N-type gete-based thermoelectric material and preparation method thereof

Abstract

The application provides an n-type GeTe-based thermoelectric material and a preparation method thereof, and relates to the technical field of thermoelectric materials.The n-type GeTe-based thermoelectric material has a multilevel controllable microstructure, and a chemical formula is (GeTe) 1‑x (AgBiTe2) x , wherein x is 0-0.55.The n-type GeTe-based thermoelectric material is prepared by AgBiTe2 alloying, and the preparation steps include: mixing Ge powder, Bi powder, Te powder and Ag powder to obtain raw material particles, then vacuum sealing the raw material particles, and sequentially performing melting sintering, quenching, annealing, grinding and discharge plasma sintering.The n-type GeTe-based thermoelectric material and the preparation method thereof can realize multilevel controllable microstructure design, have excellent thermoelectric performance, fill the research gap of n-type GeTe materials, and have a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, and particularly relates to an n-type GeTe-based thermoelectric material and its preparation method. Background Technology

[0002] In recent years, with the rapid development of industrial society, energy crisis and environmental pollution have become the two most serious problems facing humanity today. Regarding resource waste, traditional heat engines still provide 80% of the electricity for humanity, but 70% of that is wasted as heat. If this waste heat could be effectively recovered, the energy crisis would be greatly alleviated. Therefore, developing a clean and efficient energy conversion technology is particularly important.

[0003] Thermoelectric conversion technology, as a green energy technology, enables the direct conversion of heat energy into electrical energy, effectively recovering waste heat without generating any pollution. The functional unit of thermoelectric technology is the thermoelectric module. High-performance thermoelectric modules require both high thermoelectric performance of p-type and n-type materials, as well as good compatibility between the two. Thermoelectric performance can be expressed by the dimensionless thermoelectric figure of merit (ZT), ZT = S 2 σT / κ, where S, σ, κ, and T represent the Seebeck coefficient, electrical conductivity, thermal conductivity (including electron conductivity), and κ, respectively. e and lattice κ l Thermal conductivity and absolute temperature. A high ZT value requires high electrical performance (determined by the power factor S). 2 σ represents low thermal properties (denoted by κ). Good compatibility requires matching coefficients of thermal expansion (CTE) between p-type and n-type materials.

[0004] With the development of materials design theory, high-performance thermoelectric materials such as low-temperature Bi₂Te₃, medium-temperature PbTe, SnTe, and GeTe, as well as high-temperature half-Heusler alloys, have been widely developed. Among them, lead-free GeTe-based materials exhibit exceptional thermoelectric performance. As a phase change material, GeTe undergoes a rhombohedral-to-cubic phase transition when the temperature rises to 700K. Furthermore, due to the presence of numerous Ge vacancies, the charge carriers in GeTe materials are predominantly holes, exhibiting strong p-type semiconductor characteristics. Through efforts in recent years, the ZT value of p-type GeTe materials has exceeded 2.5. Although p-type GeTe-based materials have achieved excellent thermoelectric performance, the practical application of GeTe-based materials remains a challenge due to the lack of highly compatible n-type counterparts. To improve the reliability of thermoelectric modules, n-type counterparts are usually chosen from materials with similar crystal structures and chemical compositions to p-type materials. Therefore, for GeTe-based thermoelectric modules, the optimal choice for n-type counterparts is n-type GeTe-based materials. It is worth noting that many patents for p-type GeTe materials have been published, but there are few reports on n-type GeTe, which seriously limits the practical application of GeTe-based materials.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide an n-type GeTe-based thermoelectric material and its preparation method to solve the above-mentioned problems.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides an n-type GeTe-based thermoelectric material, which has a multi-level controllable microstructure and its chemical formula is (GeTe). 1-x (AgBiTe2) x , where x is 0-0.55.

[0009] This invention also provides a method for preparing the aforementioned n-type GeTe-based thermoelectric material, which is obtained by alloying with AgBiTe2. The preparation steps include:

[0010] Ge powder, Bi powder, Te powder and Ag powder are mixed and refined to obtain raw material particles. The raw material particles are then vacuum sealed and sequentially subjected to melt sintering, quenching, annealing, grinding and spark plasma sintering to obtain the final product.

[0011] Optionally, the mixing and refining includes simultaneously placing the Ge powder, Bi powder, Te powder and Ag powder into a zirconia ball mill jar and mixing them evenly and refining the particles through pre-ball milling.

[0012] Optionally, the molar ratio of Ge powder, Bi powder, Te powder and Ag powder is (1-x):x:(1+x):x, where x is 0-0.55;

[0013] Preferably, the purity of the Ge powder, Bi powder, Te powder and Ag powder is not less than 99.9%;

[0014] More preferably, the purity of the Ge powder, Bi powder, Te powder and Ag powder reaches 99.99%.

