High-thermoelectric-performance superlattice material and method of making same

Abstract

This invention discloses a superlattice material with high thermoelectric performance and its preparation method, belonging to the field of thermoelectric materials technology. The method includes: [preparing AgSb...] 1‑x Hg x The molar ratio of each element in Se2 is determined by mixing the raw materials, heating, and reacting to obtain a metal ingot. The metal ingot is ground into powder, and a quartz tube containing the metal mixture powder is placed in a vertical single-temperature zone Bridgman furnace for melting and reaction. After the reaction, the temperature is lowered. After cooling, the quartz tube is moved downward to create a temperature difference between its upper and lower ends. Heating in the furnace is stopped, and the temperature is lowered to room temperature. This method allows for the complete melting of the metal raw materials and the directional crystallization growth, resulting in a high-crystallinity superlattice crystal. The prepared superlattice crystal exhibits significantly reduced grain boundary defects, enabling the formation of a superstructure. In Hg-doped AgSbSe2, carrier scattering intensity is significantly reduced, and the influence of impurity scattering is minimized, thus achieving a simultaneous improvement in carrier transport performance and power factor.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials technology, and more specifically, to a superlattice material with high thermoelectric performance and its preparation method. Background Technology

[0002] With the continued advancement of global energy conservation and emission reduction strategies, the demand for high-efficiency energy conversion technologies is becoming increasingly urgent. As an energy utilization method capable of directly exchanging thermal energy for electrical energy, thermoelectric conversion technology is receiving widespread attention worldwide. Thermoelectric materials, with their unique band structure and carrier transport characteristics, can generate thermoelectric potential under temperature difference, thus achieving thermoelectric power generation; conversely, they can establish a temperature difference under the action of an applied current, achieving solid-state refrigeration. Compared with traditional heat engines and refrigeration devices, thermoelectric devices have outstanding advantages such as compact structure, no moving mechanical parts, reliable operation, and adaptability to extreme environments, thus showing significant application prospects in energy recovery, waste heat utilization, deep space exploration power supplies, and small-scale precision refrigeration. However, the large-scale application of thermoelectric technology is still limited by the performance of thermoelectric materials, the core of which is the dimensionless thermoelectric figure of merit (TFP). zT ) Decision, defined as zT = S 2 σT / κ , in S , σ , T and κ These represent the Seebeck coefficient, electrical conductivity, absolute temperature, and total thermal conductivity, respectively, and the power factor (…). PF ), defined as PF = S 2 σ .

[0003] Like classic thermoelectric materials PbTe and AgSbTe2, AgSbSe2 possesses a face-centered cubic structure and does not contain the toxic element lead or the expensive element Te. Benefiting from the disorder of the cation lattice and the influence of lone pair electrons, it exhibits low thermal conductivity, making it a candidate material for mid-temperature thermoelectric power generation. However, the relatively poor electrical properties of AgSbSe2 hinder the improvement of its thermoelectric performance. The structure of disordered cation occupation profoundly affects the electrothermal transport properties of the material. Its advantage lies in exhibiting glass-like thermal conductivity, while its disadvantage is that the stress field changes generated by intrinsic cations and the low carrier mobility caused by intriguing grain boundaries and defects severely impair electrical transport.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a superlattice material with high thermoelectric properties and its preparation method, so as to solve or improve the above-mentioned technical problems.

[0006] This invention can be implemented as follows: In a first aspect, the present invention provides a method for preparing a superlattice material with high thermoelectric properties, comprising the following steps: [preparing a material according to AgSb...] 1-x Hg x The molar ratio of Ag, Sb, Hg and Se in Se2 is determined by mixing silver source, antimony source, mercury source and selenium source, heating and reacting to obtain metal ingots; The metal ingots are ground into powder to obtain a mixed metal powder; A quartz tube containing mixed metal powder is placed in a vertical single-temperature zone Bridgeman furnace for melting reaction. After the reaction is completed, the temperature is lowered. After cooling, the quartz tube is moved downward to create a temperature difference between the upper and lower ends of the quartz tube. The furnace heating is stopped, and the temperature is lowered to room temperature.

[0007] In an optional implementation, 0.01 ≤ x ≤ 0.04.

[0008] In an optional implementation, 0.02 ≤ x ≤ 0.03.

[0009] In an optional implementation, the silver source comprises columnar silver particles; And / or, the antimony source includes antimony spherical particles; And / or, the mercury source includes mercury selenide powder; And / or, the selenium source includes selenium spherical particles; In an optional embodiment, the purity of the silver columnar particles, antimony spherical particles, mercuric selenide powder, and selenium spherical particles is independently ≥99.9%.

