A thermoelectric material of Sb-doped AgCuTe, its preparation method and uses

Abstract

The present invention relates to a thermoelectric material of Sb-doped AgCuTe, a preparation method thereof, and uses thereof. The chemical formula of the thermoelectric material is AgCuSb x Te 1‑x , where x is 0.03 - 0.13. The preparation method includes: mixing, grinding, and drying Ag powder, Cu powder, Te powder, and Sb powder; performing sintering treatment using a spark plasma sintering furnace; and obtaining the product after sintering and cooling. The thermoelectric material of Sb-doped AgCuTe prepared by the present invention is suitable for application in a working environment in the medium and low temperature range of 300 - 573K. The AgCuTe thermoelectric material prepared by the present invention improves the thermoelectric performance of the AgCuTe thermoelectric material while saving preparation energy and time. Compared with other existing modified thermoelectric materials, the thermoelectric figure of merit of the thermoelectric material AgCuSb 0.08 Te 0.92 reaches 1.28 at 573K, which is about 64% higher than that of AgCuTe.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and specifically to a thermoelectric material of Sb-doped AgCuTe, its preparation method and uses. Background Art

[0002] The ternary compound AgCuTe has been found to have a more unique crystal structure and thermoelectric properties, belonging to the "phonon liquid - electron crystal" (PGEC) type of materials. In the medium and high temperature regions, the ternary compound has a rock salt structure. The highly mobile cations (Cu / Ag ions) contribute to scattering the heat-carrying phonons, while the rigid anions (chalcogenide ions) provide a crystallization path for carrier transport, enabling AgCuTe to have a low thermal conductivity and a medium electrical conductivity, so that they can obtain a lower thermal conductivity and higher thermoelectric properties than binary compounds.

[0003] To further improve the thermoelectric properties of AgCuTe thermoelectric materials at medium and low temperatures of 300 - 573K, common doping elements currently include Ni doping, Cu doping, S doping, etc. However, when preparing thermoelectric materials using spark plasma sintering (SPS), pretreatment methods such as sealed tube pre-sintering, mechanical ball milling alloying, or microwave heating of raw materials are usually required, making the process operation complex, and the equipment requirements, cost, and energy consumption relatively high. For example, ① Sealed tube pre-sintering: Usually, it is necessary to first heat to 723K and hold for 12h, then heat to 1323K and hold for 5h, finally anneal for 12h, and cool to room temperature within 20h; after pre-sintering, ball milling treatment is still required before spark plasma sintering can be carried out. This method requires a large amount of time for heating and holding operations. ② Mechanical alloying pre-sintering: The raw material powders are mixed and partially alloyed by high-energy ball milling, and then pre-sintered at a lower temperature for a short time. However, impurities (such as ball milling material) 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, making the process complex. ③ Microwave pre-sintering: The raw material powders are heated by microwave to perform rapid pre-sintering. This method has a fast heating rate, is energy-saving and efficient, can achieve selective heating, and promotes uniform reaction. However, it has requirements for the microwave absorption characteristics of the raw materials, and the equipment cost is relatively high.

[0004] Therefore, it is still necessary to further study the doping elements and their preparation methods of AgCuTe-based thermoelectric materials to simplify the preparation process, reduce the energy consumption during the preparation process, and improve the thermoelectric properties of AgCuTe-based thermoelectric materials at the same time. Summary of the Invention

[0005] Aiming at the deficiencies 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 regions while simplifying the preparation process, and reduce the energy consumption generated during the preparation process. To this end, the present invention provides a thermoelectric material of Sb-doped AgCuTe, its preparation method and use.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A thermoelectric material of Sb-doped AgCuTe, the chemical formula of the thermoelectric material is AgCuSb x Te 1-x , where x is 0.03 - 0.13.

[0008] The above thermoelectric material of Sb-doped AgCuTe has the chemical formula AgCuSb x Te 1-x , where 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 .

[0009] 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-cost metalloid element with the characteristics of being brittle and fusible, and it 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 the dependence on the scarce element Te; Sb has low toxicity, and the environmental friendliness of the material is improved after doping. On the other hand, from the perspective of performance, the introduction of Sb can change the energy band structure of the material, thereby improving the carrier mobility; the size and mass difference between Sb atoms and Te atoms are relatively large, which will introduce strong point defect scattering in the lattice and significantly reduce the lattice thermal conductivity.

[0010] At the same time, the present invention regulates the doping amount of Sb element. 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, reduce the lattice thermal conductivity, and improve its thermoelectric performance. However, excessive doping of Sb will also cause the recombination of defects, resulting in a decrease in its thermoelectric performance.

[0011] A preparation method of a thermoelectric material of Sb-doped AgCuTe, comprising the following steps:

[0012] (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, mix them, and obtain a mixed powder A for standby;

[0013] (2)Add anhydrous ethanol to the mixed powder A and grind it. After grinding, obtain the mixed powder B;

[0014] (3)Transfer the mixed powder B into a graphite mold and place it in a spark plasma sintering furnace;

[0015] (4)Sinter and cool to obtain the above-mentioned Sb-doped AgCuTe thermoelectric material.

