Porous germanium telluride thermoelectric material and preparation method thereof

Abstract

The invention belongs to the field of germanium telluride thermoelectric materials, and particularly relates to a porous germanium telluride thermoelectric material and a preparation method thereof. The method comprises the following steps: carrying out ball milling on a simple substance powder raw material and fluoride to obtain mixed powder; sintering the mixed powder to obtain a germanium telluride thermoelectric material preform; and performing annealing treatment on the germanium telluride thermoelectric material preform to obtain the porous germanium telluride thermoelectric material. The preparation method is simple to operate and easy to implement, impurities are not introduced, and the porosity can be regulated and controlled; the porous germanium telluride thermoelectric material obtained by the preparation method has excellent thermoelectric performance and high thermoelectric figure of merit.

Description

Technical Field

[0001] This application belongs to the field of germanium telluride thermoelectric materials, specifically relating to porous germanium telluride thermoelectric materials and their preparation methods. Background Technology

[0002] In the application of germanium telluride thermoelectric materials, reducing heat conduction loss is key to improving their thermoelectric performance, which requires germanium telluride thermoelectric materials to have a low lattice thermal conductivity (kJ / kt). L The lattice thermal conductivity (k) and total thermal conductivity (κ) are related. Lattice thermal conductivity is negatively correlated with phonon scattering; therefore, by introducing a porous structure into the germanium telluride system and utilizing the pore interfaces as phonon scattering centers, the phonon scattering effect can be significantly enhanced, thereby reducing the lattice thermal conductivity (k). L The porous structure can reduce the material density, further contributing to the decrease in lattice thermal conductivity and total thermal conductivity. Currently, the introduction of porous structures mainly relies on organic pore-forming agents or excessive germanium volatilization. However, the former is prone to uneven distribution of pores due to uneven distribution of the pore-forming agent, while the latter is limited by the germanium volatilization efficiency, making it difficult to achieve high porosity control. Moreover, both methods may introduce residual impurities or damage the matrix structure, ultimately limiting the thermoelectric performance and application scenarios of germanium telluride thermoelectric materials. Therefore, it is urgent to develop a preparation method with controllable porosity that does not introduce impurities. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in related technologies. To this end, the present invention proposes a porous germanium telluride thermoelectric material and its preparation method. This preparation method is simple to operate, easy to implement, does not introduce impurities, and allows for controllable porosity. The porous germanium telluride thermoelectric material obtained by this preparation method exhibits excellent thermoelectric properties and a high thermoelectric figure of merit.

[0004] A first aspect of this application provides a method for preparing porous germanium telluride thermoelectric materials, comprising: ball milling elemental powder raw materials and fluoride to obtain a mixed powder; sintering the mixed powder to obtain a germanium telluride thermoelectric material preform; and annealing the germanium telluride thermoelectric material preform to obtain a porous germanium telluride thermoelectric material.

[0005] Therefore, compared to related technologies that use organic pore-forming agents or excessive germanium volatilization to prepare porous germanium telluride thermoelectric materials, this method has significant advantages in introducing fluorides into the preparation of porous germanium telluride thermoelectric materials. This method is simple to operate, easy to implement, does not introduce impurities, and allows for precise control of the porosity of the porous germanium telluride thermoelectric material by adjusting the amount of fluoride added. Simultaneously, the metal elements remaining after fluoride decomposition can be incorporated into the germanium telluride lattice, thereby optimizing the thermoelectric performance of the porous germanium telluride thermoelectric material.

[0006] According to embodiments of this application, the fluoride includes at least one of bismuth trifluoride, cuprous fluoride, and silver hexafluoroantimonate, specifically bismuth trifluoride. Thus, the fluoride thermally decomposes at high temperatures to generate F2 gas, which escapes and forms pores. Simultaneously, the metal element generated during decomposition can be incorporated into the germanium telluride lattice as a dopant, avoiding the presence of foreign impurities and optimizing the thermoelectric performance of the germanium telluride thermoelectric material through metal doping.

[0007] According to embodiments of this application, the elemental powder raw material satisfies any one of the following: the elemental powder raw material includes Ge elemental powder and Te elemental powder; the elemental powder raw material includes Ge elemental powder, Te elemental powder and Bi elemental powder; the elemental powder raw material includes Ge elemental powder, Te elemental powder and Cu elemental powder; the elemental powder raw material includes Ge elemental powder, Te elemental powder, Bi elemental powder and Cu elemental powder. Therefore, the porous germanium telluride thermoelectric material can be either a germanium telluride thermoelectric material containing only Ge and Te, or a germanium telluride thermoelectric material doped with at least one element from Bi and Cu, thus having a wide range of applications.

[0008] According to embodiments of this application, the elemental powders satisfy any one of the following conditions: the molar ratio of Ge elemental powder to Te elemental powder is 0.93-0.98:1; the molar ratio of Ge elemental powder, Te elemental powder, and Bi elemental powder is 0.93-0.98:1:0.02-0.07; the molar ratio of Ge elemental powder, Te elemental powder, and Cu elemental powder is 0.93-0.98:1:0-0.03; and the molar ratio of Ge elemental powder, Te elemental powder, Bi elemental powder, and Cu elemental powder is 0.93-0.98:1:0.02-0.07:0-0.03. Therefore, within the above molar ratio ranges, the carrier concentration can be better adjusted, thereby optimizing the thermoelectric performance of the germanium telluride thermoelectric material.

