A germanium telluride-based thermoelectric material, and a preparation method and application thereof

Abstract

The application discloses a germanium telluride-based thermoelectric material and application, and chemical formula is Ge 1‑n M n Te; wherein, M is selected from at least one of Bi, In, Cd; M mole fraction is n, 0 < n < 0.11. The application adopts the strategy of three-element common doping, and the common doping of three different elements not only optimizes the carrier concentration and energy band structure of germanium telluride, but also effectively reduces the lattice thermal conductivity of germanium telluride while maintaining high carrier mobility. Therefore, under the comprehensive regulation effect of electric and thermal performance, the thermoelectric figure of merit of germanium telluride is improved. The germanium telluride-based thermoelectric material of the application has simple, stable and efficient preparation process, excellent thermoelectric performance, and can well meet the demand of thermoelectric power generation application in the medium temperature zone.

Description

Technical Field

[0001] This application relates to a germanium telluride-based thermoelectric material, its preparation method, and its application, belonging to the field of thermoelectric material technology. Background Technology

[0002] Thermoelectric technology is the simplest technology to directly convert heat energy and electrical energy into each other. It can convert solar energy, geothermal energy, and waste heat from vehicles and industries into electricity, and conversely, it can also be used as a heat pump for cooling. Thermoelectric devices have advantages such as being all-solid-state, lightweight, compact, fast-responding, and having no moving parts or harmful working fluids. Their modular nature makes them easy to combine with other energy conversion technologies, a crucial characteristic for new energy applications, as no single technology can meet the world's energy needs. The thermoelectric properties of thermoelectric materials are mainly determined by the dimensionless figure of merit ZT = S. 2 σT / κ tot To measure, where S is the Seebeck coefficient, σ is the conductivity, and κ is the capacitance. tot Here, T represents the total thermal conductivity, and T represents the absolute temperature. These thermoelectric transport parameters are coupled and influence each other, making it challenging to improve thermoelectric performance.

[0003] Germanium telluride, a thermoelectric material in the mid-temperature range, possesses a crystal structure and electronic band structure similar to lead telluride, but does not contain the toxic element lead, thus showing promise as an effective substitute for lead telluride. Traditional methods for optimizing the thermoelectric performance of germanium telluride systems involve using doping to generate nanoscale second phases and micro-structures in the matrix, reducing the lattice thermal conductivity—the only uncoupled variable—and improving thermal transport properties, thereby enhancing the material's thermoelectric performance. In recent years, band engineering has also been widely applied to optimize the electrical transport properties of germanium telluride materials, targeting its band defects. While commonly used defect design and band manipulation can optimize the effective carrier mass and lattice thermal conductivity, they also reduce carrier mobility, limiting the improvement in the average thermoelectric figure of merit of germanium telluride thermoelectric materials. Summary of the Invention

[0004] Maintaining high carrier mobility is key to improving the average thermoelectric figure of merit of materials over a wide temperature range.

[0005] According to one aspect of this application, a germanium telluride-based thermoelectric material is provided. By employing a strategy of co-doping with Bi, In, and Cd elements, the scattering of charge carriers and phonons can be effectively balanced, and the relationship between charge carrier mobility, effective mass, and charge carrier concentration can be synergistically controlled, thereby significantly improving the thermoelectric figure of merit of germanium telluride over a wide temperature range.

[0006] According to one aspect of this application, a germanium telluride-based thermoelectric material is provided, wherein the chemical formula of the germanium telluride-based thermoelectric material is Ge. 1-n M n Te.

[0007] M is selected from at least one of Bi, In, and Cd.

[0008] The mole fraction of M is n, where 0 < n ≤ 0.11.

[0009] Furthermore, the chemical formula of the germanium telluride-based thermoelectric material is Ge. 1-x-y-z Bi x In y Cd z Te;

[0010] Where x represents the mole fraction of the dopant element Bi, and its value ranges from 0 to x to 0.06; the value range of x is independently selected from any value among 0, 0.02, 0.04, and 0.06 or any range between two of them.

[0011] y represents the mole fraction of the dopant element In, and its value range is 0 ≤ y ≤ 0.01; optionally, the value range of y is independently selected from any value among 0, 0.002, 0.004, 0.006, 0.008, 0.01 or any range between two of them.

[0012] z represents the mole fraction of the dopant element Cd, and its value range is 0 ≤ z ≤ 0.04; optionally, the value range of z can be independently selected from any value of 0, 0.01, 0.02, 0.03, 0.04 or any value between any two.