[0010] In an optional embodiment, the quartz tube is cylindrical, and the lower end of the quartz tube is conical.

[0011] In an optional implementation, the vacuum level of the quartz tube is ≤10. -5 Pa.

[0012] In an optional implementation, the quartz tube is ultrasonically cleaned before being filled with raw materials.

[0013] In an optional embodiment, the melting reaction is carried out at 950°C to 1050°C for 8 to 12 hours.

[0014] In an optional embodiment, the preparation of the metal ingot includes: heating a silver source, an antimony source, a mercury source, and a selenium source to 500°C to 520°C at a rate of 0.6°C / min to 0.8°C / min, and then heating to 1000°C to 1050°C at a rate of 2°C / min to 2.5°C / min, and holding at that temperature for 8h to 12h.

[0015] In an optional embodiment, a quartz tube containing mixed metal powder is placed in a vertical single-temperature zone Bridgman furnace, and first heated to 500°C to 520°C at a rate of 0.4°C / min to 0.6°C / min and held at that temperature for 3 to 5 hours; then heated to 1100°C to 1150°C at a rate of 0.8°C / min to 1.2°C / min to melt and react for 8 to 12 hours.

[0016] In an alternative implementation, during the melting reaction, the bottom raw material region of the quartz tube is close to the thermocouple of the single-temperature zone Bridgeman furnace.

[0017] In an optional embodiment, the temperature is lowered to 750°C to 760°C after the melting reaction is complete.

[0018] In an optional embodiment, the cooling rate after the melting reaction is completed is 0.4℃ / min to 0.6℃ / min.

[0019] In an optional implementation, the quartz tube descends a distance of 13cm to 15cm.

[0020] In an optional embodiment, the quartz tube moves downward at a speed of 0.35 mm / min to 0.4 mm / min.

[0021] In an optional implementation, the quartz tube descends by 0.04 mm to 0.06 mm each time, and remains at its current position for 6 to 10 seconds after each descent.

[0022] Secondly, the present invention provides a superlattice material with high thermoelectric properties, which is prepared by the above-described preparation method.

[0023] The beneficial effects of this invention include: This invention employs the Bridgman process to grow Hg-doped AgSbSe2 crystals in a controlled temperature field, effectively reducing grain boundary defect density and inducing superlattice formation, thereby obtaining high-quality crystals. In this crystal, the atomic arrangement of the superlattice and the reduction of defects work together to improve carrier mobility and optimize electrical transport performance. Simultaneously, the microstrain generated by the superlattice structure enhances phonon scattering and reduces lattice thermal conductivity, achieving synergistic optimization of electrical and thermal properties. Through this structural control mechanism, high power factors and thermoelectric figures of merit can be achieved over a wide temperature range, thus providing a theoretical and technological basis for the design of high-performance thermoelectric materials. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a diagram illustrating the placement of the raw material in a Bridgeman furnace after vacuum sealing in Example 1. Figure 2 The AgSb prepared in Example 1 1-x Hg x Photograph of Se2 crystal; Figure 3 The AgSb prepared in Example 1 1-x Hg x Selected area electron diffraction pattern of a superlattice in Se2 crystal; Figure 4 The graph shows the relationship between the electrical conductivity of each crystalline material and temperature in Experiment Example 1. Figure 5 The graph shows the Seebeck coefficient of each crystalline material in Experiment Example 1 as a function of temperature. Figure 6 The graph shows the relationship between the power factor of each crystal material and temperature in Experiment Example 1. Figure 7 This is a graph showing the relationship between the total thermal conductivity of each crystalline material and temperature in Experiment Example 1; Figure 8 The graph shows the relationship between the thermoelectric figure of merit of each crystalline material and temperature in Experiment Example 1. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] The following is a detailed description of the cationic short-range ordered and long-range disordered thermoelectric functional crystal and its preparation method provided by the present invention.

[0028] The inventors proposed that the electrothermal transport properties of thermoelectric materials are significantly affected by impurities and grain boundary defects. This invention optimizes thermoelectric performance by reducing crystal defects and forming superlattices. Therefore, this invention provides a method for preparing a high-thermoelectric-performance superlattice material, comprising the following steps: S1: Press AgSb 1-x Hgx The molar ratio of Ag, Sb, Hg and Se in Se2 is determined by mixing silver source, antimony source, mercury source and selenium source, heating and reacting to obtain a metal ingot.

[0029] In some optional embodiments, the silver source includes silver columnar particles; the antimony source includes antimony spherical particles; the mercury source includes mercury selenide powder; and the selenium source includes selenium spherical particles. The purity of the aforementioned silver columnar particles, antimony spherical particles, mercury selenide powder, and selenium spherical particles is independently ≥99.9%. Preferably, the aforementioned high-purity raw materials are weighed in a glove box containing an inert gas (such as argon), thereby effectively preventing the raw materials from reacting with oxygen and moisture in the air, resulting in more accurate composition of the reacting raw materials.