[0009] According to embodiments of this application, the ball mill satisfies at least one of the following conditions: the ball-to-material ratio is 10-30:1; the ball mill rotation speed is 300 r / min-500 r / min; and the ball milling time is 2 h-12 h. Therefore, during the ball milling process, a suitable ball-to-material ratio, rotation speed, and milling time ensure sufficient collision frequency between the grinding balls and the raw material, which helps to fully refine the raw material, enabling uniform mixing and improving grinding efficiency.

[0010] According to embodiments of this application, the sintering process satisfies at least one of the following conditions: the vacuum degree of the sintering is 0.1 Pa-10 Pa; the heating rate of the sintering is 20 °C / min-100 °C / min; the sintering temperature is 400 °C-650 °C; the sintering pressure is 20 MPa-60 MPa; and the sintering time is 5 min-30 min. Therefore, suitable vacuum degree, heating rate, sintering temperature, sintering pressure, and sintering time can ensure that the mixed powder is heated more uniformly during the sintering process, improving the uniformity and density of the porous germanium telluride thermoelectric material.

[0011] According to embodiments of this application, the annealing satisfies at least one of the following conditions: the annealing temperature is 400℃-550℃; the annealing time is 6h-8h. Thus, suitable annealing temperature and annealing time can eliminate residual internal stress in the germanium telluride thermoelectric material preform during sintering, and reduce dislocation defects and microcracks.

[0012] In a second aspect, this application provides a porous germanium telluride thermoelectric material prepared according to the method described above. The parameters and characteristics of this porous germanium telluride thermoelectric material are consistent with those in the preparation method described above, and will not be repeated here.

[0013] According to an embodiment of this application, the chemical composition of the germanium telluride thermoelectric material is Bi. x+z Ge 0.98-x-z TeCu y M z Where M includes fluorides, 0.02≤x≤0.07, 0≤y≤0.03, 0≤z≤0.01, and specifically z can be 0<z≤0.01. Therefore, porous germanium telluride thermoelectric materials with the above composition exhibit good crystallinity and high structural density; simultaneously, they possess a high power factor and low lattice thermal conductivity, resulting in a high thermoelectric figure of merit.

[0014] According to embodiments of this application, the porosity of the porous germanium telluride thermoelectric material is 5%-25%. A suitable porosity provides a sufficient number of phonon scattering centers, enhancing the phonon scattering effect, thereby reducing lattice thermal conductivity and thermal conductivity, and improving the thermoelectric figure of merit. Furthermore, a suitable porosity maintains a certain level of mechanical strength. Attached Figure Description

[0015] Figure 1 These are the X-ray diffraction patterns of the porous germanium telluride thermoelectric materials of Examples 1 and 2 of this application.

[0016] Figure 2 These are scanning electron microscope images of the porous germanium telluride thermoelectric materials of Examples 1 to 3 of this application.

[0017] Figure 3 These are transmission electron microscope images of the porous germanium telluride thermoelectric materials of Examples 1 and 3 of this application.

[0018] Figure 4 This is a graph showing the conductivity test results of the porous germanium telluride thermoelectric material of Comparative Example 1 and Examples 1 to 3 of this application.

[0019] Figure 5 The Seebeck coefficient test results are shown for the porous germanium telluride thermoelectric materials of Comparative Example 1 and Examples 1 to 3 of this application.

[0020] Figure 6 This is a graph showing the power factor test results of the porous germanium telluride thermoelectric material of Comparative Example 1 and Examples 1 to 3 of this application.

[0021] Figure 7 The graph shows the thermal conductivity test results of the porous germanium telluride thermoelectric materials of Comparative Example 1 and Examples 1 to 3 of this application.

[0022] Figure 8 The graph shows the electronic thermal conductivity test results of the porous germanium telluride thermoelectric materials of Comparative Example 1 and Examples 1 to 3 of this application.

[0023] Figure 9 The graph shows the lattice thermal conductivity test results of the porous germanium telluride thermoelectric materials of Comparative Example 1 and Examples 1 to 3 of this application.

[0024] Figure 10 The graph shows the thermoelectric figure of merit test results of the porous germanium telluride thermoelectric materials of Comparative Example 1 and Examples 1 to 3 of this application. Detailed Implementation

[0025] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0026] A first aspect of this application provides a method for preparing porous germanium telluride thermoelectric materials, the method comprising:

[0027] S10: Ball mill the elemental powder raw material and the fluoride to obtain a mixed powder.

[0028] In this step, the elemental powder raw material and fluoride are continuously broken down during the ball milling process, forming particles with a size of micrometers or even nanometers. The ball milling process promotes the full mixing of particles of different elements, forming a uniform mixed powder.