[0013] According to another aspect of this application, a method for preparing the above-mentioned germanium telluride-based thermoelectric material is provided, comprising the following steps:

[0014] The raw materials containing elemental Ge, elemental M, and elemental Te are mixed, calcined, and annealed to obtain the germanium telluride-based thermoelectric material.

[0015] The roasting temperature is 900–950°C;

[0016] Optionally, the roasting temperature is any value among 900℃, 910℃, 920℃, 930℃, 940℃, and 950℃, or a range between any two.

[0017] The roasting time is 1 to 3 hours.

[0018] Optionally, the roasting time is any value among 1h, 2h, and 3h, or a range between any two.

[0019] The calcination is carried out in a vacuum environment;

[0020] The vacuum level of the vacuum environment is 5 Pa to 10 Pa.

[0021] Optionally, the vacuum degree of the vacuum environment is any value among 5Pa, 6Pa, 7Pa, 8Pa, 9Pa, and 10Pa, or a range between any two.

[0022] The annealing temperature is 600–650°C;

[0023] Optionally, the annealing temperature is any value among 600℃, 610℃, 620℃, 630℃, 640℃, and 650℃, or a range between any two.

[0024] The annealing time is 48–72 hours.

[0025] Optionally, the annealing time is any value among 48h, 56h, 64h, and 72h, or a range between any two.

[0026] Furthermore, when M includes Bi, In, and Cd:

[0027] Includes the following steps:

[0028] Raw materials containing Ge, Bi, In, Cd, and Te sources are placed under vacuum conditions and then melted, quenched, annealed, cooled, and ball-milled to obtain powder.

[0029] The germanium telluride-based thermoelectric material can be obtained by sintering the powder at high temperature.

[0030] The amounts of Ge source, Bi source, In source, Cd source and Te source added satisfy the molar ratio of each element in Formula I.

[0031] Optionally, the Ge source in the raw material is selected from elemental Ge; the Bi source is selected from elemental Bi; the In source is selected from elemental In; the Cd source is selected from Cd; the Te source is selected from elemental Te; and the N source is selected from elemental N.

[0032] Optionally, the melting conditions are: melting temperature 900-950℃; melting time 1-3h.

[0033] Optionally, the quenching medium is ice water or liquid nitrogen.

[0034] Optionally, the annealing conditions are: annealing temperature 600-650℃; annealing time 48-72h.

[0035] Optionally, the upper limit of the high-temperature sintering temperature is independently selected from 560℃, 500℃, 450℃, and 400℃, and the lower limit is independently selected from 360℃, 500℃, 450℃, and 400℃.

[0036] Optionally, the conditions for high-temperature sintering are: sintering temperature 500-600℃, sintering pressure 50-60 MPa, and sintering time 5-15 min.

[0037] As one specific implementation method, the germanium telluride-based thermoelectric material adopts the following steps:

[0038] Step 1: Prepare the material by weighing the chemical components according to Formula I and placing them into a clean quartz glass tube; seal it under a vacuum of <1 Pa.

[0039] Step 2: Melt and shake, melt at 950℃ for 0.5 hours, shake for 0.5 hours.

[0040] Step 3: Quenching. The high-temperature molten material obtained in Step 2 is quickly placed in ice water until it is completely solidified into an ingot.

[0041] Step 4: Annealing. Place the ingot obtained in Step 3 into an annealing furnace and anneal at 600℃ for 48 hours.

[0042] Step 5: Ingot crushing. In a glove box, crush the ingot obtained in step 4 using an agate mortar and pestle for 10-30 minutes under inert gas protection.

[0043] Step 6: Hot pressing and sintering. The powder obtained in step 5 is placed into a metal / graphite mold, and the temperature and pressure are uniformly increased to 60MPa and held at 550℃ for 10 minutes. Finally, after cooling to room temperature, the pressure is uniformly released to obtain the sample.

[0044] Specifically, when the germanium telluride-based thermoelectric material prepared in this application is used for electrothermal transport performance testing, the thermoelectric material is cut into samples of 3mm×3mm×13mm and 1.5mm×10mm×10mm.

[0045] According to another aspect of this application, an application is provided for the germanium telluride-based thermoelectric material described above or prepared by the above method, used in a mid-temperature thermoelectric converter.

[0046] The operating temperature of the medium-temperature thermoelectric converter is 177–500°C.