[0030] AgSb 1-x Hg x In Se2, Hg 2+ The radius (102 pm) is between Ag + (11:5pm) and Sb 3+ Within the range of (90 pm), the size mismatch energy of the cation sublattice can be effectively reduced, significantly reducing cation disorder. By doping with Hg, the carrier scattering intensity can be significantly weakened, and the influence of impurity scattering is small, thereby achieving a simultaneous improvement in carrier transport performance and power factor.

[0031] In some alternative implementations, AgSb 1-x Hg x In Se2, x can take values ​​from 0.01 to 0.04, such as 0.01, 0.02, 0.03, or 0.04, or other values ​​within the range of 0.01 to 0.04. In some preferred embodiments, 0.02 ≤ x ≤ 0.03.

[0032] If too little Hg doping is used, it is not conducive to controlling the local structure; if too much Hg doping is used, it is not conducive to suppressing the aggravation of lattice distortion or the formation of secondary phases.

[0033] In some alternative embodiments, the quartz tube is cylindrical, with a pointed, conical lower end to facilitate directional solidification. For example, the inner diameter of the quartz tube can be 13 mm, and the outer diameter can be 16 mm. The apex angle of the pointed end can be 30°, and the length can be 235 mm.

[0034] In some alternative implementations, the vacuum level of the quartz tube is ≤10. -5 Pa, if the vacuum degree of the quartz tube is >10 - 5 Pa is not conducive to inhibiting the volatilization of elements.

[0035] In some alternative implementations, the quartz tube is ultrasonically cleaned before being filled with raw materials to inhibit nucleation on the tube wall.

[0036] In some optional embodiments, the preparation of the metal ingot includes: placing a quartz tube filled with a silver source, an antimony source, a mercury source, and a selenium source in a muffle furnace, and heating it from room temperature to 500°C to 520°C (e.g., 500°C, 510°C, or 520°C) at a rate of 0.6°C / min to 0.8°C / min (e.g., 0.6°C / min, 0.7°C / min, or 0.8°C / min, etc.), and then heating it to 1000°C to 1050°C (e.g., 1000°C, 1020°C, or 1050°C, etc.) at a rate of 2°C / min to 2.5°C / min (e.g., 2°C / min, 2.2°C / min, or 2.5°C / min, etc.), and holding it at this temperature for 8h to 12h (e.g., 8h, 10h, or 12h, etc.) to allow the raw materials to react fully. After the holding period, the muffle furnace is de-energized and cooled to room temperature along with the furnace.

[0037] S2: Grind the metal ingot into powder to obtain a mixed metal powder.

[0038] S3: Place the quartz tube containing the mixed metal powder into a vertical single-temperature zone Bridgeman furnace for melting reaction, and cool down after the reaction is completed; after cooling down, move the quartz tube downward to create a temperature difference between the upper and lower ends of the quartz tube; stop the furnace heating and cool down to room temperature.

[0039] In some alternative embodiments, during the melting reaction, the bottom raw material region of the quartz tube is close to the thermocouple of the single-zone Bridgman furnace. The quartz tube containing the mixed metal powder is placed in a vertical single-zone Bridgman furnace and heated to 500°C to 520°C (e.g., 500°C, 510°C, or 520°C) at a rate of 0.4°C / min to 0.6°C / min (e.g., 0.4°C / min, 0.5°C / min, or 0.6°C / min, etc.) and held at that temperature for 3h to 5h (e.g., 3h, 4h, or 5h, etc.). Subsequently, the temperature is increased to 1100°C to 1150°C (e.g., 1100°C, 1120°C, or 1150°C, etc.) at a rate of 0.8°C / min to 1.2°C / min (e.g., 0.8°C / min, 1°C / min, or 1.2°C / min, etc.) for melting reaction for 8h to 12h (e.g., 8h, 10h, or 12h, etc.).

[0040] By heating in stages, the vapor pressure can be reduced. If the temperature is raised directly to the melting reaction temperature in one go, the quartz tube is prone to cracking.

[0041] In some alternative embodiments, after the melting reaction is completed, the temperature is cooled to 750°C to 760°C, such as 750°C, 755°C, or 760°C, or other values ​​within the range of 750°C to 760°C. The cooling rate after the reaction is completed can be 0.4°C / min to 0.6°C / min, such as 0.4°C / min, 0.5°C / min, or 0.6°C / min, or other values ​​within the range of 0.4°C / min to 0.6°C / min.