[0016] In the thermoelectric material of Sb-doped AgCuTe of the present invention, the thermoelectric performance is improved at low and medium temperatures of 300 - 573K. Among them, AgCuSb 0.08 Te 0.92 has a thermoelectric figure of merit (ZT) of 1.28 at 573K, ranking among the top of the research data on AgCuTe doping. On the other hand, from a process perspective, after adopting Sb doping in the present invention, a one-step spark plasma sintering method is used in the preparation of the thermoelectric material, without the need for a pre-sintering process, and it also avoids the drawbacks of contamination of the sample powder by ball milling, etc., greatly saving the preparation time of the sample and being energy-saving and efficient.

[0017] The present invention prepares the thermoelectric material by a one-step SPS method without the need for pre-treatment such as pre-sintering or ball milling. In other studies, it is usually necessary to use a traditional sealed-tube method for pre-sintering + SPS sintering, or mechanical ball milling alloying + sealed-tube method for pre-sintering + SPS sintering, or use microwave heating of the raw material powder for rapid pre-sintering. The core purpose of the pre-treatment steps (such as mechanical alloying, pre-sintering, microwave heating) is to provide raw material powder with uniform composition, fine particles and stable structure for SPS, so as to ensure that the sintered material has high density and avoid composition segregation or phase separation. Therefore, other studies need to carry out pre-treatment methods such as sealed-tube pre-sintering, mechanical ball milling alloying or microwave heating of the raw material before SPS sintering.

[0018] In contrast, the preparation method of the present invention is more energy-efficient and simple while ensuring performance optimization. Before SPS sintering, the present invention does not require pre-sintering in a sealed tube, mechanical ball milling alloying, or microwave heating of raw materials, etc. This is because the present invention selects Sb atoms as dopants, which can not only reduce the diffusion barriers of Ag, Cu, and Te atoms and accelerate element migration, but also enable the components to be rapidly and uniformly distributed during the sintering process through this dynamic diffusion process, avoiding the performance degradation caused by composition segregation in traditional processes. At the same time, the short-time sintering of SPS limits grain growth, and Sb doping forms a pinning effect at the grain boundaries (such as Sb segregation at the grain boundaries), further stabilizing the nanostructure and avoiding the problem of grain coarsening caused by traditional long-time pre-sintering. Therefore, the present invention combines Sb doping and SPS one-step method synergistically. By accelerating element diffusion, optimizing carrier concentration, regulating microstructure, and dynamic reaction path, it is only necessary to control the grinding time and the amount of absolute ethanol in the early manual grinding process to obtain uniform and fine powders, thus avoiding composition segregation or phase separation problems in the sintered material, and the obtained material has excellent thermoelectric properties at medium and low temperatures.

[0019] For the preparation method of the above-mentioned Sb-doped AgCuTe thermoelectric material, in step (1), the purity of the Ag powder is 99.99 wt%, and the particle size of the Ag powder is less than or equal to 1 μm; the purity of the Cu powder is 99.99 wt%, and the Cu powder passes through a 200-mesh sieve; the purity of the Te powder is 99.99 wt%, and the Te powder passes through a 100-mesh sieve; the purity of the Sb powder is 99.99 wt%, and the Sb powder passes through a 100-mesh sieve.

[0020] For the preparation method of the above-mentioned Sb-doped AgCuTe thermoelectric material, the specific method of step (2) is: put the mixed powder A into a mortar, add absolute ethanol that can fully moisten the mixed powder A and then manually grind it for 15 - 25 min; the mass ratio of the mixed powder A to the volume of absolute ethanol is (5 - 5.5) g:10 mL; under this grinding condition, at the end of grinding, the absolute ethanol can be completely volatilized to obtain a dry mixed powder B, without the need for pre-treatment such as pre-sintering or ball milling.

[0021] For the preparation method of the above-mentioned Sb-doped AgCuTe thermoelectric material, in step (3), the diameter of the graphite mold is 15 mm.

[0022] For the preparation method of the above-mentioned Sb-doped AgCuTe thermoelectric material, in step (4), the sintering procedure is: start heating from room temperature, start pressurizing while starting heating, after reaching the target temperature and target pressure, carry out heat preservation and pressure holding; then relieve the pressure of the mold, and cool it in the furnace to room temperature and then take out the sample from the mold.

