-mesh sieve; and the purity of the Sb powder is 99.99wt%, and the Sb powder passes through a 100-mesh sieve.

[0014] The preparation method of the Sb-doped AgCuTe thermoelectric material, the specific method of step (2) is: putting the mixed powder A into a mortar, adding anhydrous ethanol that can fully wet the mixed powder A, and then manually grinding, the grinding time is 15-25min; the mass and volume ratio of the mixed powder A to the anhydrous ethanol is (5-5.5) g: 10 mL; under this grinding condition, at the end of grinding, the anhydrous ethanol can be completely evaporated to obtain a dry mixed powder B, without the need for pre-treatment such as sintering or ball milling.

[0015] In the method for preparing the Sb-doped AgCuTe thermoelectric material, in step (3), the diameter of the graphite mold is 15 mm.

[0016] In the method for preparing the Sb-doped AgCuTe thermoelectric material, in step (4), the sintering procedure is as follows: heating is started from room temperature, and pressurization is started at the same time as heating is started, and after reaching the target temperature and target pressure, the temperature and pressure are maintained; then, the mold pressure is released, and the sample is taken out of the mold after cooling to room temperature in the furnace.

[0017] In the preparation method of the Sb-doped AgCuTe thermoelectric material, in the step (4), the target heating temperature is 700-850°C (a sintering temperature that is too low will result in an incomplete reaction of the metal powder, and a sintering temperature that is too high will not only affect the microstructure of the thermoelectric material generated by the reaction and cause poor performance, but also cause the metal powder to overflow the mold due to melting during the sintering process), and the heating rate is 60-70°C / min (during the sintering process, heating too fast will increase the temperature gradient inside the sample, and thermal stress will be generated due to the large temperature difference between the surface and the core, which is easy to cause microcracks or even macro cracks; while heating too slow and staying at high temperature for a long time, especially for nanomaterials, will promote grain boundary migration, resulting in grain coarsening and poor performance; At the same time, too slow a heating rate will significantly prolong the sintering cycle, increase energy consumption, reduce production efficiency, and be uneconomical for industrial applications. Compared with the staged gradient heating, the present invention adopts a one-time uniform heating, which has the advantages that the material can directly reach a higher temperature range when heated, while maintaining good thermal stability, crack resistance and mechanical properties. The target pressure is 45-55MPa (during sintering, the mechanical stress on the mold increases significantly under excessively high pressure, especially for large-sized samples or long-term sintering, which can easily lead to mold cracking or permanent deformation, increasing equipment maintenance costs; but if the pressure is too low, it cannot effectively promote the plastic flow and rearrangement of the powder particles, resulting in uneven sintering and low efficiency), and the pressure increase rate is 3-5 MPa / min (during sintering, if the pressure is increased rapidly when the material is not fully preheated, the brittle particles may be broken due to stress concentration, which reduces the densification efficiency; and, when the pressure is increased rapidly, the mold is subjected to instantaneous high pressure, which can easily cause deformation, cracking or surface peeling of the graphite mold; if the pressure is applied too slowly, the material stays at high temperature for too long, and the grains may grow excessively and affect product performance); the heat preservation and pressure holding time is 3-5min (too short a holding time may lead to insufficient sintering, and too long a holding time may coarsen the grains and consume energy); the pressure reduction rate when the pressure is released is 0.8-1.2MPa / min. The present invention controls the heating rate, sintering temperature, pressure increase rate and sintering pressure during one-time uniform heating and sintering, and controls the heat preservation and pressure holding time and pressure reduction rate, so that the Sb-doped AgCuTe thermoelectric material obtained after sintering the mixed powder B has an ideal microstructure, so that Sb can give full play to its doping optimization effect on the thermoelectric properties of the AgCuTe thermoelectric material.

[0018] In the preparation method of the above-mentioned Sb-doped AgCuTe thermoelectric material, in the step (4), the sintering procedure is: heating from room temperature, the heating rate is 65°C / min, the target temperature is 800°C; the pressure increase rate is 4 MPa / min, the target pressure is 50 MPa; the heat and pressure holding time is 5 min; the pressure reduction rate when removing the mold pressure is 1 MPa / min.