[0042] Cooling at a specific rate can help stabilize liquid samples. However, excessively rapid cooling is detrimental to sample stability. Furthermore, cooling to below 750°C or above 760°C after the reaction is complete is also detrimental to sample crystallization.

[0043] In this invention, a common mechanical device can be used to drive the quartz tube downwards, away from the high-temperature center area, so that a temperature difference is formed between the upper and lower ends of the quartz tube.

[0044] In some alternative embodiments, the descent distance of the quartz tube can be 13cm to 15cm, such as 13cm, 13.5cm, 14cm, 14.5cm, or 15cm, or other values ​​within the range of 13cm to 15cm. The quartz tube can move downwards at a speed of 0.35mm / min to 0.4mm / min (such as 0.35mm / min, 0.4mm / min, or 0.45mm / min). The quartz tube descends by 0.04mm to 0.06mm each time (such as 0.04mm, 0.05mm, or 0.06mm), and remains at its current position for 6s to 10s after each descent (such as 6s, 8s, or 10s).

[0045] The descent process of the quartz tube described above can increase the degree of supercooling. Staged descent promotes nucleation of the crystal at the tip. A direct descent of 13-15 cm at once can easily lead to polycrystalline formation. Furthermore, if each descent distance is too short, it is not conducive to obtaining a large degree of supercooling; if each descent distance is too long, it is not conducive to single-nucleation of the sample. In addition, if the total descent distance is less than 13 cm, it is not conducive to crystal growth.

[0046] Continuing from the above, this invention places a sealed quartz tube in a vertical Bridgman furnace and employs a staged heating, holding, and slow cooling temperature program to fully melt the metal raw material and achieve directional crystallization growth. By controlling the cooling and descent rates, high-quality crystals can be obtained. The above process uses the Bridgman method to grow Hg-doped AgSbSe2 crystals in a controlled temperature field, which effectively reduces grain boundary defect density and induces the formation of a superlattice structure, thereby obtaining high-quality crystals. In this crystal, the atomic arrangement of the superlattice and the reduction of defects work together to improve carrier mobility and optimize electrical transport performance. Simultaneously, the microstrain generated by the superlattice structure enhances phonon scattering and reduces lattice thermal conductivity, achieving synergistic optimization of electrical and thermal properties. Through this structural control mechanism, high power factors and thermoelectric figures of merit can be achieved over a wide temperature range, thus providing a theoretical and technological basis for the design of high-performance thermoelectric materials.

[0047] Accordingly, the present invention also provides a superlattice material with high thermoelectric properties, which is prepared by the above-described preparation method.

[0048] The above method addresses the problems of low carrier mobility and poor thermoelectric performance in existing dual-cation thermoelectric semiconductors. By growing high-quality AgSbSe2 crystals without the noble element Te using the Bridgman method, effective grain boundary elimination and superlattice structure control are achieved, significantly increasing carrier mobility and improving thermoelectric performance. Appropriate Hg doping reduces the intensity of atomic electron scattering in the crystal, while impurity scattering does not significantly increase. Both the total carrier scattering potential and the external scattering potential energy are significantly reduced, improving carrier mobility and electrical transport performance. The power factor is approximately three times higher on average than the undoped sample over a wide temperature range, and the thermoelectric figure of merit reaches approximately 1.2 at high temperatures. The p-type single-leg thermoelectric device fabricated based on this crystal achieves an energy conversion efficiency of approximately 6% in the mid-to-high temperature range. This method enables quantitative control of carrier scattering potential, providing a new technical approach for developing high-performance, environmentally friendly thermoelectric materials.

[0049] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0050] Example 1 This embodiment provides a superlattice material with high thermoelectric properties, the preparation method of which includes: S1: In a glove box with an inert gas (argon) protective environment, high-purity (purity not less than 99.99%) silver columnar particles, antimony spherical particles, selenium spherical particles, and mercury selenide powder are mixed according to the AgSb concentration. 1-x Hg xThe molar ratio of elements in Se2 (x=0.01) was accurately measured, and then placed in a cylindrical quartz tube with a pointed lower end (inner diameter 13mm, outer diameter 16mm, cone angle 30°, length 235mm) and sealed under vacuum with a vacuum degree <10. -5 Pa. Then, a quartz tube containing silver, antimony, mercury and selenium sources was placed in a muffle furnace and heated from room temperature to 500°C at a rate of 0.7°C / min, and then to 1000°C at a rate of 2°C / min. The temperature was held for 10 hours, and then the muffle furnace was de-energized and cooled to room temperature to obtain a metal ingot.

[0051] S2: Grind the metal ingot into powder to obtain a mixed metal powder.