[0023] For the preparation method of the above-mentioned Sb-doped AgCuTe thermoelectric material, in step (4), the target heating temperature is 700 - 850 °C (if the sintering temperature is too low, the reaction of metal powders will be insufficient; if the sintering temperature is too high, it will not only affect the microstructure of the thermoelectric material formed by the reaction, resulting in poor performance, but also the metal powders will overflow the mold due to melting during sintering), the heating rate is 60 - 70 °C / min (during sintering, if the heating rate is too fast, the internal temperature gradient of the sample will increase, and thermal stress will be generated due to the large temperature difference between the surface and the core, easily causing microcracks or even macroscopic cracking; if the heating rate is too slow and there is a long-time high-temperature stay, especially for nanomaterials, it will promote grain boundary migration, resulting in grain coarsening and poor performance; at the same time, an overly slow heating rate will significantly extend the sintering cycle, increase energy consumption, and reduce production efficiency, which is uneconomical for industrial applications); compared with staged gradient heating, the present invention adopts one-time uniform heating, and its advantages are that the material can directly reach a relatively high temperature range when heated, while maintaining good thermal stability, with better crack resistance and mechanical properties; the target pressure is 45 - 55 MPa (during sintering, the mechanical stress borne by the mold under too high pressure increases significantly, especially in the case of large-sized samples or long-time sintering, which easily leads to mold cracking or permanent deformation, increasing the equipment maintenance cost; if the pressure is too low, however, it cannot effectively promote the plastic flow and rearrangement of powder particles, resulting in uneven sintering and low efficiency), the pressure increase rate is 3 - 5 MPa / min (during sintering, if the pressure is increased rapidly when the material is not fully preheated, brittle particles may break due to stress concentration, instead reducing the densification efficiency; moreover, when the pressure is increased rapidly, the mold bears an instantaneous high pressure, easily causing deformation, cracking or surface spalling of the graphite mold; if the pressure is applied too slowly, the material stays at a high temperature for too long, and the grains may grow excessively, affecting the product performance); the time for heat preservation and pressure holding is 3 - 5 min (if the pressure holding time is too short, sintering may be insufficient; if the pressure holding time is too long, the grains will coarsen and energy will be consumed); the pressure reduction rate when relieving the pressure is 0.8 - 1.2 MPa / min. By controlling the heating rate, sintering temperature, pressure increase rate and sintering pressure during one-time uniform heating sintering, and controlling the heat preservation and pressure holding time and pressure reduction rate, the present invention can enable the Sb-doped AgCuTe thermoelectric material obtained after sintering of the mixed powder B to have an ideal microstructure, enabling Sb to fully exert its doping and optimization effect on the thermoelectric performance of the AgCuTe thermoelectric material.

[0024] For the preparation method of the above-mentioned Sb-doped AgCuTe thermoelectric material, in step (4), the sintering procedure is: starting from room temperature, heating at a heating rate of 65 °C / min, with a target temperature of 800 °C; the pressure increase rate is 4 MPa / min, and the target pressure is 50 MPa; the time for heat preservation and pressure holding is 5 min; the pressure reduction rate when relieving the mold pressure is 1 MPa / min.

[0025] Use of a thermoelectric material of Sb-doped AgCuTe, applying the above-mentioned thermoelectric material of Sb-doped AgCuTe in a working environment in the medium and low temperature range of 300 - 573K.

[0026] The technical solution of the present invention has achieved the following beneficial technical effects:

[0027] The present invention relates to a thermoelectric material of Sb-doped AgCuTe, and adopts a one-step SPS sintering method for the preparation of the thermoelectric material. While obtaining high thermoelectric performance, the preparation process is simplified, and the energy consumption generated during the preparation process is significantly reduced. The specific analysis is as follows:

[0028] In the present invention, Sb element is doped at the Te site of the AgCuTe thermoelectric material. Sb and Te belong to the same main group elements and have similar properties. Sb doping can partially replace Te, reducing the dependence on the scarce element Te. At the same time, Sb doping inhibits the formation of the Cu2Te phase. The reduction of the Cu2Te phase changes the performance balance of the mixed-phase composition material, significantly improving its thermal performance. In addition, the introduction of Sb can change the energy band structure of the material, thereby increasing 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 are 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, enhancing phonon scattering and reducing the lattice thermal conductivity.

[0029] The present invention innovatively uses a one-step direct discharge plasma sintering method to prepare the AgCuTe thermoelectric material, saving preparation energy and time. It omits other pretreatment steps before SPS sintering. For example, the method of the present invention does not require pre-sintering of the sealed tube before SPS sintering, and there is no need to spend a large amount of time on the heating and heat preservation operations in the sealed tube (usually about 50h). At the same time, as a dopant, Sb atoms can reduce the diffusion barrier of Ag, Cu, and Te atoms, accelerating the element migration. This dynamic diffusion process enables the components to be quickly and evenly distributed during the sintering process, avoiding the performance degradation caused by composition segregation in the traditional process. The short-time sintering of SPS limits the grain growth, and Sb doping forms a pinning effect at the grain boundaries (such as Sb segregation at the grain boundaries), further stabilizing the nanostructure and avoiding the grain coarsening caused by traditional long-time pre-sintering. The present invention utilizes the synergistic effect of Sb doping and the SPS one-step method, and successfully replaces the necessity of traditional sealed tube pre-sintering by accelerating element diffusion, optimizing carrier concentration, 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.