[0047] The beneficial effects that this application can produce include:

[0048] This application employs a strategy of co-doping with three different elements. This co-doping not only optimizes the carrier concentration and band structure of germanium telluride but also effectively reduces its lattice thermal conductivity while maintaining high carrier mobility. Therefore, the thermoelectric figure of merit of germanium telluride is improved through comprehensive regulation of its electrical and thermal properties. The germanium telluride-based thermoelectric material of this application has a simple, stable, and efficient preparation process and excellent thermoelectric performance, which can well meet the needs of mid-temperature thermoelectric power generation applications.

[0049] Specifically:

[0050] 1) The germanium telluride-based thermoelectric material for power generation in the low and medium temperature range provided in this application significantly improves the density of states and effective mass, thereby effectively improving the overall electrical performance of the material.

[0051] 2) The germanium telluride-based thermoelectric material for power generation in the low and medium temperature range provided in this application maintains a high carrier mobility and effectively preserves the overall electrical performance of the material.

[0052] 3) The germanium telluride-based thermoelectric material for power generation in the low-to-medium temperature range provided in this application effectively enhances the selective scattering of phonons, thereby reducing the lattice thermal conductivity of the germanium telluride-based thermoelectric material.

[0053] 4) The germanium telluride-based thermoelectric material for power generation in the low and medium temperature range provided in this application significantly improves the thermoelectric figure of merit ZT of the germanium telluride-based thermoelectric material in a wide temperature range and improves the thermoelectric conversion efficiency of the germanium telluride-based thermoelectric material in the low and medium temperature environment.

[0054] 5) The method for preparing germanium telluride-based thermoelectric materials provided in this application has the advantages of short preparation cycle and simple process.

[0055] 6) The method for preparing dense bulk thermoelectric materials provided in this application can avoid sample cracking and breakage. Attached Figure Description

[0056] Figure 1 The graphs show the relationship between conductivity and temperature for Examples 1-3 and Comparative Example 1.

[0057] Figure 2 The graphs show the Seebeck coefficient versus temperature for Examples 1-3 and Comparative Example 1.

[0058] Figure 3 The graphs show the power factor versus temperature for Examples 1-3 and Comparative Example 1.

[0059] Figure 4 The graphs show the relationship between thermal conductivity and temperature for Examples 1-3 and Comparative Example 1.

[0060] Figure 5 The graphs show the relationship between lattice thermal conductivity and temperature for Examples 1-3 and Comparative Example 1.

[0061] Figure 6 The thermoelectric figure of merit of Examples 1-3 and Comparative Example 1 are graphs showing the relationship between temperature and the thermoelectric figure of merit. Detailed Implementation

[0062] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0063] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0064] Comparative Example 1

[0065] This comparative example is a comparison of Examples 1, 2, and 3 below. This comparative example is a germanium telluride-based bulk thermoelectric material without Bi, In, and Cd doping. Specifically:

[0066] (1) Weigh 15g of raw material, weigh germanium granules (99.999%) and tellurium granules (99.999%) according to the chemical formula GeTe, put the raw material into a clean quartz tube and fix it on the sealing device, and seal the quartz tube under the condition that the vacuum negative pressure is not higher than 0.8Pa; place the sealed quartz tube in a swing furnace at a temperature of 950℃, keep it at the temperature for half an hour and then turn on the swing switch to make the two better combine; after swinging for half an hour, take out the quartz tube containing the high temperature molten material, and then immediately insert it into ice water for quenching; place the quenched ingot in an annealing furnace and anneal it at 600℃ for two days; manually grind the obtained ingot into powder for 10 minutes.

[0067] (2) The prepared powder was poured into a graphite mold, and the top and bottom were sealed with graphite carbon paper and graphite carbon rods. Then, it was placed in a vacuum hot press furnace for vacuum sintering. The sintering temperature was 550℃, the pressure was 60MPa, and the holding time was 10min. After the holding time was completed, the heating power was turned off, and the pressure was released when the temperature dropped to 40℃. After cooling to room temperature, the vacuum was broken, the sample was taken out, and the cylindrical bulk thermoelectric material of germanium telluride was obtained.

[0068] (3) Cut the sintered cylindrical block thermoelectric material into strips of 2.5mm×2.5mm×12mm and thin slices of 1.5mm×10mm×10mm, respectively, to measure the electrical transport properties and thermal transport properties.