[0052] S3: After thoroughly mixing the metal powder, vacuum seal it in a pointed quartz tube (same as S1), and place the quartz tube in a single-temperature zone vertical Bridgman tube furnace (the raw material area at the bottom of the quartz tube is located near the thermocouple of the single-temperature zone vertical Bridgman tube furnace). The furnace temperature is gradually increased to 500℃ at a rate of 0.5℃ / min and held for 4 hours; then, the temperature is increased to 1100℃ at a rate of 1℃ / min for melting reaction for 10 hours. After the melting reaction is completed, the furnace temperature is decreased to 750℃ at a rate of 0.5℃ / min. Subsequently, the position of the quartz tube is gradually moved downward away from the high-temperature center area at a rate of 0.375mm / min, so that a natural temperature difference is formed between the upper and lower ends of the quartz tube (the total downward distance is 14cm, each downward movement is 0.05mm, and the position is held for 8s after each downward movement). After the sample area is completely removed from the furnace, the furnace is stopped heating and slowly cooled to room temperature to obtain a superlattice material with high thermoelectric properties.

[0053] like Figure 1 As shown in the figure, this illustrates the experimental process of sintering superlattice materials in a vertical Bridgman furnace. The figure shows a quartz tube vertically fixed in the center of the furnace cavity, containing a pre-packaged raw material sample. A temperature gradient zone is provided in the lower part of the Bridgman furnace to control the directional solidification of the melt and crystal growth. The operator is adjusting the position of the quartz tube to allow the melt to slowly descend within the temperature gradient, thereby promoting directional crystallization and high-quality crystal growth.

[0054] like Figure 2 As shown in the figure, this is a sample of a superlattice material prepared by the Bridgman process. The crystal is encapsulated in a quartz tube, which is a slender cylinder with a pointed lower end to facilitate directional solidification. A dense, dark gray crystalline region is visible at the bottom of the quartz tube, indicating that the melt underwent a controlled temperature gradient and slow solidification process in the Bridgman furnace, resulting in a uniformly structured and perfectly crystalline AgSb. 1-x Hg xSe2 crystal. This morphological characteristic indicates a stable crystal growth process and high sample quality, which can be used for subsequent structural and electrical transport performance testing.

[0055] like Figure 3 As shown, the figure illustrates along <100> AgSb photographed in crystal orientation 1-x Hg x Selected area electron diffraction (SAED) pattern of Se2 crystal is used to characterize the superlattice structure. The diffraction spots are regularly arranged, showing a well-defined crystal supercell. In addition to the main diffraction spots, additional diffraction spots (circled in red) can be observed at positions such as (0-20), (-2-20), and (-200). These weak reflection peaks originate from periodic cell expansion.

[0056] Example 2 The difference between this embodiment and Embodiment 1 is that AgSb 1-x Hg x In Se2, x = 0.02.

[0057] Example 3 The difference between this embodiment and Embodiment 1 is that AgSb 1-x Hg x In Se2, x = 0.03.

[0058] Example 4 The difference between this embodiment and Embodiment 1 is that AgSb 1-x Hg x In Se2, x = 0.04.

[0059] Example 5 The difference between this embodiment and Embodiment 1 is that AgSb 1-x Hg x In Se2, x = 0.05.

[0060] Example 6 This embodiment provides a superlattice material with high thermoelectric properties, the preparation method of which includes: S1: In a glove box with an inert gas (argon) protective environment, high-purity (purity not less than 99.99%) silver columnar particles, antimony spherical particles, selenium spherical particles, and mercury selenide powder are mixed according to the AgSb concentration. 1-x Hg x The molar ratio of elements in Se2 (x=0.02) is accurately measured, and after weighing, it is placed in a cylindrical quartz tube at the bottom and vacuum-sealed with a vacuum degree <10. -5Pa. Then, a quartz tube containing silver, antimony, mercury and selenium sources was placed in a muffle furnace and heated from room temperature to 510°C at a rate of 0.6°C / min, and then to 1020°C at a rate of 2°C / min. The temperature was held for 12 hours, and then the muffle furnace was de-energized and cooled to room temperature to obtain a metal ingot.

[0061] S2: Grind the metal ingot into powder to obtain a mixed metal powder.

[0062] S3: After thoroughly mixing the metal powder, vacuum seal it in a pointed quartz tube (same as S1), and place the quartz tube in a single-temperature zone vertical Bridgman tube furnace (the raw material area at the bottom of the quartz tube is located near the thermocouple of the single-temperature zone vertical Bridgman tube furnace). The furnace temperature is gradually increased to 510℃ at a rate of 0.4℃ / min and held for 5 hours; then, the temperature is increased to 1120℃ at a rate of 0.8℃ / min for a melting reaction for 12 hours. After the melting reaction is completed, the furnace temperature is decreased to 755℃ at a rate of 0.4℃ / min. Subsequently, the position of the quartz tube is gradually moved downward away from the high-temperature center area at a rate of 0.35mm / min, so that a natural temperature difference is formed between the upper and lower ends of the quartz tube (the total downward distance is 13cm, each downward movement is about 0.04mm, and the position is held for 6s after each downward movement). After the sample area is completely removed from the furnace, the furnace is stopped heating and slowly cooled to room temperature to obtain a superlattice material with high thermoelectric properties.