[0030] Compared with other existing doped and modified AgCuTe thermoelectric materials, the thermoelectric material AgCuSb prepared by the present invention 0.08 Te 0.92 has a thermoelectric figure of merit reaching 1.28 at 573K, which is about 64% higher than that of AgCuTe. Description of the Drawings

[0031] Figure 1a The graph showing the variation of the Seebeck coefficient with temperature of AgCuTe obtained in Example 2 of the present invention at different sintering temperatures;

[0032] Figure 1b The graph showing the variation of the electrical conductivity with temperature of AgCuTe obtained in Example 2 of the present invention at different sintering temperatures;

[0033] Figure 1c The graph showing the variation of the power factor with temperature of AgCuTe obtained in Example 2 of the present invention at different sintering temperatures;

[0034] Figure 2a The graph showing the variation of the Seebeck coefficient with temperature of AgCuTe obtained in Example 3 of the present invention at different holding times;

[0035] Figure 2b The graph showing the variation of the electrical conductivity with temperature of AgCuTe obtained in Example 3 of the present invention at different holding times;

[0036] Figure 2c The graph showing the variation of the power factor with temperature of AgCuTe obtained in Example 3 of the present invention at different holding times;

[0037] Figure 3a The graph showing the variation of the Seebeck coefficient with temperature of AgCuTe obtained in Example 4 of the present invention at different pressures;

[0038] Figure 3b The graph showing the variation of the electrical conductivity with temperature of AgCuTe obtained in Example 4 of the present invention at different pressures;

[0039] Figure 3c The graph showing the variation of the power factor with temperature of AgCuTe obtained in Example 4 of the present invention at different pressures;

[0040] Figure 4 XRD patterns of AgCuTe and AgCuSb x Te 1-x obtained in Example 1 of the present invention with 2θ ranging from 20° to 80°;

[0041] Figure 5 AgCuTe and AgCuSb x Te 1-xXRD pattern with 2θ ranging from 64° to 68°;

[0042] Figure 6 AgCuSb obtained in Example 1 of the present invention 0.08 Te 0.92 SEM-EDS morphology diagram;

[0043] Figure 7 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Seebeck coefficient curve graph;

[0044] Figure 8 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Conductivity curve graph;

[0045] Figure 9 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Power factor curve graph;

[0046] Figure 10 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Total thermal conductivity curve graph;

[0047] Figure 11 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Lattice thermal conductivity curve graph;

[0048] Figure 12 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Electronic thermal conductivity curve graph;

[0049] Figure 13 AgCuTe and AgCuSb obtained in Example 1 of the present invention x Te 1-x Thermoelectric figure of merit curve graph. Detailed implementation manners

[0050] Example 1

[0051] This example provides a preparation method of a thermoelectric material of Sb-doped AgCuTe, comprising the following steps:

[0052] (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;

[0053] Among them, the purity of Ag powder is 99.99 wt%, and the particle size of Ag powder is less than or equal to 1 μm; the purity of Cu powder is 99.99 wt%, and the Cu powder passes through a 200-mesh sieve; the purity of Te powder is 99.99 wt%, and the Te powder passes through a 100-mesh sieve; the purity of Sb powder is 99.99 wt%, and the Sb powder passes through a 100-mesh sieve.

[0054] Thermoelectric materials: AgCuTe and AgCuSb are prepared in an amount of 0.018 mol respectively. 0.03 Te 0.97 and AgCuSb 0.05 Te 0.95 and AgCuSb 0.08 Te 0.92 and AgCuSb 0.1 Te 0.9 and AgCuSb 0.13 Te 0.87 Sample preparation;

[0055] 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 respectively.

[0056] AgCuSb 0.03 Te 0.97 The masses of Ag powder, Cu powder, Sb powder, and Te powder corresponding to it are 1.9416 g, 1.1438 g, 0.0658 g, and 2.2279 g respectively.

[0057] AgCuSb 0.05 Te 0.95 The masses of Ag powder, Cu powder, Sb powder, and Te powder corresponding to it are 1.9416 g, 1.1438 g, 0.1096 g, and 2.1820 g respectively.

[0058] AgCuSb 0.08 Te 0.92 The masses of Ag powder, Cu powder, Sb powder, and Te powder corresponding to it are 1.9416 g, 1.1438 g, 0.1753 g, and 2.1131 g respectively.

[0059] AgCuSb 0.1 Te 0.9 The masses of Ag powder, Cu powder, Sb powder, and Te powder corresponding to it are 1.9416 g, 1.1438 g, 0.2192 g, and 2.0671 g respectively.

[0060] AgCuSb 0.13 Te 0.87 The masses of Ag powder, Cu powder, Sb powder, and Te powder corresponding to it are 1.9416 g, 1.1438 g, 0.2849 g, and 1.9982 g respectively.

[0061] (2) Put Ag powder, Cu powder, Te powder and Sb powder into a mortar, mix to obtain mixed powder A, add 10 mL of absolute ethanol and grind thoroughly for 20 min. At this time, all the absolute ethanol volatilizes, and dry mixed powder B is obtained.