[0069] Example 1

[0070] (1) Weigh 15g of the raw material according to the chemical formula Ge 0.94 Bi 0.06 Te weighed germanium granules (99.999%), bismuth granules (99.999%), and tellurium granules (99.999%), loaded the raw materials into a clean quartz tube, and fixed it on a sealing device. The quartz tube was sealed while ensuring that the vacuum negative pressure did not exceed 0.8 Pa. The sealed quartz tube was placed in a swing furnace at 950℃ and kept at that temperature for half an hour. Then the swing switch was turned on to facilitate better bonding between the two. After swinging for half an hour, the quartz tube containing the high-temperature molten material was removed and immediately immersed in ice water for quenching. The ingot obtained after quenching was placed in an annealing furnace and annealed at 600℃ for two days. The resulting ingot was manually ground into powder for 10 minutes.

[0071] (2) The prepared powder was poured into a graphite mold, and the top and bottom were sealed with graphite carbon paper and graphite carbon rods. Then, it was placed in a vacuum hot press furnace for vacuum sintering. The sintering temperature was 550℃, the pressure was 60MPa, and the holding time was 10min. After the holding time was completed, the heating power was turned off, and the pressure was released when the temperature dropped to 40℃. After cooling to room temperature, the vacuum was broken, the sample was taken out, and the cylindrical bulk thermoelectric material of germanium telluride was obtained.

[0072] (3) Cut the sintered cylindrical block thermoelectric material into strips of 2.5mm×2.5mm×12mm and thin slices of 1.5mm×10mm×10mm, respectively, to measure the electrical transport properties and thermal transport properties.

[0073] Example 2

[0074] (1) Weigh 15g of the raw material according to the chemical formula Ge 0.94 Bi 0.06 In 0.01 Te weighed germanium granules (99.999%), bismuth granules (99.999%), indium granules (99.999%), and tellurium granules (99.999%). The raw materials were loaded into a clean quartz tube and fixed to a sealing device. The quartz tube was sealed while maintaining a vacuum pressure not exceeding 0.8 Pa. The sealed quartz tube was placed in a swaying furnace at 950℃ and held for half an hour. The swaying switch was then turned on to facilitate better bonding between the two materials. After swaying for half an hour, the quartz tube containing the high-temperature molten material was removed and immediately quenched in ice water. The resulting ingot was placed in an annealing furnace and annealed at 600℃ for two days. The resulting ingot was manually ground into powder for 10 minutes.

[0075] (2) The prepared powder was poured into a graphite mold, and the top and bottom were sealed with graphite carbon paper and graphite carbon rods. Then, it was placed in a vacuum hot press furnace for vacuum sintering. The sintering temperature was 550℃, the pressure was 60MPa, and the holding time was 10min. After the holding time was completed, the heating power was turned off, and the pressure was released when the temperature dropped to 40℃. After cooling to room temperature, the vacuum was broken, the sample was taken out, and the cylindrical bulk thermoelectric material of germanium telluride was obtained.

[0076] (3) Cut the sintered cylindrical block thermoelectric material into strips of 2.5mm×2.5mm×12mm and thin slices of 1.5mm×10mm×10mm, respectively, to measure the electrical transport properties and thermal transport properties.

[0077] Example 3

[0078] (1) Weigh 15g of the raw material according to the chemical formula Ge 0.94 Bi 0.06 In 0.01 Cd 0.04Te weighed germanium granules (99.999%), bismuth granules (99.999%), indium granules (99.999%), cadmium granules (99.999%), and tellurium granules (99.999%). The raw materials were loaded into a clean quartz tube and fixed to a sealing device. The quartz tube was sealed while maintaining a vacuum pressure not exceeding 0.8 Pa. The sealed quartz tube was placed in a swing furnace at 950℃ and held for half an hour. The swing switch was then turned on to facilitate better bonding between the two materials. After swinging for half an hour, the quartz tube containing the high-temperature molten material was removed and immediately quenched in ice water. The resulting ingot was placed in an annealing furnace and annealed at 600℃ for two days. The resulting ingot was manually ground into powder for 10 minutes.

[0079] (2) The prepared powder was poured into a graphite mold, and the top and bottom were sealed with graphite carbon paper and graphite carbon rods. Then, it was placed in a vacuum hot press furnace for vacuum sintering. The sintering temperature was 550℃, the pressure was 60MPa, and the holding time was 10min. After the holding time was completed, the heating power was turned off, and the pressure was released when the temperature dropped to 40℃. After cooling to room temperature, the vacuum was broken, the sample was taken out, and the cylindrical bulk thermoelectric material of germanium telluride was obtained.

[0080] (3) Cut the sintered cylindrical block thermoelectric material into strips of 2.5mm×2.5mm×12mm and thin slices of 1.5mm×10mm×10mm, respectively, to measure the electrical transport properties and thermal transport properties.