[0029] Ball milling fluorides directly with elemental raw materials is simple, quick, poses no high-temperature hazard, and consumes little energy, making it suitable for large-scale preparation.

[0030] According to embodiments of this application, the fluoride includes at least one of bismuth trifluoride, cuprous fluoride, and silver hexafluoroantimonate. In some embodiments, bismuth trifluoride is used as the fluoride. Thus, the fluoride thermally decomposes at high temperature to generate F2 gas, which escapes and forms pores. Simultaneously, the metal element generated from the decomposition of the fluoride can be incorporated into the germanium telluride lattice as a dopant, further optimizing the thermoelectric performance of the porous germanium telluride thermoelectric material through metal doping.

[0031] It is understood that there are no restrictions on the specific constituent elements of porous germanium telluride thermoelectric materials. They can be porous germanium telluride thermoelectric materials containing only Ge and Te, or they can be porous germanium telluride thermoelectric materials doped with at least one element selected from Bi and Cu. In some embodiments, the constituent elements of the porous germanium telluride thermoelectric material are Ge, Te, Bi, and Cu.

[0032] According to some embodiments of this application, the elemental powder raw materials include Ge elemental powder and Te elemental powder. Thus, the above composition can form the main crystal lattice structure of a porous germanium telluride thermoelectric material matrix.

[0033] According to embodiments of this application, the molar ratio of Ge elemental powder to Te elemental powder is 0.93-0.98:1, specifically 0.93:1, 0.94:1, 0.95:1, 0.96:1, 0.97:1, 0.98:1, or any range between two of these. Within this ratio range, it is beneficial to generate a structure with GeTe as the main phase, which helps maintain the stability of the porous germanium telluride thermoelectric material. If the ratio is too high, i.e., Ge is excessive, it may lead to the formation of the Ge2Te3 impurity phase, reducing the thermoelectric figure of merit of the porous germanium telluride thermoelectric material; if the ratio is too low, i.e., Te is excessive, it may lead to the precipitation of elemental Te, resulting in an inhomogeneous structure of the porous germanium telluride thermoelectric material and reducing its thermoelectric performance.

[0034] According to some other embodiments of this application, the elemental powder raw materials include Ge elemental powder, Te elemental powder, and Bi elemental powder. Thus, doping Bi element in porous germanium telluride thermoelectric materials can introduce lattice distortion, enhance phonon scattering, and reduce lattice thermal conductivity and thermal conductivity.

[0035] In this paper, the lattice thermal conductivity (k) L The lattice vibration contribution to heat conduction in germanium telluride thermoelectric materials describes the material's ability to conduct heat through lattice vibrations. It can be calculated using the Weidmann-Frantz formula.

[0036] Thermal conductivity (κ) refers to the amount of heat passing through a unit area of ​​a thermoelectric material per unit time under a unit temperature gradient. It includes both electronic thermal conductivity and lattice thermal conductivity, and is a physical quantity describing the thermal conductivity of germanium telluride thermoelectric materials. It can be calculated by combining the thermal diffusivity obtained from the Nitzer LFA457 tester with the sample's heat capacity and density.

[0037] According to embodiments of this application, the molar ratio of Ge elemental powder, Te elemental powder, and Bi elemental powder is 0.93-0.98:1:0.02-0.07, specifically 0.93:1:0.07, 0.94:1:0.06, 0.95:1:0.05, 0.96:1:0.04, 0.97:1:0.03, 0.98:1:0.02, or any two of these ranges. Thus, within the above ratio range, a small amount of Bi, as a dopant element, enters the germanium telluride lattice, which can regulate the carrier concentration and optimize the thermoelectric performance of the porous germanium telluride thermoelectric material. If the ratio is too high, it may lead to insufficient carrier concentration and reduced conductivity; if the ratio is too low, it may lead to the formation of impurity phases, affecting the structural stability of the porous germanium telluride thermoelectric material.

[0038] According to some embodiments of this application, the elemental powder raw materials include Ge elemental powder, Te elemental powder, and Cu elemental powder. Thus, Cu can be uniformly dispersed in the lattice of the porous germanium telluride thermoelectric material, enhancing phonon scattering to reduce lattice thermal conductivity, while simultaneously adjusting carrier concentration and improving the thermoelectric figure of merit.

[0039] In this paper, the thermoelectric figure of merit (ZT) is a dimensionless parameter that measures the performance of thermoelectric materials and is used to evaluate the efficiency with which thermoelectric materials convert thermal energy into electrical energy. Its expression is: ZT = σS 2 T / κ, where σ is the electrical conductivity, S is the Seebeck coefficient, T is the absolute temperature, κ is the thermal conductivity, and σS 2 This is the power factor.

[0040] According to embodiments of this application, the molar ratio of Ge elemental powder, Te elemental powder, and Cu elemental powder is 0.93-0.98:1:0-0.03, specifically 0.93:1:0, 0.95:1:0.02, 0.98:1:0.03, or any range between two of these. Therefore, within the above ratio range, a small amount of Cu, as a dopant element, enters the germanium telluride lattice, which can control the carrier concentration and optimize the thermoelectric performance of the porous germanium telluride thermoelectric material. If the ratio is too high, it may lead to insufficient carrier concentration and reduced conductivity; if the ratio is too low, it may lead to the formation of impurity phases, affecting the structural stability of the porous germanium telluride thermoelectric material.