[0019] A use of a Sb-doped AgCuTe thermoelectric material, wherein the Sb-doped AgCuTe thermoelectric material is used in a working environment in a medium-low temperature range of 300-573K.

[0020] The technical solution of the present invention achieves the following beneficial technical effects: The present invention relates to a Sb-doped AgCuTe thermoelectric material, and adopts a one-step SPS sintering method to prepare the thermoelectric material. While obtaining high thermoelectric performance, the preparation process is simplified, and the energy consumption generated in the preparation process is significantly reduced. The specific analysis is as follows: The present invention dopes Sb element at the Te position of AgCuTe thermoelectric material. Sb and Te belong to the same main group elements and have similar properties. Sb doping can partially replace Te and reduce the dependence on the scarce element Te. At the same time, Sb doping inhibits the formation of Cu2Te phase. The reduction of Cu2Te phase changes the performance balance of the mixed phase composition material and greatly improves its thermal performance. In addition, the introduction of Sb can change the band structure of the material, thereby improving the carrier mobility; since Sb doping can adjust the carrier concentration of AgCuTe, and the size and mass difference between Sb atoms and Te atoms is large, strong point defect scattering will be introduced into the lattice, significantly reducing the lattice thermal conductivity and improving the thermoelectric performance of the material; Sb doping will introduce defects into the lattice, enhance phonon scattering, and reduce the lattice thermal conductivity.

[0021] The present invention innovatively uses a one-step direct discharge plasma sintering method to prepare AgCuTe thermoelectric materials, saving preparation energy and time. Other processing steps before SPS sintering are eliminated. For example, the method of the present invention does not require tube sealing pre-sintering before SPS sintering, and does not need to spend a lot of time on heating and heat preservation operations in the tube sealing (usually about 50 hours). At the same time, Sb atoms, as dopants, can reduce the diffusion barriers of Ag, Cu, and Te atoms and accelerate element migration. This dynamic diffusion process allows each component to be quickly and evenly distributed during the sintering process, avoiding the performance degradation caused by component segregation in traditional processes. The short-term sintering of SPS limits grain growth, while Sb doping forms a pinning effect at the grain boundary (such as Sb segregation at the grain boundary), further stabilizing the nanostructure and avoiding grain coarsening caused by traditional long-term pre-sintering. The present invention utilizes the synergistic effect of Sb doping and the one-step SPS method to successfully replace the necessity of traditional tube sealing pre-sintering by accelerating element diffusion, optimizing carrier concentration, and regulating microstructure and dynamic reaction path. This technological innovation not only simplifies the preparation process, but also significantly improves the thermoelectric performance of AgCuTe through nanostructure design and energy band engineering, providing new ideas for the development of high-efficiency and low-cost thermoelectric materials.

[0022] Compared with other existing AgCuTe doped modified thermoelectric materials, the thermoelectric material AgCuSb prepared by the present invention is 0.08 Te0.92 The thermoelectric figure of merit reaches 1.28 at 573K, which is about 64% higher than that of AgCuTe. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1a A curve diagram showing the variation of the Seebeck coefficient of AgCuTe obtained in Example 2 of the present invention at different sintering temperatures as a function of temperature; Figure 1b A curve diagram showing the change of conductivity of AgCuTe obtained in Example 2 of the present invention at different sintering temperatures as a function of temperature; Figure 1c A curve diagram showing the power factor of AgCuTe obtained in Example 2 of the present invention changing with temperature at different sintering temperatures; Figure 2a A graph showing the variation of the Seebeck coefficient of AgCuTe obtained in Example 3 of the present invention with temperature at different holding times; Figure 2b A curve diagram showing the change of conductivity of AgCuTe obtained in Example 3 of the present invention with temperature at different holding times; Figure 2c A graph showing the power factor of AgCuTe obtained in Example 3 of the present invention changing with temperature at different holding times; Figure 3a A graph showing the variation of the Seebeck coefficient of AgCuTe obtained in Example 4 of the present invention with temperature at different pressures; Figure 3b A graph showing the change in conductivity of AgCuTe at different pressures as a function of temperature obtained in Example 4 of the present invention; Figure 3c A graph showing the power factor of AgCuTe obtained in Example 4 of the present invention changing with temperature at different pressures; Figure 4 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x XRD pattern with 2θ of 20-80°; Figure 5 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x The XRD pattern of 2θ is 64-68°; Figure 6 AgCuSb obtained in Example 1 of the present invention 0.08 Te 0.92 SEM-EDS morphology of Figure 7 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Seebeck coefficient curve diagram; Figure 8 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x The conductivity curve of Fig. 9 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Power factor curve diagram; Fig.10 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Total thermal conductivity curve of ; Fig.11 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x The lattice thermal conductivity curve of ; Fig.12 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x The electronic thermal conductivity curve of Fig.13 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Thermoelectric figure of merit curve. DETAILED DESCRIPTION