[0081] Test Example 1

[0082] Thermoelectric performance testing

[0083] Figure 1 The graphs show the relationship between the electrical conductivity and temperature of the thermoelectric materials prepared in Examples 1-3 and the GeTe-based thermoelectric material in Comparative Example 1. It can be observed that the electrical conductivity of the GeTe matrix remains high throughout the entire temperature range: 7302 S·cm at room temperature. 1 As the doping concentration increased, the conductivity at room temperature in Example 1 was 2298 S·cm. 1 The conductivity at room temperature in Example 2 was 1511 S·cm. 1 The conductivity at room temperature in Example 3 was 836 S·cm. 1 The decrease in conductivity is mainly due to the decrease in carrier concentration.

[0084] Figure 2The graphs show the Seebeck coefficient versus temperature for the thermoelectric materials prepared in Examples 1-3 and the GeTe-based thermoelectric material of Comparative Example 1. Compared to Comparative Example 1, the Seebeck coefficient of Examples 1-3 is significantly improved across the entire temperature range with increasing doping concentration. The improvement in Seebeck coefficient is mainly due to two factors: 1) a decrease in carrier concentration; and 2) an improvement in the effective mass of the density of states resulting from the optimization of the band structure by In and Cd doping.

[0085] Figure 3 The graphs show the power factor versus temperature of the thermoelectric materials prepared in Examples 1-3 and the GeTe-based thermoelectric material of Comparative Example 1. It can be observed that, compared to Comparative Example 1, the power factor of the samples in Examples 1-3 increases significantly in the low-to-medium temperature range. This phenomenon is beneficial for improving thermoelectric performance in the low-to-medium temperature range, thereby better meeting the application requirements for high-efficiency power generation in this region.

[0086] Figure 4 , 5 The graphs show the relationship between the total thermal conductivity and lattice thermal conductivity of the thermoelectric materials prepared in Examples 1-3 and the GeTe-based thermoelectric material of Comparative Example 1, as well as temperature. Compared to Comparative Example 1, the total thermal conductivity and lattice thermal conductivity of the samples in Examples 1-3 decreased significantly throughout the entire temperature range. The decrease in thermal conductivity is mainly due to the effective enhancement of selective phonon scattering by the doping of Bi, In, and Cd elements.

[0087] Figure 6 The graphs show the relationship between the thermoelectric figure of merit (TFP) and temperature for the thermoelectric materials prepared in Examples 1-3 and the GeTe-based thermoelectric material of Comparative Example 1. Due to the increase in power factor and the decrease in thermal conductivity, the TFP of Examples 1-3 increases significantly; for Example 3, compared to Comparative Example 1, the peak TFP value increases from 0.99 to 2.12. Simultaneously, the average TFP value (300-773 K) of the material is greatly improved, enhancing the thermoelectric efficiency of the material in low-to-medium temperature environments, enabling the material to be efficiently used in low-to-medium temperature power generation modules.

[0088] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A germanium telluride-based thermoelectric material, characterized in that, The chemical formula of the germanium telluride-based thermoelectric material is Ge. 1-x-y- z Bi x In y Cd z Te; Where x represents the mole fraction of the dopant element Bi, and its value ranges from 0.

02. x 0.06; y represents the mole fraction of the dopant element In, and its value ranges from 0.

002. y 0.01; z represents the mole fraction of the dopant element Cd, and its value ranges from 0.

01. z 0.

04.

2. A method for preparing the germanium telluride-based thermoelectric material according to claim 1, characterized in that, Includes the following steps: Raw materials containing germanium, bismuth, indium, cadmium, and tellurium particles are mixed and calcined under vacuum at a temperature of 900-950℃ for 1-3 hours and a vacuum degree of 5-10 Pa. The mixture is then annealed at 600-650℃ for 48-72 hours to obtain the germanium telluride-based thermoelectric material.

3. The preparation method according to claim 2, characterized in that, The roasting temperature is 920~950℃; The roasting time is 1-2 hours.

4. The preparation method according to claim 2, characterized in that, The annealing temperature is 600~630℃; The annealing time is 48~64 hours.

5. The application of the germanium telluride-based thermoelectric material according to claim 1 or the germanium telluride-based thermoelectric material prepared by the preparation method according to any one of claims 2 to 4, characterized in that, Used in medium-temperature thermoelectric converters.

6. The application according to claim 5, characterized in that, The operating temperature of the medium-temperature thermoelectric converter is 177~500℃.

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