[0041] According to further embodiments of this application, the elemental powder raw materials include Ge elemental powder, Te elemental powder, Bi elemental powder, and Cu elemental powder. Thus, the simultaneous introduction of Cu and Bi can both enhance phonon scattering and reduce thermal conductivity, and precisely control the carrier concentration through dual-element doping, thereby improving the thermoelectric figure of merit of the porous germanium telluride thermoelectric material.

[0042] According to embodiments of this application, the molar ratio of Ge elemental powder, Te elemental powder, Bi elemental powder, and Cu elemental powder is 0.93-0.98:1:0.02-0.07:0-0.03, specifically 0.93:1:0.02:0, 0.94:1:0.03:0.01, 0.95:1:0.04:0.02, 0.98:1:0.07:0.03, or any range between two of these. Therefore, within the above ratio range, a small amount of Bi and Cu doping can effectively control the carrier concentration, reduce the lattice thermal conductivity, and optimize the thermoelectric performance of the porous germanium telluride thermoelectric material. If the ratio is too high, it may lead to insufficient carrier concentration and reduced conductivity; if the ratio is too low, it may lead to the formation of impurity phases, affecting the structural stability of the porous germanium telluride thermoelectric material.

[0043] According to embodiments of this application, the ball-to-material ratio of the ball mill is 20-30:1, specifically 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, or any range between two of these. As a specific example, the ball-to-material ratio is 25:1. Therefore, a suitable ball-to-material ratio ensures sufficient collision frequency between the grinding balls and the raw material, contributing to uniform mixing and improving grinding efficiency. If the ball-to-material ratio is too low, the contact frequency between the raw material and the grinding balls decreases, resulting in insufficient grinding force and potentially uneven mixing. If the ball-to-material ratio is too high, excessive grinding balls may restrict the movement of the grinding balls, reducing effective collisions between the grinding balls and the raw material, and lowering the ball milling efficiency.

[0044] According to embodiments of this application, the rotational speed of the ball mill is 300 r / min to 500 r / min, specifically 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, or any range between two of these. As a specific example, the rotational speed of the ball mill is 450 r / min. Therefore, within the aforementioned rotational speed range, the grinding balls can generate strong impact and frictional forces, thereby effectively reducing the size of the raw material. If the rotational speed is too low, the raw material may not be sufficiently ground, resulting in larger particle sizes; if the rotational speed is too high, it will exacerbate the wear of the grinding balls and shorten the lifespan of the ball mill equipment.

[0045] According to embodiments of this application, the ball milling time is 8-16 hours, specifically 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, or any range between two of these. As a specific example, the ball milling time is 12 hours. Therefore, an appropriate ball milling time ensures that the raw materials are sufficiently refined, contributing to uniform mixing. Too short a ball milling time may result in insufficient refinement and mixing of the raw materials; too long a ball milling time may lead to over-refinement and agglomeration of the raw materials.

[0046] According to embodiments of this application, the ball milling process further includes introducing a protective gas, which includes an inert gas. In some embodiments, the inert gas may be an argon-hydrogen mixture (hydrogen volume content of 5% and argon volume content of 95%). Thus, adding a small amount of hydrogen to the protective gas can consume the oxygen in the equipment, ensuring that the ball milling process is always in an oxygen-free environment.

[0047] According to embodiments of this application, the grinding balls used in the ball milling process have a diameter of at least one selected from 10mm, 6mm, and 4mm. In some embodiments, grinding balls with diameters of 10mm, 6mm, and 4mm can be added simultaneously. Thus, grinding balls of different diameters generate different impact forces and grinding effects during the ball milling process, colliding and compressing each other, increasing the contact frequency between the grinding media and the raw material, thereby improving grinding efficiency.

[0048] As a specific example, elemental powders of Ge, Te, Bi, and Cu, along with fluoride, were weighed and ball-milled. Grinding balls with diameters of 10 mm, 6 mm, and 4 mm were added, with a mass ratio of grinding balls to raw materials of 20-30:1. An argon-hydrogen mixture was used as a protective gas (hydrogen volume content of 5% and argon volume content of 95%). The mixture was ball-milled at a speed of 300 r / min-500 r / min for 8-12 hours.

[0049] S20: The mixed powder is sintered to obtain a germanium telluride thermoelectric material preform.

[0050] In this step, during the sintering process, the mixed powder particles undergo diffusion and chemical reaction to form a germanium telluride matrix and related compound phases; Bi is doped into the germanium telluride matrix, accompanied by grain growth and densification, the interface between powder particles disappears, and a germanium telluride thermoelectric material preform is formed through grain boundary migration and mass migration; at the same time, fluoride decomposes during the sintering process to generate F2 gas, and some of the gas escapes rapidly at high temperature to form a porous structure.

[0051] According to embodiments of this application, the sintering method includes at least one of discharge plasma sintering and hot pressing sintering. As an example, this application uses discharge plasma for sintering. This results in lower energy consumption, eliminates the need for complex sintering atmosphere control, and simplifies operation.