[0062] (3) Transfer the mixed powder B processed in step (2) into a special SPS graphite mold with a diameter of 15 mm and place it in a spark plasma sintering furnace.

[0063] (4) The sintering procedure is as follows: Start heating from room temperature, with a heating rate of 65 °C / min, and heat to 800 °C. Start pressurizing simultaneously while starting to heat, with a pressure increasing rate of 4 MPa / min. After 12.5 min, the pressure reaches 50 MPa. After reaching the target temperature and target pressure, keep the temperature and pressure constant for 5 min.

[0064] (5) After the temperature and pressure are kept constant, relieve the pressure at a pressure decreasing rate of 1 MPa / min. After the mold cools down to room temperature with the furnace, take out the sample, and the above-mentioned thermoelectric materials are obtained. After polishing the sample, it is used for analysis and testing such as scanning and transmission.

[0065] Before exploring the preparation method of the Sb-doped AgCuTe thermoelectric material in the present invention, first, based on the preparation of the thermoelectric material AgCuTe, explore the influence of sintering temperature, sintering pressure, and holding time in the sintering procedure on the thermoelectric performance of the obtained thermoelectric material AgCuTe, and then conduct research on Sb doping under the optimal sintering process conditions.

[0066] Example 2

[0067] This example provides a preparation method of a thermoelectric material AgCuTe, and the preparation of the thermoelectric material AgCuTe is carried out with reference to the method of Example 1.

[0068] This example studies the influence of sintering temperature. The difference between this example and Example 1 is that the sintering procedure in step (4) is different, and other steps and parameters are the same as those in Example 1.

[0069] The sintering procedure in step (4) of this example is as follows: Start heating from room temperature, with a heating rate of 65 °C / min, and heat to 400 - 850 °C (respectively: 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, 850 °C). After reaching the target temperature, cool down with the furnace.

[0070] Example 3

[0071] This example provides a preparation method of a thermoelectric material AgCuTe, and the preparation of the thermoelectric material AgCuTe is carried out with reference to the method of Example 1.

[0072] This example studies the influence of the holding time. The difference between this example and Example 1 lies in that the sintering procedure in step (4) is different, and the other steps and parameters are the same as those in Example 1.

[0073] The sintering procedure in step (4) of this example is as follows: heating starts from room temperature at a heating rate of 65 °C / min until 800 °C is reached. After reaching the target temperature, hold for 0 - 5 min (respectively: 0 min, 3 min, 5 min).

[0074] Example 4

[0075] This example provides a method for preparing a thermoelectric material AgCuTe, and the method for preparing the thermoelectric material AgCuTe is carried out with reference to the method of Example 1.

[0076] This example studies the influence of the pressure. The difference between this example and Example 1 lies in that the sintering procedure in step (4) is different, and the other steps and parameters are the same as those in Example 1.

[0077] The sintering procedure in step (4) of this example is as follows: heating starts from room temperature at a heating rate of 65 °C / min until 800 °C is reached; while heating, start pressurizing at a pressure increasing rate of 4 MPa / min until the pressure reaches 45 - 55 MPa (respectively: 45 MPa, 50 MPa, 55 MPa); after reaching the target temperature and target pressure, hold the pressure for 5 min.

[0078] Comparative Example 1

[0079] This comparative example uses the method in [Lanwei Li, Wenya Zhai, Chao Wang, et al. Maximizing phonon scattering efficiency by Cu2Se alloying in AgCuTe thermoelectric materials[J]. Journal of Materials Chemistry A, 2022, 10: 6701–6712] to prepare a thermoelectric material AgCuTe-1%Cu2Se, including the following steps:

[0080] (1) 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% according to the stoichiometric ratio.

[0081] (2) Mix these powders evenly and seal them in a cleaned quartz tube.

[0082] (3) Heat it slowly to 723 K within 12 h, raise the temperature to 1323 K within 5 h, anneal for 12 h, and then cool it slowly to room temperature within 20 h.

[0083] (4) The sample obtained by sealed-tube sintering is ball-milled using a ball mill for 30 minutes at a rotation speed of 250 rpm.

[0084] (5) The milled powder is sintered in a spark plasma sintering system (SPS). Heat starts from room temperature, and the target sintering temperature is 823 K; pressure starts to be applied while heating, and the target pressure is 40 MPa.

[0085] Comparative Example 2

[0086] This comparative example prepares a thermoelectric material (AgCu) 0.995 Te 0.9 Se 0.1 using the method in [Jing Jiang, Hangtian Zhu, Yi Niu, et al. Achieving HighRoom-Temperature Thermoelectric Performance in CubicAgCuTe[J]. Journal ofMaterials Chemistry A, 2020, 8 (9): 4790-4799], including the following steps:

[0087] (1) Weigh silver particles with a purity of 99.99%, copper particles with a purity of 99.5%, tellurium bulk with a purity of 99.9% and selenium particles with a purity of 99.9% according to the stoichiometry of the substances.