[0024] Example 1 This embodiment provides a method for preparing a Sb-doped AgCuTe thermoelectric material, comprising the following steps: (1) Weigh Ag powder, Cu powder, Te powder and Sb powder according to the molar ratio of each element in the chemical formula of the thermoelectric material and set aside; Among them, the purity of Ag powder is 99.99wt%, and the particle size of Ag powder is less than or equal to 1μm; the purity of Cu powder is 99.99wt%, and Cu powder passes through a 200-mesh sieve; the purity of Te powder is 99.99wt%, and Te powder passes through a 100-mesh sieve; the purity of Sb powder is 99.99wt%, and Sb powder passes through a 100-mesh sieve; Thermoelectric materials: AgCuTe, AgCuSb 0.03 Te 0.97 、AgCuSb 0.05 Te 0.95 、AgCuSb 0.08 Te 0.92 、AgCuSb 0.1 Te 0.9 、AgCuSb 0.13 Te 0.87 Sample preparation; For example, the masses of Ag powder, Cu powder, and Te powder corresponding to AgCuTe are 1.9416 g, 1.1438 g, and 2.2968 g; AgCuSb 0.03 Te 0.97 The corresponding masses of Ag powder, Cu powder, Sb powder, and Te powder are 1.9416 g, 1.1438 g, 0.0658 g, and 2.2279 g; AgCuSb 0.05 Te 0.95 The corresponding masses of Ag powder, Cu powder, Sb powder, and Te powder are 1.9416 g, 1.1438 g, 0.1096 g, and 2.1820 g; AgCuSb 0.08 Te 0.92 The corresponding masses of Ag powder, Cu powder, Sb powder, and Te powder are 1.9416 g, 1.1438 g, 0.1753 g, and 2.1131 g; AgCuSb 0.1 Te 0.9 The corresponding masses of Ag powder, Cu powder, Sb powder, and Te powder are 1.9416 g, 1.1438 g, 0.2192 g, and 2.0671 g; AgCuSb 0.13 Te 0.87 The corresponding masses of Ag powder, Cu powder, Sb powder, and Te powder are 1.9416 g, 1.1438 g, 0.2849 g, and 1.9982 g; (2) Put Ag powder, Cu powder, Te powder and Sb powder into a mortar and mix to obtain mixed powder A. Add 10 mL of anhydrous ethanol and grind thoroughly for 20 min until all the anhydrous ethanol evaporates to obtain dry mixed powder B. (3) The mixed powder B after the treatment in step (2) is transferred into a 15 mm diameter SPS-specific graphite mold and placed in a spark plasma sintering furnace; (4) The sintering procedure is as follows: heating from room temperature at a heating rate of 65°C / min to 800°C; pressurization is started at the same time as heating, at a pressure increase rate of 4 MPa / min, and the pressure reaches 50 MPa after 12.5 min; after reaching the target temperature and target pressure, the temperature and pressure are maintained for 5 min; (5) After the heat preservation and pressure maintenance, the pressure is released at a pressure reduction rate of 1 MPa / min. After the mold is cooled to room temperature in the furnace, the sample is taken out to obtain the above-mentioned thermoelectric materials. After the sample is polished, it is used for analysis and testing such as scanning and transmission.