[0052] According to embodiments of this application, the vacuum degree during sintering is 0.1 Pa to 10 Pa, specifically within the ranges of 0.1 Pa, 0.5 Pa, 1 Pa, 2 Pa, 3 Pa, 4 Pa, 5 Pa, 6 Pa, 7 Pa, 8 Pa, 9 Pa, 10 Pa, or any two of these ranges. For example, the vacuum degree during sintering is 5 Pa. Therefore, a suitable vacuum degree can effectively reduce impurities and gases in the germanium telluride thermoelectric material preform, improving its purity and density. If the vacuum degree is too high, the gases inside the germanium telluride thermoelectric material preform may not be completely expelled, affecting the densification of its structure and reducing its thermoelectric performance; if the vacuum degree is too low, it may increase equipment operating costs and have limited effect on improving the thermoelectric performance of the porous germanium telluride thermoelectric material.

[0053] According to embodiments of this application, the sintering heating rate is 20℃ / min-100℃ / min, specifically 20℃ / min, 30℃ / min, 40℃ / min, 50℃ / min, 60℃ / min, 70℃ / min, 80℃ / min, 90℃ / min, 100℃ / min, or any range between two of these. As a specific example, the sintering heating rate is 70℃ / min. Therefore, an appropriate heating rate ensures uniform heating of the mixed powder during sintering, improving the uniformity and density of the porous germanium telluride thermoelectric material. Too low a heating rate will prolong the sintering time and reduce reaction efficiency; too high a heating rate may lead to excessive internal thermal stress in the germanium telluride thermoelectric material preform, causing cracking or structural inhomogeneity in the preform.

[0054] According to embodiments of this application, the sintering temperature is 400℃-650℃, specifically 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, or any range between two of these. As a specific example, the sintering temperature is 600℃. Thus, within the above temperature range, the raw materials can be fully sintered to form a dense structure, while also facilitating the decomposition of fluorides and the escape of gases. A sintering temperature that is too low may result in incomplete sintering of the mixed powder, leading to low density, poor thermoelectric performance, and hindering gas escape and the formation of a porous structure. A sintering temperature that is too high may cause the volatilization of low-melting-point elements, resulting in uneven composition of the germanium telluride thermoelectric material preform and reducing the thermoelectric performance of the porous germanium telluride thermoelectric material.

[0055] According to embodiments of this application, the sintering pressure is 20 MPa-60 MPa, specifically 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, or any range between two of these. As a specific example, the sintering pressure is 60 MPa. Therefore, an appropriate sintering pressure can promote the densification of the germanium telluride thermoelectric material preform, improving its strength and performance. If the sintering pressure is too low, the germanium telluride thermoelectric material may lack sufficient density, affecting its mechanical and thermoelectric properties. If the sintering pressure is too high, it may overburden the equipment and increase production costs.

[0056] According to embodiments of this application, the sintering time is 2-30 minutes, specifically 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or any range between two of these. As a specific example, the sintering time is 5 minutes. Therefore, an appropriate sintering time facilitates particle diffusion in the mixed powder, effectively controls grain size, and thus improves the density of the porous germanium telluride thermoelectric material. If the sintering time is too long, it may lead to excessive grain growth, reducing the strength of the porous germanium telluride thermoelectric material; if the sintering time is too short, most of the fluoride may not decompose, which is detrimental to the formation of a porous structure.

[0057] As a specific example, the mixed powder was subjected to discharge plasma sintering at a vacuum of 0.1 Pa to 10 Pa, a sintering pressure of 20 MPa to 60 MPa, and a sintering temperature of 400°C to 650°C for 2 to 30 minutes. After cooling, a germanium telluride thermoelectric material preform was obtained.

[0058] S30: Anneal the germanium telluride thermoelectric material preform to obtain porous germanium telluride thermoelectric material.

[0059] In this step, the germanium telluride thermoelectric material preform is annealed to promote uniform grain growth and adjustment, reduce grain boundary stress, and allow most of the gas remaining at the grain boundaries to escape, making the pore distribution more stable.

[0060] According to embodiments of this application, the annealing temperature is 400℃-550℃, specifically 400℃, 450℃, 500℃, 550℃, or any range between two of these. As a specific example, the annealing temperature is 450℃. This helps eliminate residual internal stress from sintering and reduces dislocation defects and microcracks. Excessively high annealing temperatures may cause significant volatilization of low-melting-point elements, leading to a decrease in carrier concentration and thus reducing thermoelectric performance; additionally, small pores in the porous structure may coalesce, reducing porosity and increasing lattice thermal conductivity. Conversely, excessively low annealing temperatures cannot effectively eliminate residual internal stress from sintering, easily leading to microcracks.

[0061] According to embodiments of this application, the annealing time is 6-8 hours, specifically 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, or any range between two of these. As a specific example, the annealing time is 8 hours. Therefore, an appropriate time helps eliminate sintering internal stress. If the annealing time is too short, the residual sintering internal stress may not be effectively eliminated, easily leading to microcracks; if the annealing time is too long, it may cause excessive grain growth, reduced grain boundaries, weakened phonon scattering, and increased lattice thermal conductivity.