[0088] (2) Load all the elements into a stainless-steel can with stainless-steel balls, then seal it in an argon atmosphere inside a glove box, and mechanically alloy it for 15 h using a high-energy ball mill.

[0089] (3) Load about 2 g of the obtained nano-powder into a graphite mold with an inner hole diameter of 12.7 mm, then hot-press it at 473 K, heat it at 77 MPa for 5 min, and the heating rate is 100 K min -1 . The hot-pressed sample is naturally cooled in air.

[0090] Performance Test:

[0091] For 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 Te0.92 , AgCuSb 0.1 Te 0.9 , AgCuSb 0.13 Te 0.87 , Perform relevant performance tests on the thermoelectric materials obtained in Examples 2-4 and Comparative Examples 1-2:

[0092] ① Measure the Seebeck coefficient (S), electrical conductivity (σ), and power factor (PF) of the thermoelectric materials obtained in Examples 2-4, and analyze the sintering process of the preparation method of the thermoelectric materials of the present invention. The test temperature range is 323 - 573 K, and the temperature interval is 25 K. Obtain the curve graphs of the Seebeck coefficient, electrical conductivity, and power factor changing with temperature. The results are as Figures 1a to 3c shown.

[0093] Figures 1a to 1c are the thermoelectric performance graphs of AgCuTe obtained in Example 2 at different sintering temperatures. It can be seen from the figure that the power factor is the best at a sintering temperature of 800 °C. Figures 2a to 2c are the thermoelectric performance graphs of AgCuTe obtained in Example 3 at different holding times. It can be seen from the figure that the power factor is the best when holding for 5 min. Figures 3a to 3c are the thermoelectric performance graphs of AgCuTe obtained in Example 4 at different pressures. It can be seen from the figure that the power factor is the best at a pressure of 50 MPa.

[0094] ② Analyze the samples within the 2θ range of 20° - 80° by an X-ray diffractometer (Smartlab, Rigaku, Japan). The results are as Figure 4 and Figure 5 shown.

[0095] Among them, Figure 4 is the XRD pattern of AgCuTe and AgCuSb x Te 1-x at 2 θ is the XRD pattern from 20° to 80°; Figure 4 shows that the diffraction peaks of AgCuSb x Te 1-x correspond to the PDF cards (PDF#03-065-4252, PDF#00-034-0142, PDF#00-057-0477). It can be determined that all samples have a hexagonal Ag 23.1 Cu 19.3 Te 24 phase, a monoclinic Ag2Te phase, and a hexagonal Cu2Te phase at room temperature.

[0096] Figure 5 is the XRD pattern of AgCuTe and AgCuSb x Te 1-xXRD pattern with 2θ of 40 - 43°; Figure 5 It shows that due to Sb with a smaller ionic radius 3+ replacing Te with a larger ionic radius 2- , with the increase of the doping amount, the diffraction peaks of each sample show a slight shift towards the high - angle direction.

[0097] ③Morphological and elemental analyses were carried out using a field - emission scanning electron microscope (SEM, FEG - Quanta650).

[0098] Among them, Figure 6 is the SEM - EDS morphology map of AgCuSb 0.08 Te 0.92 ; Figure 6 It shows that the AgCuSb 0.08 Te 0.92 sample has three different phases, namely the white Ag2Te region, the gray Ag 23.1 Cu 19.3 Te 24 region and the dark - gray Cu2Te region. Among them, due to the suppression of the formation of the Cu2Te phase by Sb doping, the proportion of the dark - gray region is relatively small. Relatively speaking, the Cu2Te phase has better performance in the high - temperature range, while Ag2Te and AgCuTe have better performance in the middle - and low - temperature ranges. The present invention focuses on the middle - and low - temperature thermoelectric performance of the AgCuTe system. Therefore, the reduction of the Cu2Te phase is beneficial.

[0099] ④Electrical property test: The Seebeck coefficient and resistivity were measured using a Seebeck coefficient and resistivity tester (Lindesz, LSR - 3). (The resistivity was later converted to conductivity). The reciprocal of the resistivity is the conductivity of the sample. The test temperature range was 323 - 573K, and the temperature interval was 25K. The curves of the Seebeck coefficient and conductivity varying with temperature were obtained.

[0100] Among them, Figure 7 is the curve of the Seebeck coefficient (S) of AgCuTe and AgCuSb x Te 1-x obtained by the method of Example 1; Figure 7 It shows that the Seebeck coefficients of the samples doped with Sb are all higher than those of the pure - phase samples.

[0101] Figure 8 is the curve of the conductivity (σ) of AgCuTe and AgCuSb x Te 1-x obtained by the method of Example 1; Figure 8 It shows that the conductivity of the samples doped with Sb decreases.