[0015] Optionally, the vacuum sealing includes placing the raw material particles into a quartz tube and then evacuating the quartz tube using a vacuum pump;

[0016] Preferably, the vacuuming time is 10-30 minutes;

[0017] Preferably, the vacuuming time is 20 minutes;

[0018] Preferably, the vacuum level of the vacuum pump is less than or equal to 10. -3 Pa.

[0019] Optionally, before placing the raw material particles into the quartz tube, the quartz tube is further subjected to carbon plating.

[0020] The carbon plating process involves placing anhydrous ethanol into a quartz tube and heating it with an oxyhydrogen flame to form a carbon film on the inner wall of the quartz tube.

[0021] Optionally, the melt sintering includes heating the vacuum-sealed raw material particles to 850-1100°C in a muffle furnace at a heating rate of 1-10°C / min and holding at that temperature for 5-24 hours.

[0022] Preferably, the heating rate is 5°C / min;

[0023] Preferably, the target heating temperature is 950°C and the holding time is 12 hours.

[0024] Optionally, the quenching includes immersing the product that has undergone the melting and sintering process in ice water for quenching to obtain a quenched ingot;

[0025] The annealing is a high-temperature annealing performed on the quenched ingot in a muffle furnace;

[0026] The high temperature is 500-750℃, the gradient heating rate is 1-10℃ / min, and the isothermal time is 24-96h.

[0027] Preferably, the annealing temperature is 600°C and the holding time is 72 hours.

[0028] Preferably, the gradient heating rate is 5°C / min.

[0029] Optionally, the grinding is performed using an agate mortar and pestle for 20-60 minutes, followed by sieving through a 300-mesh sieve;

[0030] Preferably, the grinding time is 30 minutes or more.

[0031] Optionally, the process of spark plasma sintering includes placing the ground product in a graphite mold, using spark plasma sintering equipment to raise the system temperature to 400-650℃ at a rate of 30-100℃ / min, adjusting the pressure to 40-75MPa, and maintaining the constant temperature and pressure for 5-30 minutes.

[0032] Preferably, the process of spark plasma sintering is as follows: the grinding product is placed in a graphite mold, and the system is heated to 450°C at a rate of 50°C / min using spark plasma sintering equipment, the pressure is adjusted to 55MPa, and the temperature and pressure are maintained for 5 minutes.

[0033] The beneficial effects of this invention are:

[0034] Unlike existing p-type GeTe materials, this invention achieves the transformation from p-type semiconductor to n-type semiconductor, providing an n-type (GeTe) material with a multi-level controllable microstructure. 1-x (AgBiTe2) x This material fills a gap in n-type GeTe-based thermoelectric materials. The n-type GeTe-based thermoelectric material provided by this invention optimizes the electrical transport properties of the material, achieving approximately 6.2 μW / cm² at 423 K. -1 K -2 The power factor was achieved, breaking the existing record for n-type GeTe materials. Furthermore, multi-level precipitates were successfully introduced into the GeTe matrix through AgBiTe2 alloying, enhancing phonon scattering and achieving a power factor of approximately 3.4 W / m² at 423 K. -1 K -1 The material exhibits low lattice thermal conductivity. Through simultaneous optimization of electrical and thermal properties, the ZT value of the material provided by this invention reaches 0.5 at 423 K, enhancing the application potential of GeTe in thermoelectric power generation devices.

[0035] The method for preparing n-type GeTe-based thermoelectric materials provided by this invention reduces the band gap and increases the band degeneracy by controlling the alloying of AgBiTe2, while reducing the formation energy of Te vacancies. This enables the microstructure design of GeTe materials, concentrating nanodefects into the micron-sized precipitates. This increases phonon scattering while reducing the impact on charge carriers. The method is simple to operate, has a high success rate, and produces pure products, making it suitable for mass production and application. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 (GeTe) provided for this invention 1-x (AgBiTe2) x X-ray diffraction pattern of the material;

[0038] Figure 2 The (GeTe) prepared in Example 5 of this invention. 0.45 (AgBiTe2) 0.55 Transmission electron microscope images;

[0039] Figure 3 (GeTe) provided for this invention 1-x (AgBiTe2) x The Seebeck coefficient of the material varies with x;

[0040] Figure 4 (GeTe) provided for this invention 1-x (AgBiTe2) x Graph showing the relationship between the electrical conductivity of a material and x;

[0041] Figure 5 (GeTe) provided for this invention 1-x (AgBiTe2) x The power factor of the material varies with x.