[0063] Example 7 This embodiment provides a superlattice material with high thermoelectric properties, the preparation method of which includes: S1: In a glove box with an inert gas (argon) protective environment, high-purity (purity not less than 99.99%) silver columnar particles, antimony spherical particles, selenium spherical particles, and mercury selenide powder are mixed according to the AgSb concentration. 1-x Hg x The molar ratio of elements in Se2 (x=0.02) was accurately measured, and after weighing, the sample was placed in a cylindrical quartz tube and vacuum-sealed with a vacuum degree <10. -5 Pa. Then, a quartz tube containing silver, antimony, mercury and selenium sources was placed in a muffle furnace. The temperature was first increased from room temperature to 520°C at a rate of 0.8°C / min, and then increased to 1050°C at a rate of 2.5°C / min. The temperature was held for 8 hours, and then the muffle furnace was de-energized and cooled to room temperature to obtain a metal ingot.

[0064] S2: Grind the metal ingot into powder to obtain a mixed metal powder.

[0065] S3: After thoroughly mixing the metal powder, vacuum seal it in a pointed quartz tube (same as S1), and place the quartz tube in a single-temperature zone vertical Bridgman tube furnace (the raw material area at the bottom of the quartz tube is located near the thermocouple of the single-temperature zone vertical Bridgman tube furnace). The furnace temperature is gradually increased to 520℃ at a rate of 0.6℃ / min and held for 4 hours; then, the temperature is increased to 1150℃ at a rate of 1.2℃ / min for melting reaction for 8 hours. After the melting reaction is completed, the furnace temperature is decreased to 760℃ at a rate of 0.6℃ / min. Subsequently, the position of the quartz tube is gradually moved downward away from the high-temperature center area at a rate of 0.4mm / min, so that a natural temperature difference is formed between the upper and lower ends of the quartz tube (the total downward distance is 15cm, each downward movement is about 0.06mm, and the position is held for 10s after each downward movement). After the sample area is completely removed from the furnace, the furnace is stopped heating and slowly cooled to room temperature to obtain a superlattice material with high thermoelectric properties.

[0066] Comparative Example 1 This comparative example provides a high thermoelectric superlattice material, prepared as follows: In a glove box with an inert gas (argon) protective environment, high-purity (purity not less than 99.99%) silver columnar particles, antimony spherical particles, and selenium spherical particles were precisely weighed according to the stoichiometric ratio AgSbSe2. After weighing, the raw materials were placed in a quartz tube and vacuum sealed. The quartz tube containing the raw materials was placed in a muffle furnace, and the furnace temperature was gradually increased to 500℃ at a rate of 0.7℃ / min. Then, the muffle furnace temperature was increased to 1000℃ at a rate of 2℃ / min and held for 10 hours before cooling with the furnace. The resulting ingot was ground into a fine powder and then hot-pressed under vacuum conditions (750K, 45MPa, holding for 60min) to form a dense cylindrical sample, which was then slowly cooled with the furnace. The hot-pressed sample was then cut into appropriate sizes for different performance tests.

[0067] Comparative Example 2 The difference between this comparative example and Example 1 is that: AgSb 1-x Hg x In Se2, x=0, and the final material is a single crystal.

[0068] Experimental Example 1 The properties of the final crystal materials prepared in Examples 1-5 and Comparative Examples 1-2 were compared, and the results are as follows: Figures 4 to 8 As shown. Figures 4 to 8 Curves of the same color in the diagram correspond to the same crystal material; see [link to specific correspondences] for details. Figure 4 The middle mark.

[0069] like Figure 4As shown in the figure, this graph illustrates the relationship between the electrical conductivity (σ) of each crystalline material and temperature. The horizontal axis represents temperature (K), and the vertical axis represents electrical conductivity (S / cm). The polycrystalline AgSbSe2 sample (Comparative Example 1) exhibits higher electrical conductivity throughout the entire test temperature range, while the single-crystal AgSbSe2 (Comparative Example 2) has lower electrical conductivity, which increases slightly with increasing temperature. This is mainly attributed to the more complete lattice structure and fewer cation defects in single-crystal AgSbSe2, resulting in a lower carrier concentration. Hg-doped AgSb 1-x Hg x The Se2 crystal samples (Examples 1-5) exhibited significantly enhanced electrical conductivity, with the highest conductivity observed at x=0.03. This indicates that appropriate Hg doping can effectively improve electrical transport performance by adjusting the carrier concentration. Overall, Hg doping promotes carrier generation and migration, maintaining a high level of conductivity over a wide temperature range, thus providing a foundation for improved thermoelectric performance.