[0102] ⑤Thermal property test:

[0103] Figure 9AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x Power factor (PF) curve graphs, where the power factor is calculated by the formula PF = S 2 σ. The power factor data of the material can be directly derived using an LSR-3 type Seebeck coefficient conductivity tester; Figure 9 shows that the highest value of the power factor of the doped Sb sample decreases, but the power factor at low temperatures is improved. At 323 K, the power factor of the pure-phase sample is almost 0, while the power factor of the doped samples is improved under low-temperature conditions. For the AgCuSb 0.08 Te 0.92 sample, the power factor is increased to approximately 0.08 mWm -1 K -2 . This is attributed to the fact that under low-temperature conditions, the doped samples have a higher Seebeck coefficient than the pure-phase samples. As the temperature increases, the cubic AgCuTe phase gradually becomes the main phase, and the power factor of the sample also increases accordingly, and the conductivity of the sample shows the same trend of change. Under high-temperature conditions, except for the AgCuSb 0.08 Te 0.92 sample, for the other doped samples, due to the coupling effect of a slightly increased Seebeck coefficient and a significantly decreased conductivity, their power factors are lower than those of the pure-phase samples. The power factor of the AgCuSb 0.08 Te 0.92 sample is approximately 0.89 Wm -1 K -2 at 573 K, similar to the pure-phase sample. Through the above data analysis, the doping of Sb element has no obvious positive improvement on the electrical transport properties of the AgCuTe material.

[0104] The thermal diffusivity is measured by a laser thermal conductivity meter (LFA-467). The measurement range of the sample is set to 323 - 573 K, and the heating step is 25 K. According to the specific heat capacity Cp (Dulong-Petit law), the thermal conductivity is further calculated.

[0105] Among them, Figure 10 is the total thermal conductivity (K) curve graph of AgCuTe and AgCuSb x Te 1-x obtained by the method of Example 1; Figure 10 shows that the thermal conductivity of the doped Sb sample decreases, which is proportional to the decrease in conductivity.

[0106] Figure 11 is the lattice thermal conductivity (K x Te 1-x graph of AgCuTe and AgCuSb l obtained by the method of Example 1; Figure 11The results show that the lattice thermal conductivity of the Sb-doped samples generally decreases, but it increases at high temperatures. The lattice thermal conductivity of the samples 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 samples. According to the XRD results, the doped elements successfully replace the Te sublattice, forming point defects, which lead to fluctuations in mass and strain. Moreover, the atomic radius difference between Sb and Te elements is relatively large, further enhancing the fluctuations. The greater the fluctuations, the stronger the phonon scattering ability, resulting in a significant reduction in the lattice thermal conductivity of the material. After 473 K, the lattice thermal conductivity of the doped samples shows an increase compared with that of the pure-phase samples. This is due to the bipolar effect of the Ag2Te material. Cu2Te is a material with a complex crystal structure and undergoes multiple phase transitions between room temperature (300 K) and 850 K. There are still many controversies in the research on the phase transition process and temperature of the Cu2Te material. The reduction of the Cu2Te phase makes the doped samples have a simpler crystal structure, improving the lattice thermal conductivity of the samples. At 573 K, AgCuSb 0.08 Te 0.92 The lattice thermal conductivity of the sample is 0.19 Wm -1 K -1 , which is about 90% higher than that of the pure-phase sample. Through the analysis of the overall thermal properties of the samples, doping with Sb elements plays a certain role in reducing the thermal conductivity of the AgCuTe samples and optimizing the thermoelectric properties of the materials.

[0107] Figure 12 is the curve graph of the electronic thermal conductivity (Ke) of AgCuTe and AgCuSb x Te 1-x obtained by the method of Example 1; Figure 12 The results show that the electronic thermal conductivity of the Sb-doped samples decreases. The lower electronic thermal conductivity of the doped samples is due to the reduction of their electrical conductivity, making the contribution of the electronic thermal conductivity to the thermal conductivity lower than that of the lattice thermal conductivity. The change trend of the electronic thermal conductivity is consistent with that of the electrical conductivity. The significant reduction in the electronic thermal conductivity may be related to the reduction of the Cu2Te phase caused by the doping of Sb elements. The Cu2Te thermoelectric material has a complex crystal structure and the characteristic of easy Cu deficiency, which leads to a decrease in the Seebeck coefficient and an increase in the carrier thermal conductivity of the material. Moreover, because the Cu2Te thermoelectric material shows P-type conductivity, the carrier (hole) concentration is too high, which to a certain extent exacerbates the unbalanced electrical transport situation of too high electrical conductivity and too low Seebeck coefficient in this system. Therefore, the reduction of the Cu2Te phase makes the electronic thermal conductivity of the material decrease. At 573 K, the electronic thermal conductivity of the AgCuSb 0.08 Te 0.92 sample is about 0.21 Wm -1 K -1 , which is about 62% lower than that of the pure-phase sample.

[0108] ⑥Thermoelectric figure of merit:

[0109] Figure 13 AgCuTe and AgCuSb obtained by the method of Example 1 x Te 1-x The dimensionless thermoelectric figure of merit (ZT) curve graph. The thermoelectric figure of merit of the material is calculated by ZT = S 2 σT / κ. The thermoelectric figure of merit ZT is directly related to the power factor PF, the thermal conductivity κ, and the temperature T. Figure 13 It shows that doping with Sb element has little improvement 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. Among them, for the AgCuSb 0.08 Te 0.92 sample, the thermoelectric figure of merit reaches 1.28 at 573K, which is about 64% higher than that of the pure phase.