[0042] Figure 6 (GeTe) provided for this invention 1-x (AgBiTe2) x The relationship between the lattice thermal conductivity of the material and x;

[0043] Figure 7 (GeTe) provided for this invention 1-x (AgBiTe2) x Graph showing the relationship between the overall thermal conductivity of a material and x;

[0044] Figure 8 (GeTe) provided for this invention 1-x (AgBiTe2) x The relationship between the ZT value of the material and x;

[0045] Figure 9X-ray diffraction patterns of the comparative materials provided in Comparative Examples 1-4;

[0046] Figure 10 The thermoelectric properties of the comparative materials provided for Comparative Examples 1-4 vary with temperature. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] First, the present invention will be explained in its entirety, as follows:

[0049] This invention provides an n-type GeTe-based thermoelectric material, which has a multi-level controllable microstructure and its chemical formula is (GeTe). 1-x (AgBiTe2) x , where x is 0-0.55.

[0050] Optionally, x can be any value between 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and 0.55.

[0051] This invention also provides a method for preparing the aforementioned n-type GeTe-based thermoelectric material, which is obtained by alloying with AgBiTe2. The preparation steps include:

[0052] Ge powder, Bi powder, Te powder and Ag powder with a purity of not less than 99.9% are mixed and refined to obtain raw material particles. The raw material particles are then vacuum sealed and sequentially subjected to melt sintering, quenching, annealing, grinding and spark plasma sintering to obtain the final product.

[0053] In an optional embodiment, the mixing and refining includes simultaneously placing the Ge powder, Bi powder, Te powder and Ag powder into a zirconia ball mill jar and mixing them uniformly and refining the particles through pre-ball milling.

[0054] In an optional embodiment, the molar ratio of Ge powder, Bi powder, Te powder and Ag powder is (1-x):x:(1+x):x, where x is 0-0.55;

[0055] Optionally, x can be any value between 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and 0.55;

[0056] In a preferred embodiment, the purity of the Ge powder, Bi powder, Te powder, and Ag powder is 99.99%.

[0057] The low-temperature rhombohedral phase of GeTe exhibits a wide bandgap and low band degeneracy. As the temperature increases, the low-temperature rhombohedral phase transforms into the high-temperature cubic phase. Consequently, the bandgap of GeTe decreases, and the band degeneracy increases, which is beneficial for carrier transitions from the valence band to the conduction band. Therefore, to realize n-type GeTe, it is necessary to extend the high-temperature cubic phase to the room temperature region to provide more and shorter carrier transport channels.

[0058] Because the intrinsic GeTe has a low Ge vacancy formation energy and a high Te vacancy formation energy, there are a large number of Ge vacancies in the matrix, resulting in hole carriers as the main charge carriers. The hole concentration is much greater than the electron concentration, exhibiting strong p-type semiconductor characteristics. Therefore, to achieve the pn transition, it is necessary to suppress Ge vacancy-induced Te vacancy formation through heavy doping and increase the electron carrier concentration.

[0059] At the same time, heavy doping inevitably introduces additional precipitates, causing carrier scattering and impairing electrical transport performance.

[0060] Therefore, to prepare high-performance n-type GeTe-based materials, it is necessary to consider both the preparation method and composition design of GeTe materials. In terms of composition design, this invention achieves the transformation from p-type GeTe to n-type GeTe through alloying with different contents of AgBiTe2. AgBiTe2 alloying can extend the high-temperature cubic phase to the low-temperature region, achieving a full-temperature-range cubic phase. Correspondingly, the band gap decreases, the band degeneracy increases, and more carrier transition channels are provided. Furthermore, by reducing the Te vacancy formation energy through AgBiTe2 alloying, the dominant carriers are converted from hole carriers to electron carriers, causing the Fermi level to shift from the valence band to the conduction band, thus realizing the transformation from p-type to n-type GeTe. Simultaneously, the introduction of a multi-level controllable microstructure optimizes electrical performance while reducing thermal performance, achieving simultaneous optimization of electrical / thermal properties.

[0061] In an optional embodiment, the vacuum sealing includes placing the raw material particles into a quartz tube and then evacuating the quartz tube using a vacuum pump.

[0062] In a preferred embodiment, the diameter of the quartz tube is 8 mm;

[0063] In a preferred embodiment, the vacuuming time is 10-30 minutes;

[0064] Optionally, the vacuuming time can be any value between 10 min, 15 min, 20 min, 25 min, and 30 min;

[0065] More preferably, the vacuuming time is 20 minutes;

[0066] More preferably, the vacuum level of the vacuum pumping is less than or equal to 10. -3 Pa.