[0062] As a specific example, the germanium telluride thermoelectric material preform is annealed at a temperature of 400℃-550℃ for 6h-8h to obtain porous germanium telluride thermoelectric material.

[0063] In a second aspect, this application provides a porous germanium telluride thermoelectric material prepared according to the method described above. The parameters and characteristics involved in this porous germanium telluride thermoelectric material are consistent with those in the preparation method described above, and will not be repeated here.

[0064] According to an embodiment of this application, the chemical composition of the porous germanium telluride thermoelectric material is Bi. x+z Ge 0.98-x- z TeCu y M z Wherein, M includes fluorides, 0.02≤x≤0.07, 0≤y≤0.03, 0≤z≤0.01, specifically, 0≤z≤0.01. Therefore, the porous germanium telluride thermoelectric material with the above composition exhibits good crystallinity and high structural density; simultaneously, it possesses a high power factor and low lattice thermal conductivity, thus resulting in a high thermoelectric figure of merit.

[0065] According to embodiments of this application, the composition of the fluoride is 0 < z ≤ 0.01, specifically such as 0.001, 0.005, 0.0025, 0.01, etc. Therefore, within the above range, after sintering the fluoride, many uniformly dispersed micropores can be formed. This allows for the scattering of phonons through the pore walls of the porous structure, thereby reducing lattice thermal conductivity and thermal conductivity, while maintaining a suitable porosity, thus optimizing the thermoelectric performance of the porous germanium telluride thermoelectric material. If z = 0, no gas may be generated, making it difficult to form a porous structure; if z > 0.01, excessive gas escape may lead to excessive interconnection of pores or excessively large pore sizes, damaging the structural integrity of the porous germanium telluride thermoelectric material.

[0066] According to embodiments of this application, the porosity of the porous germanium telluride thermoelectric material is 5%-25%. Therefore, a suitable porosity provides a sufficient number of phonon scattering centers, enhancing the phonon scattering effect, thereby reducing lattice thermal conductivity and overall thermal conductivity, and improving the thermoelectric figure of merit of the porous germanium telluride thermoelectric material; simultaneously, it maintains a certain level of mechanical strength. If the porosity is too low, the number of phonon scattering centers decreases, and the decrease in lattice thermal conductivity and overall thermal conductivity is limited; if the porosity is too high, it may disrupt lattice continuity, leading to a sharp drop in electrical conductivity and reducing the thermoelectric figure of merit.

[0067] The embodiments of this application are described in detail below.

[0068] Example 1

[0069] According to the chemical formula Bi 0.034 Ge 0.945 Te-Cu 0.02 -(BiF3) 0.001 15g of raw materials were weighed according to the stoichiometric ratio. The weighed masses of each raw material were as follows: Bi elemental powder (purity of 99.99%) 0.5357g, Ge elemental powder (purity of 99.99%) 5.0251g, Te elemental powder (purity of 99.999%) 9.3421g, Cu elemental powder (purity of 99.9%) 0.0930g, and BiF3 powder (purity of 99%) 0.0195g.

[0070] The weighed raw materials were placed into a tungsten carbide ball mill jar, and tungsten carbide balls with diameters of 10 mm, 6 mm, and 4 mm were added. The mass ratio of the grinding balls to the raw materials was 25:1 (the total mass of the added grinding balls was approximately 375 g). The ball mill jar was filled with an argon-hydrogen mixture as a protective gas (the hydrogen volume content was 5%, and the argon volume content was 95%). The mixture was ball-milled for 12 hours at a speed of 450 r / min in a planetary ball mill (QM-3SP2, Nanjing University Instrument Factory) to obtain a mixed powder.

[0071] The mixed powder was placed in a sintering mold, compacted, and then sintered in a spark plasma sintering furnace using spark plasma technology. The sintering temperature was 600℃ for 5 minutes under a vacuum of 5 Pa and a sintering pressure of 60 MPa. After cooling, a germanium telluride thermoelectric material preform was obtained.

[0072] After polishing the surface of the obtained germanium telluride thermoelectric material preform with sandpaper, it was annealed at 450℃ for 8 hours to obtain porous germanium telluride thermoelectric material.

[0073] Example 2

[0074] According to the chemical formula Bi 0.0325 Ge 0.945 Te-Cu 0.02-(BiF3) 0.0025 15g of raw materials were weighed according to the stoichiometric ratio. The weighed masses of each raw material were as follows: Bi elemental powder (purity of 99.99%) 0.4971g, Ge elemental powder (purity of 99.99%) 5.0230g, Te elemental powder (purity of 99.999%) 9.3382g, Cu elemental powder (purity of 99.9%) 0.0930g, and BiF3 powder (purity of 99%) 0.0487g.