[0025] Before exploring the preparation method of Sb-doped AgCuTe thermoelectric material, the present invention first takes the preparation of thermoelectric material AgCuTe as the basis, explores the influence of sintering temperature, sintering pressure and holding time in the sintering procedure on the thermoelectric properties of the obtained thermoelectric material AgCuTe, and then conducts Sb doping research under the optimal sintering process conditions.

[0026] Example 2 This embodiment provides a method for preparing a thermoelectric material AgCuTe. The thermoelectric material AgCuTe is prepared by referring to the method of Embodiment 1.

[0027] This example studies the effect of sintering temperature. The difference between this example and Example 1 is that the sintering procedure of step (4) is different, and the other steps and parameters are the same as those of Example 1.

[0028] The sintering procedure of step (4) of this embodiment is: heating from room temperature, with a heating rate of 65°C / min, heating to 400-850°C (respectively: 400°C, 500°C, 600°C, 700°C, 800°C, 850°C), and cooling with the furnace after reaching the target temperature.

[0029] Example 3 This embodiment provides a method for preparing a thermoelectric material AgCuTe. The thermoelectric material AgCuTe is prepared by referring to the method of Embodiment 1.

[0030] This example studies the effect of the holding time. The difference between this example and Example 1 is that the sintering procedure of step (4) is different, and the other steps and parameters are the same as those of Example 1.

[0031] The sintering procedure of step (4) of this embodiment is: heating from room temperature at a heating rate of 65°C / min to 800°C, and after reaching the target temperature, keeping the temperature for 0-5 min (respectively: 0 min, 3 min, 5 min).

[0032] Example 4 This embodiment provides a method for preparing a thermoelectric material AgCuTe. The thermoelectric material AgCuTe is prepared by referring to the method of Embodiment 1.

[0033] This example studies the effect of pressure. The difference between this example and Example 1 is that the sintering procedure of step (4) is different, and the other steps and parameters are the same as those of Example 1.

[0034] The sintering procedure of step (4) of this embodiment is as follows: heating is started from room temperature, with a heating rate of 65°C / min, and heating to 800°C; while heating, pressurization is started, with a pressure increase rate of 4MPa / min, and the pressure reaches 45-55MPa (respectively: 45MPa, 50MPa, and 55MPa); after reaching the target temperature and target pressure, the temperature and pressure are maintained for 5 minutes.

[0035] Comparative Example 1 This comparative example adopts the method in [Lanwei Li, Wenya Zhai, Chao Wang, et al. MaximizingphononscatteringefficiencybyCu2SealloyinginAgCuTethermoelectricmaterials[J].Journal ofMaterialsChemistryA,2022,10:6701–6712] to prepare a thermoelectric material AgCuTe-1%Cu2Se, comprising the following steps: (1) According to the stoichiometric ratio, weigh high-purity Ag powder with a purity of 99.99%, Cu powder with a purity of 99.99%, Te powder with a purity of 99.99%, and Cu2Se powder with a purity of 98%.

[0036] (2) Mix the powders evenly, place them in a cleaned quartz tube and seal it.

[0037] (3) Slowly heat to 723 K within 12 h, heat to 1323 K within 5 h, anneal for 12 h, and then slowly cool to room temperature within 20 h.

[0038] (4) The sample obtained by sealed tube sintering was ball milled at 250 rpm for 30 min.

[0039] (5) The ball-milled powder is sintered in a spark plasma sintering (SPS) system, starting with heating from room temperature, with a target sintering temperature of 823 K; while heating, pressurization is started, with a target pressure of 40 MPa.

[0040] Comparative Example 2 This comparative example adopts the method in [Jing Jiang, Hangtian Zhu, Yi Niu, et al. Achieving High Room-Temperature Thermoelectric Performance in CubicAgCuTe[J]. Journal of Materials Chemistry A, 2020, 8 (9): 4790-4799] to prepare a thermoelectric material (AgCu) 0.995 Te 0.9 Se 0.1 , including the following steps: (1) According to the stoichiometric method of the substances, the silver particles were weighed to have a purity of 99.99%, the copper particles were weighed to have a purity of 99.5%, the tellurium bulk was weighed to have a purity of 99.9% and the selenium particles were weighed to have a purity of 99.9%.