[0067] In an optional embodiment, before placing the raw material particles into the quartz tube, the quartz tube is further subjected to a carbon plating treatment.

[0068] The carbon plating process involves placing anhydrous ethanol into a quartz tube and heating it with an oxyhydrogen flame to form a carbon film on the inner wall of the quartz tube.

[0069] In an optional embodiment, the melt sintering includes heating the vacuum-sealed raw material particles to 850-1100°C in a muffle furnace at a heating rate of 1-10°C / min and holding at that temperature for 5-24 hours.

[0070] Optionally, the melt sintering includes heating the vacuum-sealed raw material particles to any temperature between 850°C, 900°C, 950°C, 1000°C, 1050°C, and 1100°C in a muffle furnace at any heating rate between 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, and 10°C / min, and holding at that temperature for any value between 5h, 10h, 12h, 15h, 18h, 20h, and 24h.

[0071] In a preferred embodiment, the heating rate is 5°C / min;

[0072] In a preferred embodiment, the target heating temperature is 950°C, and the holding time is 12 hours.

[0073] In an optional embodiment, the quenching includes immersing the product that has undergone the melt sintering into ice water for quenching to obtain a quenched ingot.

[0074] The annealing is a high-temperature annealing performed on the quenched ingot in a muffle furnace;

[0075] The high temperature is 500-750℃, the gradient heating rate is 1-10℃ / min, and the isothermal time is 24-96h.

[0076] Optionally, the high temperature can be any value between 500℃, 550℃, 600℃, 650℃, 700℃ and 750℃, the gradient heating rate can be any value between 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min and 10℃ / min, and the isothermal time can be any value between 24h, 30h, 36h, 42h, 48h, 54h, 60h, 66h, 72h, 78h, 84h, 90h and 96h;

[0077] In a preferred embodiment, the annealing temperature is 600°C and the holding time is 72 hours.

[0078] In a preferred embodiment, the gradient heating rate is 5°C / min.

[0079] In an optional embodiment, the grinding is performed using an agate mortar and pestle for 20-60 minutes, followed by sieving through a 300-mesh sieve.

[0080] Optionally, the grinding time can be any value between 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min;

[0081] In a preferred embodiment, the grinding time is 30 minutes.

[0082] In an optional embodiment, the spark plasma sintering process includes placing the ground product in a graphite mold, using a spark plasma sintering device to raise the system temperature to 400-650°C at a rate of 30-100°C / min, adjusting the pressure to 40-75MPa, and maintaining the constant temperature and pressure for 5-30 minutes.

[0083] Optionally, the discharge plasma sintering equipment can raise the system temperature to any value between 400℃, 450℃, 500℃, 550℃, 600℃, and 650℃ at any rate between 30℃ / min, 40℃ / min, 50℃ / min, 60℃ / min, 70℃ / min, 80℃ / min, 90℃ / min, and 100℃ / min, and can adjust the pressure to any value between 40MPa, 45MPa, 50MPa, 55MPa, 60MPa, 65MPa, 70MPa, and 75MPa, and can maintain constant temperature and pressure for any value between 5min, 10min, 15min, 20min, 25min, and 30min;

[0084] In a preferred embodiment, the process of spark plasma sintering is as follows: the grinding product is placed in a graphite mold, and the system is heated to 450°C at a rate of 50°C / min using spark plasma sintering equipment, the pressure is adjusted to 55MPa, and the temperature and pressure are maintained at a constant level for 5 minutes.

[0085] This invention introduces a multi-level controllable microstructure into a GeTe matrix and adjusts parameters such as heating rate, sintering temperature, sintering time, and annealing temperature to modify the density and microstructure of the GeTe sample, ultimately obtaining (GeTe). 1-x (AgBiTe2) x The sample exhibits high density, diverse defect types, and numerous stress concentration regions. This effectively reduces carrier concentration and optimizes the material's electrical transport properties, achieving approximately 6.2 μW / cm² at 423 K. -1 K -2 The power factor was improved. Simultaneously, multi-level controllable microstructures, including Ag2Te micron-sized precipitates, grain boundaries, and Ag, were successfully introduced into the GeTe matrix through AgBiTe2 alloying. 1.33 Ge 0.17 Te nano-precipitates, planar defects, and point defects significantly reduce lattice thermal conductivity. Through simultaneous optimization of electrical and thermal properties, the ZT value of the material in this invention reaches 0.5 at 423 K.

[0086] It should be noted that the purity of the raw materials used in the embodiments of the present invention is 99.99%.