[0070] like Figure 5 As shown in the figure, this graph illustrates the relationship between the Seebeck coefficient of each crystal material and temperature. The horizontal axis represents temperature (K), and the vertical axis represents the Seebeck coefficient S (μV / K). It can be seen from the figure that the undoped Hg AgSbSe2 single crystal (Comparative Example 2) has the highest Seebeck coefficient at room temperature, approximately 800 μV / K, and gradually decreases with increasing temperature, exhibiting typical... p The behavior of Hg-doped AgSb. 1-x Hg x The Se2 crystal sample exhibits a relatively low Seebeck coefficient across the entire temperature range, but its value increases slightly with increasing temperature, showing a temperature dependence trend opposite to that of the undoped sample.

[0071] like Figure 6 As shown, this figure illustrates the power factor of each crystal material. PF The relationship between temperature and power factor. The horizontal axis represents temperature (K), and the vertical axis represents the power factor. PF (μW / (cm·K) 2 The undoped AgSbSe2 single crystal sample (Comparative Example 2) had the lowest power factor, while the Hg-doped samples (Examples 1-5) showed a significant increase in power factor, indicating that the carrier transport performance was effectively optimized. In particular, the x=0.02 crystal exhibited the highest power factor across the entire temperature range. PF The value reaches 7.15 μW / (cm·K) at 723 K. 2 Compared to the polycrystalline AgSbSe2 sample (Comparative Example 1, 2.44 μW / (cm·K)), 2 It increases by about 3 times.

[0072] like Figure 7 As shown in the figure, this graph illustrates the total thermal conductivity of each crystalline material. κ tot The relationship between temperature and thermal conductivity is shown. The horizontal axis represents temperature (K), and the vertical axis represents total thermal conductivity (W / (m·K)). The total thermal conductivity of all samples gradually decreases with increasing temperature, exhibiting a typical phonon-dominated thermal conductivity characteristic. Compared with polycrystalline AgSbSe2 (Comparative Example 1), the total thermal conductivity of the Hg-doped crystal sample is slightly increased throughout the temperature range. This is mainly due to the significant increase in its electrical conductivity, which leads to an increase in electronic thermal conductivity.

[0073] like Figure 8 As shown in the figure, this graph illustrates the dimensionless thermoelectric figure of merit for each crystalline material. zT The relationship between temperature and temperature. The horizontal axis represents temperature (K), and the vertical axis represents... zT Values. All samples zT The values ​​all increase with increasing temperature, exhibiting typical temperature-dependent characteristics of thermoelectric materials. Undoped AgSbSe2 single crystal (Comparative Example 2) zT The value was lower, while the Hg-doped samples (Examples 1-5) showed a lower value. zT The value was significantly improved. Among them, the crystal corresponding to x=0.02 in Example 2 exhibited the best thermoelectric performance at 723K. zT The value is as high as 1.2, averaging over a temperature range of 323K to 723K. zT The value reached 0.7. This result demonstrates that the high-quality Hg-doped AgSbSe2 crystals prepared by the Bridgman method have significant advantages in achieving a balance between carrier transport and thermal conductivity, providing a feasible structural control strategy for developing efficient, tellurium-free thermoelectric materials.

[0074] Experimental Example 2 This experiment included control examples 1-11, among which: The difference between Comparative Example 1 and Example 2 is that AgSb 1-x Hg x In Se2, x=0, and the third step of Bridgman vertical descent growth was not performed.

[0075] The difference between Comparative Example 2 and Example 2 is that AgSb 1-x Hg x In Se2, x=0. This is also the comparative example 2 in experimental example 1.

[0076] The difference between Comparative Example 3 and Example 2 is that the lower end of the quartz tube is horizontal.

[0077] The difference between Comparative Example 4 and Example 2 is that the temperature is directly raised to 1000°C in one go during the melting reaction process.

[0078] The difference between Comparative Example 5 and Example 2 is that during the melting reaction, the temperature was increased to 1100°C at a heating rate of 1.5°C / min.

[0079] The difference between Comparative Example 6 and Example 2 is that after the reaction is completed, the temperature is directly reduced to 750°C in one go.

[0080] The difference between Comparative Example 7 and Example 2 is that the cooling rate after the reaction is completed is 1℃ / min.