[0041] (2) All elements were loaded into a stainless steel can with stainless steel balls and then sealed in an argon atmosphere in a glove box and mechanically alloyed by a high-energy ball mill for 15 h.

[0042] (3) About 2 g of the obtained nanopowder was loaded into a graphite mold with an inner hole diameter of 12.7 mm and then hot-pressed at 473 K and heated at 77 MPa for 5 min with a heating rate of 100 K min -1 The hot pressed samples were cooled naturally in air.

[0043] Performance Testing: The thermoelectric materials obtained by the method of Example 1: AgCuTe, AgCuSb 0.03 Te 0.97 、AgCuSb 0.05 Te 0.95 、AgCuSb 0.08 Te 0.92 、AgCuSb 0.1 Te 0.9 、AgCuSb 0.13 Te 0.87 , the thermoelectric materials obtained in Examples 2-4 and Comparative Examples 1-2 were subjected to relevant performance tests: ① The Seebeck coefficient (S), conductivity (σ), and power factor (PF) of the thermoelectric materials obtained in Examples 2-4 were measured to analyze the sintering procedure of the thermoelectric material preparation method of the present invention. The test temperature range was 323-573K, and the temperature interval was 25K. The curves of Seebeck coefficient, conductivity, and power factor changing with temperature were obtained. The results are as follows: Figures 1a to 3c shown.

[0044] Figure 1a to Figure 1cThese are the thermoelectric performance diagrams of AgCuTe obtained in Example 2 at different sintering temperatures. It can be seen from the diagram that the power factor is optimal when the sintering temperature is 800°C. Figure 2a to Figure 2c They are the thermoelectric performance diagrams of AgCuTe obtained in Example 3 at different holding times. It can be seen from the figure that the power factor is optimal when the holding time is 5 min. Figure 3a to Figure 3c They are the thermoelectric performance diagrams of AgCuTe obtained in Example 4 at different pressures. It can be seen from the diagram that the power factor is optimal when the pressure is 50 MPa.

[0045] ② The samples were analyzed by X-ray diffractometer (Smartlab, Rigaku, Japan) in the 2θ range of 20°-80°. Figure 4 and Figure 5 shown.

[0046] in, Figure 4 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x of 2 θ XRD pattern of 20-80°; Figure 4 Display, AgCuSb x Te 1-x The diffraction peaks correspond to the PDF cards (PDF#03-065-4252, PDF#00-034-0142, PDF#00-057-0477), which confirms that all samples have hexagonal Ag at room temperature. 23.1 Cu 19.3 Te 24 phase, monoclinic Ag2Te phase and hexagonal Cu2Te phase.

[0047] Figure 5 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x The XRD pattern of 2θ is 40-43°; Figure 5 It is shown that due to the smaller ionic radius of Sb 3+ Replaced Te with a larger ionic radius 2- , the diffraction peaks of each sample shift slightly toward higher angles as the doping amount increases.

[0048] ③ Use field emission scanning electron microscopy (SEM, FEG-Quanta650) for morphological analysis and elemental analysis.

[0049] in, Figure 6 AgCuSb 0.08 Te 0.92 SEM-EDS morphology of Figure 6 Display, AgCuSb 0.08 Te0.92 The sample has three different phases, namely white Ag2Te area, gray Ag 23.1 Cu 19.3 Te 24 The dark grey Cu2Te region and the dark grey Cu2Te region, where the dark grey region accounts for a small proportion due to the fact that Sb doping inhibits the formation of the Cu2Te phase. Relatively speaking, Cu2Te has better performance in the high temperature range, and Ag2Te and AgCuTe have better performance in the medium and low temperature range. The present invention focuses on the medium and low temperature thermoelectric performance of the AgCuTe system, so it is beneficial to reduce the Cu2Te phase.

[0050] ④Electrical performance test: Use a Seebeck coefficient and resistivity tester (Lindesz, LSR-3) to measure the Seebeck coefficient and resistivity (later converted to conductivity). The reciprocal of the resistivity is the sample conductivity. The test temperature range is 323-573K, and the temperature interval is 25K. The Seebeck coefficient and conductivity curves changing with temperature are obtained.