[0087] Example 1

[0088] The n-type GeTe-based thermoelectric material provided in this embodiment has the chemical formula (GeTe). 0.85 (AgBiTe2) 0.15 The sample was prepared using the method provided by this invention, and the specific steps are as follows:

[0089] Weighing and taking materials: Weigh Ge powder, Bi powder, Te powder and Ag powder respectively according to the molar ratio of 0.85:0.15:1.15:0.15;

[0090] Pre-ball milling: The weighed Ge powder, Bi powder, Te powder and Ag powder are simultaneously placed into a zirconia ball mill jar, mixed evenly and refined to obtain raw material particles for later use;

[0091] Carbon plating: A small amount of anhydrous ethanol is placed in a quartz tube and heated with an oxyhydrogen flame to carbonize it, forming a carbon film on the inner wall of the quartz tube.

[0092] Vacuum encapsulation: The raw material particles obtained by pre-ball milling are placed in a carbon-plated quartz tube and vacuumed for 20 minutes to prevent the raw material particles from contacting oxygen in the air and oxidizing during the reaction process;

[0093] Melting and sintering: The vacuum quartz tube sealed in the previous step is placed in a muffle furnace and slowly heated to 950°C at a rate of 5°C / min, and kept at the temperature for 12 hours to obtain a sintered ingot.

[0094] Quenching: Quickly place the sintered ingot in 0℃ ice water for quenching to obtain a quenched ingot;

[0095] Annealing: The quenched ingot obtained in the previous step is placed in a muffle furnace and slowly heated to 600°C at a rate of 5°C / min, and kept at the temperature for 72 hours. After cooling to room temperature, an annealed ingot is obtained.

[0096] Grinding: Take out the annealed ingot and place it in an agate mortar. Grind for 30 minutes, then pass it through a 300-mesh sieve to obtain a powder with uniform particles.

[0097] Spark plasma sintering (SPS): The ground powder is placed in a 12.7 mm graphite mold, and the powder is heated to 450 °C at 50 °C / min using a plasma spark sintering device. The temperature and pressure are maintained at 55 MPa for 5 min.

[0098] The material was then cooled to room temperature under vacuum, yielding an n-type GeTe-based thermoelectric material with the chemical formula (GeTe). 0.85 (AgBiTe2) 0.15 .

[0099] Example 2

[0100] The n-type GeTe-based thermoelectric material provided in this embodiment has the chemical formula (GeTe). 0.75 (AgBiTe2) 0.25 The sample was prepared using the method provided by this invention, and the specific steps are as follows:

[0101] Weighing and taking materials: Weigh Ge powder, Bi powder, Te powder and Ag powder respectively according to the molar ratio of 0.75:0.25:1.25:0.25;

[0102] Pre-ball milling: Same as in Example 1;

[0103] Carbon plating: Same as Example 1;

[0104] Vacuum sealing: Same as Example 1;

[0105] Melt sintering: Same as Example 1;

[0106] Quenching: Same as in Example 1;

[0107] Annealing: Same as in Example 1;

[0108] Grinding: Same as in Example 1;

[0109] SPS: Same as Example 1;

[0110] The material was then cooled to room temperature under vacuum, yielding an n-type GeTe-based thermoelectric material with the chemical formula (GeTe). 0.75 (AgBiTe2) 0.25 .

[0111] Example 3

[0112] The n-type GeTe-based thermoelectric material provided in this embodiment has the chemical formula (GeTe). 0.65 (AgBiTe2) 0.35 The sample was prepared using the method provided by this invention, and the specific steps are as follows:

[0113] Weighing and taking materials: Weigh Ge powder, Bi powder, Te powder and Ag powder respectively according to the molar ratio of 0.65:0.35:1.35:0.35;

[0114] Pre-ball milling: Same as in Example 1;

[0115] Carbon plating: Same as Example 1;

[0116] Vacuum sealing: Same as Example 1;

[0117] Melt sintering: Same as Example 1;

[0118] Quenching: Same as in Example 1;

[0119] Annealing: Same as in Example 1;

[0120] Grinding: Same as in Example 1;

[0121] SPS: Same as Example 1;

[0122] The material was then cooled to room temperature under vacuum, yielding an n-type GeTe-based thermoelectric material with the chemical formula (GeTe). 0.65 (AgBiTe2) 0.35 .