[0081] The difference between Comparative Example 8 and Example 2 is that the quartz tube was not moved downwards after cooling.

[0082] The difference between Comparative Example 9 and Example 2 is that after cooling, the quartz tube moves downward at a rate of 0.45 mm / min.

[0083] The difference between Comparative Example 10 and Example 2 is that after cooling, the quartz tube moves downward a total distance of 10cm.

[0084] The difference between Comparative Example 11 and Example 2 is that Cu element is used to replace Hg in equal amounts.

[0085] The crystal materials prepared in Examples 6-7 and Comparative Examples 1-11 were tested according to the method of Experimental Example 1. The test results are shown in Table 1.

[0086] Table 1 Test Results (723 K)

[0087] As can be seen from Table 1, compared with Comparative Examples 1 to 11, the crystal materials prepared by the method provided in the embodiments of the present invention have better overall performance in terms of the above-mentioned properties.

[0088] In summary, this invention utilizes the Bridgman method to grow high-quality AgSbSe2 crystals free of the noble element Te, achieving effective elimination of grain boundaries and control of the superlattice structure, thereby significantly increasing carrier mobility and improving thermoelectric performance. Appropriate Hg doping reduces the intensity of atomic electron scattering in the crystal, while impurity scattering does not significantly increase. Both the total carrier scattering potential and the external scattering potential energy are significantly reduced, improving carrier mobility and electrical transport performance. The power factor is approximately three times higher on average than the undoped sample over a wide temperature range, and the thermoelectric figure of merit reaches approximately 1.2 at high temperatures. The p-type single-leg thermoelectric device fabricated based on this crystal achieves an energy conversion efficiency of approximately 6% in the mid-to-high temperature range. This method enables quantitative control of carrier scattering potential, providing a new technical approach for developing high-performance, environmentally friendly thermoelectric materials.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a superlattice material with high thermoelectric properties, characterized in that, Includes the following steps: Press AgSb 1- x Hg x The molar ratio of Ag, Sb, Hg and Se in Se2 is determined by mixing silver source, antimony source, mercury source and selenium source, heating and reacting to obtain metal ingots; The metal ingot is ground into powder to obtain a metal mixed powder; The quartz tube containing the metal mixed powder is placed in a vertical single-temperature zone Bridgeman furnace for melting reaction. After the reaction is completed, the temperature is lowered. After cooling, the quartz tube is moved downward to create a temperature difference between the upper and lower ends of the quartz tube. The furnace heating is stopped, and the temperature is lowered to room temperature.

2. The preparation method according to claim 1, characterized in that, 0.01≤x≤0.04； Preferably, 0.02 ≤ x ≤ 0.03; And / or, the silver source comprises columnar silver particles; And / or, the antimony source comprises antimony spherical particles; And / or, the mercury source includes mercury selenide powder; And / or, the selenium source comprises selenium spherical particles.

3. The preparation method according to claim 1, characterized in that, The quartz tube is cylindrical, and the lower end of the quartz tube is conical.

4. The preparation method according to claim 1, characterized in that, The vacuum degree of the quartz tube is ≤10. -5 Pa; Preferably, the quartz tube is ultrasonically cleaned before being filled with raw materials.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The preparation of the metal ingot includes: heating the silver source, the antimony source, the mercury source, and the selenium source to 500℃~520℃ at a rate of 0.6℃ / min~0.8℃ / min, and then heating them to 1000℃~1050℃ at a rate of 2℃ / min~2.5℃ / min, and holding them at that temperature for 8h~12h.

6. The preparation method according to any one of claims 1 to 4, characterized in that, The quartz tube containing the metal mixed powder was placed in a vertical single-temperature zone Bridgman furnace. The temperature was first increased to 500℃~520℃ at a rate of 0.4℃ / min~0.6℃ / min and held for 3h~5h. Then the temperature was increased to 1100℃~1150℃ at a rate of 0.8℃ / min~1.2℃ / min and melted for 8h~12h.

7. The preparation method according to claim 6, characterized in that, During the melting reaction, the bottom raw material area of ​​the quartz tube is close to the thermocouple of the single-temperature zone Bridgeman furnace; And / or, after the melting reaction is complete, cool down to 750℃~760℃; Preferably, the cooling rate after the melting reaction is completed is 0.4℃ / min to 0.6℃ / min.

8. The preparation method according to claim 1, characterized in that, The descent distance of the quartz tube is 13cm~15cm; Preferably, the quartz tube moves downward at a speed of 0.35 mm / min to 0.4 mm / min.

9. The preparation method according to claim 1, characterized in that, The quartz tube descends by 0.04mm to 0.06mm each time, and remains at its current position for 6s to 10s after each descent.

10. A superlattice material with high thermoelectric properties, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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