[0051] in, Figure 7 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x Seebeck coefficient (S) curve; Figure 7 It shows that the Seebeck coefficients of Sb-doped samples are higher than those of pure phase samples.

[0052] Figure 8 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x Conductivity (σ) curve of Figure 8 It shows that the conductivity of the Sb-doped sample decreases.

[0053] ⑤ Thermal performance test: Fig. 9 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x Power factor (PF) curve, power factor is calculated by PF=S 2 The σ formula is used to calculate that the material power factor data can be directly derived using the LSR-3 Seebeck coefficient conductivity tester; Fig. 9 It shows that the maximum power factor of the Sb-doped sample is reduced, but the low-temperature power factor is improved. Under 323K, the power factor of the pure phase sample is almost 0, while the power factor of the doped sample is improved under low-temperature conditions. 0.08 Te 0.92 The power factor of the sample was increased to about 0.08 mWm -1 K -2This is attributed to the fact that the doped samples have a higher Seebeck coefficient than the pure phase samples under low temperature conditions. As the temperature increases, the cubic AgCuTe phase gradually becomes the main phase, and the power factor of the sample is also improved accordingly, while the conductivity of the sample also has the same trend. Under high temperature conditions, except for AgCuSb 0.08 Te 0.92 The power factor of the other doped samples is lower than that of the pure phase samples due to the coupling effect of slightly increased Seebeck coefficient and greatly decreased conductivity. 0.08 Te 0.92 The power factor of the sample is about 0.89 Wm at 573K -1 K -2 , which is similar to the pure phase sample. Through the above data analysis, Sb element doping has no obvious positive improvement on the electrical transport properties of AgCuTe materials.

[0054] The thermal diffusion coefficient was measured by a laser thermal conductivity meter (LFA-467). The measurement range of the sample was set to 323-573 K, and the heating step was 25 K. According to the specific heat capacity Cp (Dulong-Petit law), the thermal conductivity was further calculated.

[0055] in, Fig.10 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x Total thermal conductivity (K) curve; Fig.10 It shows that the thermal conductivity of the Sb-doped sample decreases, which is proportional to the decrease in electrical conductivity.

[0056] Fig.11 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x The lattice thermal conductivity (K l ) curve graph; Fig.11It shows that the lattice thermal conductivity of the Sb-doped sample decreases overall, but improves at high temperatures. The lattice thermal conductivity of the sample is calculated by subtracting the electronic thermal conductivity from the total thermal conductivity. The lattice thermal conductivity of most doped samples is lower than that of the pure phase sample. According to the XRD results, the doping element successfully replaces the Te sublattice, forming point defects, resulting in fluctuations in mass and strain. The difference in atomic radius between Sb and Te elements is large, which further increases the fluctuation. The larger the fluctuation, the stronger the phonon scattering ability, which greatly reduces the lattice thermal conductivity of the material. After 473K, the lattice thermal conductivity of the doped sample increases compared with the pure phase sample. This is due to the bipolar effect of the Ag2Te material. Cu2Te is a material with a complex crystal structure. It undergoes multiple phase transitions between room temperature 300 K and 850K. There are still many controversies about the phase transition process and temperature of the Cu2Te material. The reduction of the Cu2Te phase gives the doped sample a simpler crystal structure and improves the lattice thermal conductivity of the sample. At 573K, AgCuSb 0.08 Te 0.92 The sample lattice thermal conductivity is 0.19 Wm -1 K -1 , which is about 90% higher than that of pure phase samples. Through the analysis of the overall thermal properties of the samples, it is found that doping with Sb elements plays a certain role in reducing the thermal conductivity of AgCuTe samples and optimizing the thermoelectric properties of the materials.