[0123] Example 4

[0124] The n-type GeTe-based thermoelectric material provided in this embodiment has the chemical formula (GeTe). 0.55 (AgBiTe2) 0.45 The sample was prepared using the method provided by this invention, and the specific steps are as follows:

[0125] Weighing and taking materials: Weigh Ge powder, Bi powder, Te powder and Ag powder respectively according to the molar ratio of 0.55:0.45:1.45:0.45;

[0126] Pre-ball milling: Same as in Example 1;

[0127] Carbon plating: Same as Example 1;

[0128] Vacuum sealing: Same as Example 1;

[0129] Melt sintering: Same as Example 1;

[0130] Quenching: Same as in Example 1;

[0131] Annealing: Same as in Example 1;

[0132] Grinding: Same as in Example 1;

[0133] SPS: Same as Example 1;

[0134] The material was then cooled to room temperature under vacuum, yielding an n-type GeTe-based thermoelectric material with the chemical formula (GeTe). 0.55 (AgBiTe2) 0.45 .

[0135] Example 5

[0136] The n-type GeTe-based thermoelectric material provided in this embodiment has the chemical formula (GeTe). 0.45 (AgBiTe2) 0.55 The sample was prepared using the method provided by this invention, and the specific steps are as follows:

[0137] Weighing and taking materials: Weigh Ge powder, Bi powder, Te powder and Ag powder respectively according to the molar ratio of 0.45:0.55:1.55:0.55;

[0138] Pre-ball milling: Same as in Example 1;

[0139] Carbon plating: Same as Example 1;

[0140] Vacuum sealing: Same as Example 1;

[0141] Melt sintering: Same as Example 1;

[0142] Quenching: Same as in Example 1;

[0143] Annealing: Same as in Example 1;

[0144] Grinding: Same as in Example 1;

[0145] SPS: Same as Example 1;

[0146] The material was then cooled to room temperature under vacuum, yielding an n-type GeTe-based thermoelectric material with the chemical formula (GeTe). 0.45 (AgBiTe2) 0.55 .

[0147] Comparative Example 1

[0148] The material provided in Comparative Example 1 has the chemical formula GeTe, and the specific preparation steps are as follows:

[0149] Weighing and taking materials: Weigh Ge powder and Te powder respectively according to a 1:1 molar ratio;

[0150] Pre-ball milling: The weighed Ge powder and Te powder are simultaneously placed into a zirconia ball mill jar, mixed evenly and refined to obtain raw material particles, which are then set aside.

[0151] Carbon plating: Same as Example 1;

[0152] Vacuum sealing: Same as Example 1;

[0153] Melt sintering: Same as Example 1;

[0154] Quenching: Same as in Example 1;

[0155] Annealing: Same as in Example 1;

[0156] Grinding: Same as in Example 1;

[0157] SPS: Same as Example 1;

[0158] The product was then cooled to room temperature under vacuum, and the chemical formula of the obtained product was GeTe.

[0159] Comparative Example 2

[0160] The chemical formula of the material provided in Comparative Example 2 is Ge. 0.88 Ag 0.12 Te, the specific preparation steps are as follows:

[0161] Weighing and taking materials: Weigh Ge powder, Ag powder, and Te powder respectively according to the molar ratio of 0.88:0.12:1;

[0162] Pre-ball milling: The weighed Ge powder, Ag powder, and Te powder are simultaneously placed into a zirconia ball mill jar, mixed evenly and refined to obtain raw material particles for later use;

[0163] Carbon plating: Same as Example 1;

[0164] Vacuum sealing: Same as Example 1;

[0165] Melt sintering: Same as Example 1;

[0166] Quenching: Same as in Example 1;

[0167] Annealing: Same as in Example 1;

[0168] Grinding: Same as in Example 1;

[0169] SPS: Same as Example 1;

[0170] The product was then cooled to room temperature under vacuum, yielding a product with the chemical formula Ge. 0.88 Ag 0.12 Te.

[0171] Comparative Example 3

[0172] The chemical formula of the material provided in Comparative Example 3 is Ge. 0.7 Bi 0.3 Te, the specific preparation steps are as follows:

[0173] Weighing and taking materials: Weigh Ge powder, Bi powder, and Te powder respectively according to a molar ratio of 0.7:0.3:1;

[0174] Pre-ball milling: The weighed Ge powder, Bi powder, and Te powder are simultaneously placed into a zirconia ball mill jar, mixed evenly and refined to obtain raw material particles for later use;

[0175] Carbon plating: Same as Example 1;

[0176] Vacuum sealing: Same as Example 1;

[0177] Melt sintering: Same as Example 1;

[0178] Quenching: Same as in Example 1;

[0179] Annealing: Same as in Example 1;

[0180] Grinding: Same as in Example 1;

[0181] SPS: Same as Example 1;

[0182] The product was then cooled to room temperature under vacuum, yielding a product with the chemical formula Ge. 0.7 Bi 0.3 Te.