[0075] The weighed raw materials were placed into a tungsten carbide ball mill jar, and tungsten carbide balls with diameters of 10 mm, 6 mm, and 4 mm were added. The mass ratio of the grinding balls to the raw materials was 25:1 (the total mass of the added grinding balls was approximately 375 g). The ball mill jar was filled with an argon-hydrogen mixture as a protective gas (the hydrogen volume content was 5%, and the argon volume content was 95%). The mixture was ball-milled for 12 hours at a speed of 450 r / min in a planetary ball mill (QM-3SP2, Nanjing University Instrument Factory) to obtain a mixed powder.

[0076] The mixed powder was placed in a sintering mold, compacted, and then sintered in a spark plasma sintering furnace using spark plasma technology. The sintering temperature was 600℃ for 5 minutes under a vacuum of 5 Pa and a sintering pressure of 60 MPa. After cooling, a germanium telluride thermoelectric material preform was obtained.

[0077] After polishing the surface of the obtained germanium telluride thermoelectric material preform with sandpaper, it was annealed at 450℃ for 8 hours to obtain porous germanium telluride thermoelectric material.

[0078] Example 3

[0079] According to the chemical formula Bi 0.03 Ge 0.945 Te-Cu 0.02 -(BiF3) 0.005 15g of raw materials were weighed according to the stoichiometric ratio. The weighed masses of each raw material were as follows: Bi elemental powder (purity of 99.99%) 0.4585g, Ge elemental powder (purity of 99.99%) 5.0196g, Te elemental powder (purity of 99.999%) 9.3317g, Cu elemental powder (purity of 99.9%) 0.0929g, and BiF3 elemental powder (purity of 99%) 0.0487g.

[0080] The weighed raw materials were placed into a tungsten carbide ball mill jar, and tungsten carbide balls with diameters of 10 mm, 6 mm, and 4 mm were added. The mass ratio of the grinding balls to the raw materials was 25:1 (the total mass of the added grinding balls was approximately 375 g). The ball mill jar was filled with an argon-hydrogen mixture as a protective gas (the hydrogen volume content was 5%, and the argon volume content was 95%). The mixture was ball-milled for 12 hours at a speed of 450 r / min in a planetary ball mill (QM-3SP2, Nanjing University Instrument Factory) to obtain a mixed powder.

[0081] The mixed powder was placed in a sintering mold, compacted, and then sintered in a spark plasma sintering furnace using spark plasma technology. The sintering temperature was 600℃ for 5 minutes under a vacuum of 5 Pa and a sintering pressure of 60 MPa. After cooling, a germanium telluride thermoelectric material preform was obtained.

[0082] After polishing the surface of the obtained germanium telluride thermoelectric material preform with sandpaper, it was annealed at 450℃ for 8 hours to obtain porous germanium telluride thermoelectric material.

[0083] Comparative Example 1

[0084] According to the chemical formula Bi 0.035 Ge 0.945 Te-Cu 0.02 15g of raw materials were weighed according to the stoichiometric ratio. The weighed masses of each raw material were 0.5357g of Bi elemental powder (purity of 99.99%), 5.0265g of Ge elemental powder (purity of 99.99%), 9.3447g of Te elemental powder (purity of 99.999%), and 0.0931g of Cu elemental powder (purity of 99.9%).

[0085] The weighed raw materials were placed into a tungsten carbide ball mill jar, and tungsten carbide balls with diameters of 10 mm, 6 mm, and 4 mm were added. The mass ratio of the grinding balls to the raw materials was 25:1 (the total mass of the added grinding balls was approximately 375 g). The ball mill jar was filled with an argon-hydrogen mixture as a protective gas (the hydrogen volume content was 5%, and the argon volume content was 95%). The mixture was ball-milled for 12 hours at a speed of 450 r / min in a planetary ball mill (QM-3SP2, Nanjing University Instrument Factory) to obtain a mixed powder.

[0086] The mixed powder was placed in a sintering mold, compacted, and then sintered in a spark plasma sintering furnace using spark plasma technology. The sintering temperature was 600℃ for 5 minutes under a vacuum of 5 Pa and a sintering pressure of 60 MPa. After cooling, a germanium telluride thermoelectric material preform was obtained.

[0087] After polishing the surface of the obtained germanium telluride thermoelectric material preform with sandpaper, it was annealed at 450℃ for 8 hours to obtain porous germanium telluride thermoelectric material.

[0088] Thermoelectric performance testing methods:

[0089] Electrical conductivity (σ): obtained by testing with a ZEM-3 manufactured by Quantum Design.

[0090] Seebeck coefficient (S): obtained by ZEM-3 test produced by Quantum Design.

[0091] Power factor (σS) 2 ): This is obtained by multiplying the conductivity (σ) and the Seebeck coefficient (S).

[0092] Thermal conductivity (κ): obtained by testing with LFA-457 manufactured by Netzsch GmbH, Germany.

[0093] Electronic thermal conductivity: calculated using the Weidmann-Frantz formula.

[0094] Lattice thermal conductivity (k L ): Obtained by subtracting electronic thermal conductivity from thermal conductivity.

[0095] Thermoelectric figure of merit (ZT): Derived from the formula ZT = σS 2 T / κ, where T is the absolute temperature, is calculated.