[0057] Fig.12 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x Electronic thermal conductivity (Ke) curve of ; Fig.12 It shows that the electronic thermal conductivity of the Sb-doped sample decreases. The lower electronic thermal conductivity of the doped sample comes from the decrease in its electrical conductivity, which makes the contribution of electronic thermal conductivity to thermal conductivity lower than that of lattice thermal conductivity, and the trend of electronic thermal conductivity change is consistent with the trend of electrical conductivity change. The substantial decrease in electronic thermal conductivity may be related to the reduction of Cu2Te phase caused by Sb element doping. Cu2Te thermoelectric materials have a complex crystal structure, which has the characteristic of easy loss of Cu, which reduces the Seebeck coefficient of the material and increases the carrier thermal conductivity. And because the Cu2Te thermoelectric material shows P-type conductivity, the carrier (hole) concentration is too high, which to a certain extent increases the unbalanced electrical transport situation of the system with too high electrical conductivity and too low Seebeck coefficient. Therefore, the reduction of Cu2Te phase reduces the electronic thermal conductivity of the material. At 573K, AgCuSb 0.08 Te 0.92 The electronic thermal conductivity of the sample is about 0.21 Wm -1 K -1 , which is about 62% lower than that of pure phase samples.

[0058] ⑥Thermoelectric figure of merit: Fig.13AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x The dimensionless thermoelectric merit (ZT) curve of the material is given by ZT=S 2 σT / κ is calculated. The thermoelectric figure of merit ZT is directly related to the power factor PF, thermal conductivity κ and temperature T. Fig.13 It shows that doping with Sb element has little effect on the electrical properties of AgCuTe material, but greatly improves its thermal properties, and finally optimizes the thermoelectric figure of merit of the sample in the entire temperature range of 323-573K. 0.08 Te 0.92 At 573K, the thermoelectric figure of merit of the sample reached 1.28, an increase of about 64% compared with the pure phase.

[0059] Table 1 Sample data of Example 1 and Comparative Examples 1-2 at 573K Table 2 Sample data of Examples 2-4 at 573K According to the comparative analysis of Example 1 and Comparative Examples 1-2, the present invention innovatively uses a one-step direct spark plasma sintering method to prepare AgCuTe thermoelectric materials, saving preparation energy and time. Other processing steps before SPS sintering are omitted. For example, the method of the present invention does not require tube sealing pre-sintering before SPS sintering, and does not require a large amount of time for temperature rise and heat preservation operations in the tube sealing (usually about 50 hours).

[0060] The present invention selects Sb atoms as dopants. Sb and Te belong to the same main group elements and have similar properties. Sb doping can partially replace Te and reduce dependence on the scarce element Te. Sb doping can reduce the diffusion barrier of Ag, Cu, and Te atoms and accelerate element migration. This dynamic diffusion process allows each component to be quickly and evenly distributed during the sintering process, avoiding the performance degradation caused by component segregation in traditional processes. The short-term sintering of SPS limits grain growth, and Sb doping forms a pinning effect at the grain boundary (such as Sb segregation at the grain boundary), further stabilizing the nanostructure and avoiding grain coarsening caused by traditional long-term pre-sintering.

[0061] The present invention uses Sb doping to inhibit the formation of Cu2Te phase. Cu2Te is a P-type semiconductor material whose Seebeck coefficient is approximately 0 at room temperature, resulting in poor thermoelectric performance and a thermoelectric figure of merit that is also approximately 0. The reduction of the Cu2Te phase changes the performance balance of the mixed phase composition material, which has a small improvement in the electrical properties of the AgCuTe material, but greatly improves its thermal properties, and ultimately optimizes the thermoelectric figure of merit of the sample in the entire temperature range of 323-573K. As the amount of Sb element doping increases, the thermoelectric figure of merit of the sample is improved, but after the doping amount exceeds 0.08 mol%, this improvement shows a downward trend. Among them, AgCuSb 0.08 Te 0.92 The thermoelectric figure of merit of the sample is 1.28 at 573K, which is 64% higher than the thermoelectric figure of merit of 0.78 of the pure phase AgCuTe sample at this temperature, and is at the forefront of the research results of doping modification of AgCuTe thermoelectric materials. It can be seen that a certain amount of Sb element doping can adjust the carrier concentration of AgCuTe. At the same time, a certain amount of Sb doping will introduce defects in the lattice, enhance phonon scattering, and reduce the lattice thermal conductivity. Excessive doping may cause the recombination of defects and reduce its thermoelectric performance.