[0183] Comparative Example 4

[0184] The chemical formula of the material provided in Comparative Example 4 is Ge. 0.58 Ag 0.12 Bi 0.3 Te was prepared using the method provided in this invention, and the specific steps are as follows:

[0185] Weighing and taking materials: Weigh Ge powder, Ag powder, Bi powder and Te powder respectively according to the molar ratio of 0.58:0.12:0.3:1;

[0186] Pre-ball milling: Same as in Example 1;

[0187] Carbon plating: Same as Example 1;

[0188] Vacuum sealing: Same as Example 1;

[0189] Melt sintering: Same as Example 1;

[0190] Quenching: Same as in Example 1;

[0191] Annealing: Same as in Example 1;

[0192] Grinding: Same as in Example 1;

[0193] SPS: Same as Example 1;

[0194] The product was then cooled to room temperature under vacuum, yielding a product with the chemical formula Ge. 0.58 Bi 0.3 Ag 0.12 Te.

[0195] The products obtained in Examples 1-5 and Comparative Examples 1-4 were subjected to structural characterization and performance testing, as detailed below:

[0196] Figure 1 (GeTe) provided for this invention 1-x (AgBiTe2) x X-ray diffraction pattern of the material. Figure 1 It can be seen that for (GeTe) 1-x (AgBiTe2) x For the material, when x is in the range of 0-0.2, the product has a rhombohedral structure. Furthermore, with increasing alloying degree, the (024) and (220) characteristic peaks between 40° and 45° merge into the (022) characteristic peak of the cubic phase. When x is 0.3, it exhibits the cubic phase characteristics of GeTe. The room-temperature cubic phase of GeTe has a low band gap and high band degeneracy, providing a channel for carrier transitions from the valence band to the conduction band. In addition, when x > 0.2, the sample contains Ag₂Te, Ag... 1.33 Ge 0.17 Te precipitates. Furthermore, with increasing AgBiTe2 content, the characteristic peak shifts regularly to the left due to the size effect.

[0197] Figure 2 The image shown is of (GeTe) prepared in Example 5 of this invention. 0.45 (AgBiTe2) 0.55 Transmission electron microscope (TEM) images. (By...) Figure 2 It can be seen that (GeTe) 0.45 (AgBiTe2) 0.55 There are micron-sized precipitates with nanophase aggregation and dense stress concentration regions. This nested defect type can effectively scatter phonons while minimizing carrier scattering.

[0198] Figure 3 The image shown is (GeTe). 1-x (AgBiTe2) xThe Seebeck coefficient of the material varies with the AgBiTe2 content, i.e., the change of x. (From...) Figure 3 It can be seen that when x is in the range of 0-0.3, the Seebeck coefficient of the product is positive, exhibiting p-type semiconductor characteristics; when x is between 0.35-0.55, (GeTe) 1-x (AgBiTe2) x The product exhibits a negative Seebeck coefficient, characteristic of an n-type semiconductor. For p-type samples, the Seebeck coefficient increases with increasing AgBiTe2 content due to the decrease in carrier concentration. For n-type samples, the Seebeck coefficient decreases with increasing AgBiTe2 content due to the decrease in effective mass.

[0199] Figure 4 The image shown is (GeTe). 1-x (AgBiTe2) x The graph shows the relationship between the material's electrical conductivity and the AgBiTe2 content, represented by the change in x. It can be observed that the conductivity exhibits a non-linear change with the AgBiTe2 content. With increasing AgBiTe2 content, the conductivity first decreases (p-type sample) and then increases (n-type sample). For the p-type sample, the conductivity decreases with increasing AgBiTe2 content due to the decrease in carrier concentration. For the n-type sample, the conductivity decreases with increasing AgBiTe2 content because the p-type Ag2Te precipitate provides additional hole carriers to neutralize electron carriers.

[0200] Figure 5 The image shown is (GeTe). 1-x (AgBiTe2) x The power factor of the material varies with the AgBiTe2 content, i.e., the change in x. (From...) Figure 5 It can be seen that, due to the synergistic optimization of conductivity and Seebeck, the power factor for n-type materials reaches 6.2 μW cm⁻¹ at x = 0.55 and 423 K. -1 K -2 The peak value.

[0201] Figure 6 The image shown is (GeTe). 1-x (AgBiTe2) x The relationship between the lattice thermal conductivity of the material and the AgBiTe2 content, i.e., the x-variance graph. (This is achieved through...) Figure 6 It can be seen that the lattice thermal conductivity of the material decreases with the increase of AgBiTe2 content due to the introduction of multi-scale defects such as nano-precipitates, point defects, micro-precipitates, and stress regions to enhance phonon scattering.