[0096] The test results are attached. Figure 4-10 The test results show that the electrical conductivity of the germanium telluride thermoelectric material prepared in Comparative Example 1 first decreases and then increases with increasing temperature, while the Seebeck coefficient first increases and then decreases with increasing temperature. The power factor first increases and then gradually levels off with increasing temperature. The total thermal conductivity first decreases and then increases with increasing temperature. The electronic thermal conductivity and lattice thermal conductivity first decrease and then increase with increasing temperature. The ZT value finally reaches 2.3 at 643 K.

[0097] The porous germanium telluride thermoelectric material prepared in Example 1 exhibits the following characteristics: electrical conductivity first decreases and then increases with increasing temperature; Seebeck coefficient first increases and then decreases with increasing temperature; power factor first increases and then gradually levels off with increasing temperature; total thermal conductivity first decreases and then increases with increasing temperature; electronic thermal conductivity and lattice thermal conductivity first decrease and then increase with increasing temperature; and the ZT value finally reaches 2.4 at 643 K, which is superior to that of Comparative Example 1.

[0098] The porous germanium telluride thermoelectric material prepared in Example 2 exhibits the following characteristics: electrical conductivity first decreases and then increases with increasing temperature; Seebeck coefficient first increases and then decreases with increasing temperature; power factor first increases and then gradually levels off with increasing temperature; total thermal conductivity first decreases and then increases with increasing temperature; electronic thermal conductivity and lattice thermal conductivity first decrease and then increase with increasing temperature; and the ZT value finally reaches 2.6 at 643 K, which is superior to that of Comparative Example 1.

[0099] The porous germanium telluride thermoelectric material prepared in Example 3 exhibits the following characteristics: electrical conductivity first decreases and then increases with increasing temperature; Seebeck coefficient first increases and then decreases with increasing temperature; power factor first increases and then gradually levels off with increasing temperature; total thermal conductivity first decreases and then increases with increasing temperature; electronic thermal conductivity and lattice thermal conductivity first decrease and then increase with increasing temperature; and the ZT value finally reaches 2.7 at 643 K, which is better than that of Comparative Example 1.

[0100] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0101] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing porous germanium telluride thermoelectric materials, characterized in that, include: The elemental powder raw material and the fluoride were ball-milled to obtain a mixed powder; The mixed powder is sintered to obtain a germanium telluride thermoelectric material preform; The germanium telluride thermoelectric material preform is annealed to obtain porous germanium telluride thermoelectric material.

2. The method according to claim 1, wherein the fluoride comprises at least one of bismuth trifluoride, cuprous fluoride, and silver hexafluoroantimonate, preferably bismuth trifluoride.

3. The method according to claim 1, characterized in that, The elemental powder raw material satisfies any one of the following: The elemental powder raw materials include Ge elemental powder and Te elemental powder; The elemental powder raw materials include Ge elemental powder, Te elemental powder and Bi elemental powder; The elemental powder raw materials include Ge elemental powder, Te elemental powder and Cu elemental powder; The elemental powder raw materials include Ge elemental powder, Te elemental powder, Bi elemental powder and Cu elemental powder.

4. The method according to claim 3, characterized in that, If any of the following conditions are met: The molar ratio of the Ge elemental powder to the Te elemental powder is 0.93-0.98:1; The molar ratio of the Ge elemental powder, Te elemental powder, and Bi elemental powder is 0.93-0.98:1:0.02-0.07; The molar ratio of the Ge elemental powder, Te elemental powder, and Cu elemental powder is 0.93-0.98:1:0-0.03; The molar ratio of the Ge elemental powder, Te elemental powder, Bi elemental powder and Cu elemental powder is 0.93-0.98:1:0.02-0.07:0-0.

03.

5. The method according to claim 1, characterized in that, The ball mill satisfies at least one of the following conditions: The ball-to-material ratio of the ball mill is 10-30:1; The rotational speed of the ball mill is 300 r / min-500 r / min; The ball milling time is 2h-12h.

6. The method according to claim 1, characterized in that, The sintering satisfies at least one of the following conditions: The vacuum degree of the sintering is 0.1 Pa-10 Pa; The sintering heating rate is 20℃ / min-100℃ / min; The sintering temperature is 400℃-650℃; The sintering pressure is 20MPa-60MPa; The sintering time is 2 min to 30 min.

7. The method according to claim 1, characterized in that, The annealing satisfies at least one of the following conditions: The annealing temperature is 400℃-550℃; The annealing time is 6-8 hours.

8. A porous germanium telluride thermoelectric material, characterized in that, Prepared according to the method described in claims 1-7.

9. The porous germanium telluride thermoelectric material according to claim 8, characterized in that, The chemical composition of the germanium telluride thermoelectric material is Bi. x+z Ge 0.98-x-z TeCu y M z ; Wherein, M includes fluoride, 0.02≤x≤0.07, 0≤y≤0.03, 0≤z≤0.01, preferably 0<z≤0.

01.

10. The porous germanium telluride thermoelectric material according to claim 8 or 9, characterized in that, The porosity of the porous germanium telluride thermoelectric material is 5%-25%.

Images