[0062] The present invention utilizes the synergistic effect of SPS one-step method and Sb doping to successfully replace the necessity of traditional tube sealing and pre-sintering by accelerating element diffusion, optimizing carrier concentration, and regulating microstructure and dynamic reaction path. This process innovation not only simplifies the preparation process, but also significantly improves the thermoelectric performance of AgCuTe through nanostructure design and energy band engineering, providing a new idea for the development of high-efficiency and low-cost thermoelectric materials.

[0063] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A Sb-doped AgCuTe thermoelectric material, characterized in that: The chemical formula of the thermoelectric material is AgCuSb x Te 1-x , where x is 0.03-0.

13.

2. The Sb-doped AgCuTe thermoelectric material according to claim 1, characterized in that: The chemical formula of the thermoelectric material is AgCuSb 0.08 Te 0.92 .

3. A method for preparing a Sb-doped AgCuTe thermoelectric material, characterized in that: The following steps are involved: (1) According to the molar ratio of each element in the chemical formula of the thermoelectric material according to claim 1 or 2, Ag powder, Cu powder, Te powder and Sb powder are weighed and mixed to obtain a mixed powder A for use; (2) adding anhydrous ethanol to the mixed powder A for grinding, and after the grinding is completed, a mixed powder B is obtained; (3) Transferring the mixed powder B into a graphite mold and placing it in a spark plasma sintering furnace; (4) Sintering and cooling to obtain the Sb-doped AgCuTe thermoelectric material as claimed in claim 1 or 2.

4. The method for preparing the Sb-doped AgCuTe thermoelectric material according to claim 3, characterized in that: In the step (1), the purity of the Ag powder is 99.99wt%, and the particle size of the Ag powder is less than or equal to 1μm; the purity of the Cu powder is 99.99wt%, and the Cu powder passes through a 200-mesh sieve; The purity of Te powder is 99.99wt%, and the Te powder passes through a 100-mesh sieve; the purity of Sb powder is 99.99wt%, and the Sb powder passes through a 100-mesh sieve.

5. The method for preparing the Sb-doped AgCuTe thermoelectric material according to claim 3, characterized in that: In the step (2), the grinding method is: manual grinding in a mortar for 15-25 minutes; the mass of the mixed powder and the volume ratio of the mixed powder to anhydrous ethanol are (5-5.5) g: 10 mL.

6. The method for preparing the Sb-doped AgCuTe thermoelectric material according to claim 3, characterized in that: In the step (3), the diameter of the graphite mold is 15 mm.

7. The method for preparing the Sb-doped AgCuTe thermoelectric material according to claim 3, characterized in that: In the step (4), the sintering procedure is: heating from room temperature, and starting pressurization at the same time as heating, and after reaching the target temperature and target pressure, heat preservation and pressure maintenance are performed; then the mold pressure is released, and the mold is removed from the mold after cooling to room temperature in the furnace.

8. The method for preparing the Sb-doped AgCuTe thermoelectric material according to claim 7, characterized in that: In the step (4), the target temperature for heating is 700-850°C, and the heating rate is 60-70°C / min; the target pressure is 45-55MPa, and the pressure increasing rate is 3-5MPa / min; the time for heat preservation and pressure holding is 3-5min; and the pressure reduction rate when the pressure is released is 0.8-1.2MPa / min.

9. The method for preparing the Sb-doped AgCuTe thermoelectric material according to claim 8, characterized in that: In the step (4), the sintering procedure is as follows: heating from room temperature, the heating rate is 65°C / min, the target temperature is 800°C; the pressure increase rate is 4 MPa / min, the target pressure is 50 MPa; the heat and pressure holding time is 5 min; the pressure reduction rate when removing the mold pressure is 1 MPa / min.

10. Use of a Sb-doped AgCuTe thermoelectric material, characterized in that: The Sb-doped AgCuTe thermoelectric material as claimed in claim 1 or 2 is used in a medium-low temperature working environment of 300-573K.

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