[0202] Figure 7 The image shown is (GeTe). 1-x (AgBiTe2) xThe graph shows the relationship between the overall thermal conductivity of the material and the AgBiTe2 content, i.e., the change in x. (This is achieved through...) Figure 7 It can be seen that, due to the decrease in lattice thermal conductivity, the thermal conductivity of the ingot decreases with the increase of AgBiTe2 content.

[0203] Figure 8 The image shown is (GeTe). 1-x (AgBiTe2) x The ZT value of the material varies with the AgBiTe2 content, i.e., the relationship between x and the ZT value. (This is achieved through...) Figure 8 It can be seen that, due to the synergistic optimization of electrothermal performance, a maximum ZT value of approximately 0.5 is obtained at 423K.

[0204] Figure 9 The images shown are X-ray diffraction patterns of the comparative materials provided in Comparative Examples 1-4. Figure 9 It can be seen that, in Comparative Example 2 (Ge 0.88 Ag 0.12 Te), Comparative Example 3 (Ge) 0.7 Bi 0.3 Te), Comparative Example 4 (Ge) 0.58 Ag 0.12 Bi 0.3 The materials provided by Te are all rhombohedral phases with a large number of precipitates. This means that these materials have large band gaps and low band degeneracy, which cannot provide a more efficient channel for carrier migration. Furthermore, the large number of precipitates will enhance carrier scattering and impair thermoelectric properties.

[0205] Figure 10 The graph shows the thermoelectric properties of the comparative materials provided in Comparative Examples 1-4 as a function of temperature. Figure 10 It can be seen that intrinsic GeTe (Comparative Example 1), Ge 0.88 Ag 0.12 Te (Comparative Example 2), Ge 0.7 Bi 0.3 Te (Comparative Example 3), Ge 0.58 Ag 0.12 Bi 0.3 The Seebeck coefficients of Te (Comparative Example 4) are all positive, indicating that these materials are all p-type semiconductors. This means that the transformation from p-type GeTe to n-type cannot be achieved by simply doping Bi, doping Ag, or doping a small amount of Ag on top of heavily doped Bi.

[0206] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing an n-type GeTe-based thermoelectric material, characterized in that, The thermoelectric material has a multi-level controllable microstructure and its chemical formula is (GeTe). 1-x (AgBiTe2) x Where x is 0.35-0.55; the multi-level controllable microstructure includes Ag2Te precipitates and Ag... 1.33 Ge 0.17 Te nano-precipitates; The thermoelectric material is prepared by alloying AgBiTe2, and the preparation steps include: Ge powder, Bi powder, Te powder and Ag powder are mixed and refined to obtain raw material particles. The raw material particles are then vacuum sealed and sequentially subjected to melt sintering, quenching, annealing, grinding and spark plasma sintering to obtain the final product. The molar ratio of Ge powder, Bi powder, Te powder and Ag powder is (1-x):x:(1+x):x, where x is 0.35-0.

55. The quenching process includes immersing the product that has undergone the melting and sintering process in ice water for quenching to obtain a quenched ingot. The annealing is a high-temperature annealing of the quenched ingot in a muffle furnace; the high temperature is 500-750℃, the gradient heating rate is 1-10℃ / min, and the isothermal time is 24-96 h.

2. The preparation method according to claim 1, characterized in that, The mixing and refining process involves simultaneously placing the Ge powder, Bi powder, Te powder, and Ag powder into a zirconia ball mill jar and mixing them uniformly and refining the particles through pre-ball milling.

3. The preparation method according to claim 1, characterized in that, The vacuum sealing process involves placing the raw material particles into a quartz tube and then evacuating the quartz tube using a vacuum pump. The vacuuming time is 10-30 minutes; The vacuum level of the vacuum pump is less than or equal to 10. -3 Pa.

4. The preparation method according to claim 3, characterized in that, Before the raw material particles are placed into the quartz tube, the quartz tube is first carbon-plated. The carbon plating process involves placing anhydrous ethanol into a quartz tube and heating it with an oxyhydrogen flame to form a carbon film on the inner wall of the quartz tube.

5. The preparation method according to claim 1, characterized in that, The melting and sintering process involves heating the vacuum-sealed raw material particles to 850-1100 °C in a muffle furnace at a heating rate of 1-10 °C / min and holding at that temperature for 5-24 h.

6. The preparation method according to claim 1, characterized in that, The grinding process includes grinding for 20-60 minutes using an agate mortar and pestle and then sieving.

7. The preparation method according to any one of claims 1-6, characterized in that, The process of spark plasma sintering includes placing the ground product in a graphite mold, using spark plasma sintering equipment to raise the system temperature to 400-650 ℃ at a rate of 30-100 ℃ / min, adjusting the pressure to 40-75 MPa, and maintaining the constant temperature and pressure for 5-30 min.

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