[0110] Table 1 Sample data of Example 1 and Comparative Examples 1 - 2 under the condition of 573K

[0111]

[0112] Table 2 Sample data of Examples 2 - 4 under the condition of 573K

[0113]

[0114] According to the comparative analysis of Example 1 and Comparative Examples 1 - 2, the present invention innovatively uses a one-step direct discharge plasma sintering method to prepare AgCuTe thermoelectric materials, saving preparation energy and time. It omits other pretreatment steps before SPS sintering. For example, the method of the present invention does not require pre-sintering of the sealed tube before SPS sintering, and there is no need to spend a lot of time on the heating and heat preservation operations in the sealed tube (usually about 50h).

[0115] 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, reducing the dependence on the scarce element Te. Sb doping can reduce the diffusion barriers of Ag, Cu, and Te atoms and accelerate element migration. This dynamic diffusion process enables the components to be quickly and evenly distributed during sintering, avoiding the performance degradation caused by composition segregation in traditional processes. The short-time sintering of SPS limits grain growth, while Sb doping forms a pinning effect at the grain boundaries (such as Sb segregation at the grain boundaries), further stabilizing the nanostructure and avoiding grain coarsening caused by traditional long-time pre-sintering.

[0116] In the present invention, Sb doping is selected to inhibit the formation of the Cu2Te phase. Cu2Te is a P-type semiconductor material with a Seebeck coefficient approximately equal to 0 at room temperature, resulting in poor thermoelectric performance and a thermoelectric figure of merit approximately equal to 0. The reduction of the Cu2Te phase changes the performance balance of the mixed-phase composition material, has a small improvement on the electrical properties of the AgCuTe material, but significantly improves its thermal properties, ultimately optimizing the thermoelectric figure of merit of the sample in the entire temperature range of 323 - 573K. With the increase of the Sb element doping amount, 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 that of the pure-phase AgCuTe sample with a thermoelectric figure of merit of 0.78 at this temperature, ranking among the top results of the doping modification research on 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. However, excessive doping may cause the recombination of defects and reduce its thermoelectric performance.

[0117] The present invention utilizes the synergistic effect of the SPS one-step method and Sb doping. By accelerating element diffusion, optimizing the carrier concentration, regulating the microstructure and dynamic reaction path, it successfully replaces the necessity of traditional sealed-tube pre-sintering. 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 new ideas for the development of high-efficiency and low-cost thermoelectric materials.

[0118] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill 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 manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the claims of this patent application.

Claims

1. A preparation method of a thermoelectric material of Sb-doped AgCuTe, characterized in that The chemical formula of the thermoelectric material is AgCuSb x Te 1-x , where x is 0.03 - 0.13; The method includes 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, mix them to obtain the mixed powder A for standby; (2)Add anhydrous ethanol to the mixed powder A and grind it. After the grinding is completed, obtain the mixed powder B; (3)Transfer the mixed powder B into a graphite mold and place it in a spark plasma sintering furnace; (4)Sinter and cool to obtain the thermoelectric material of Sb-doped AgCuTe; In the step (4), the sintering procedure is as follows: start heating from room temperature, start pressurizing while starting heating. After reaching the target temperature and target pressure, perform heat preservation and pressure holding; then relieve the pressure of the mold, and take it out of the mold after cooling to room temperature with the furnace; 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 - 55 MPa, and the pressure increasing rate is 3 - 5 MPa / min; the time for heat preservation and pressure holding is 3 - 5 min; the pressure decreasing rate when relieving the pressure is 0.8 - 1.2 MPa / min.

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

4. The preparation method of the Sb-doped AgCuTe thermoelectric material according to claim 1, characterized in that, In the step (2), the grinding method is: manually grind in a mortar, and the grinding time is 15 - 25 min; the mass ratio of the mixed powder to the volume of anhydrous ethanol is (5 - 5.5) g: 10 mL.

5. The preparation method of the Sb-doped AgCuTe thermoelectric material according to claim 1, characterized in that, In the step (3), the diameter of the graphite mold is 15 mm.

6. The preparation method of the Sb-doped AgCuTe thermoelectric material according to claim 1, characterized in that, In the step (4), the sintering procedure is as follows: start heating from room temperature, the heating rate is 65 °C / min, and the target temperature is 800 °C; the pressure increasing rate is 4 MPa / min, and the target pressure is 50 MPa; the time for heat preservation and pressure holding is 5 min; the pressure decreasing rate when relieving the pressure of the mold is 1 MPa / min.

7. Use of a thermoelectric material of Sb-doped AgCuTe, characterized in that, Apply the thermoelectric material of Sb-doped AgCuTe obtained by the preparation method according to any one of claims 1 - 6 in the working environment of the medium and low temperature region of 300 - 573 K.

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