A high-performance p-type GeTe-based thermoelectric material and its preparation method

Abstract

This invention relates to a high-performance p-type GeTe-based thermoelectric material and its preparation method, belonging to the field of new energy materials. The invention aims to solve the problem of optimizing the performance of existing GeTe materials across the entire temperature range of 300K to 775K. The high-performance p-type GeTe-based thermoelectric material has the general chemical formula Ge. 0.84‑x‑y Pb 0.1 Sb 0.06 Cd x Te; Method: 1. Weighing; 2. Sealing; 3. Heating to melt and annealing; 4. Sintering. This invention is used for high-performance p-type GeTe-based thermoelectric materials and their preparation.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials. Background Technology

[0002] Thermoelectric materials enable the direct conversion between thermal and electrical energy, holding immense potential for solving energy problems. Based on operating temperature, thermoelectric materials can be categorized into low-temperature, medium-temperature, and high-temperature thermoelectric materials. Medium-temperature thermoelectric materials have significant applications in industrial waste heat recovery and automotive exhaust treatment, but their conversion efficiency limits their practical application. Achieving high conversion efficiency requires a high average ZT across the entire temperature range of 300K–775K. GeTe shows great potential in medium-temperature thermoelectric materials. As a phase change material, GeTe undergoes a phase transition around 700K, exhibiting a rhombohedral phase with space group R3m at low temperatures and a cubic phase with space group Fm-3m at high temperatures. The difference in crystal structure leads to differences in band structure: cubic GeTe is a direct bandgap semiconductor, while rhombohedral GeTe is an indirect bandgap semiconductor. Both phases possess multiple valence band apexes with similar energies, and the energy difference between the L and Σ valence band apexes in the cubic phase is lower than that in the rhombohedral phase. Due to the low Ge vacancy formation energy of intrinsic GeTe, the presence of a large number of vacancies results in a carrier concentration in intrinsic GeTe approaching 10. 21 cm -3 Much higher than 1 to 2 × 10 20 cm -3 The optimal carrier concentration is achieved, but this also deteriorates carrier mobility, resulting in an intrinsic GeTe thermoelectric figure of merit of only around 1. Further improvements in thermoelectric performance are needed for GeTe to be practically applied; current research has struggled to achieve performance optimization across the entire temperature range of 300K–775K. Summary of the Invention

[0003] This invention aims to address the problem that existing GeTe materials are difficult to optimize across the entire temperature range of 300K to 775K, and thus provides a high-performance p-type GeTe-based thermoelectric material and its preparation method.

[0004] A high-performance p-type GeTe-based thermoelectric material with the general chemical formula Ge 0.84-x-y Pb 0.1 Sb 0.06 Cd x Te, where 0 < x < 0.1, 0 ≤ y < 0.05.

[0005] A method for preparing a high-performance p-type GeTe-based thermoelectric material, comprising the following steps:

[0006] I. Weighing:

[0007] According to the general chemical formula Ge 0.84-x-y Pb 0.1Sb 0.06 Cd x The molar ratio of substances in Te is determined by weighing Ge blocks, Pb particles, Sb blocks, Cd particles, and Te blocks as raw materials, where 0 < x < 0.1 and 0 ≤ y < 0.05.

[0008] II. Sealing:

[0009] The raw material is placed in a quartz tube and vacuum sealed to obtain the sealed raw material;

[0010] III. Melting and Annealing Process:

[0011] The sealed raw material is placed in a muffle furnace and heated to melt at a temperature of 900℃~1000℃. Then it is cooled and annealed at a temperature of 550℃~650℃. Finally, it is cooled with the furnace to obtain an ingot.

[0012] IV. Sintering:

[0013] The method for preparing high-performance p-type GeTe-based thermoelectric materials involves grinding the ingot into powder, then placing it in a graphite mold for rapid hot pressing and sintering.

[0014] The beneficial effects of this invention are:

[0015] 1. The p-type GeTe-based thermoelectric material provided by this invention is prepared by air milling combined with rapid hot pressing sintering. The synthesized material has a uniform composition and no obvious second phase except for intrinsic Ge precipitation. At the same time, the preparation method is simple and convenient for large-scale industrial production.

[0016] 2. The p-type GeTe-based thermoelectric material provided by this invention significantly reduces thermal conductivity and carrier concentration by doping the Ge sites with 10% heavy element Pb, while optimizing carrier concentration by doping the Ge sites with 6% heterovalent donor element Sb. Cd doping achieves band convergence and improves the Seebeck coefficient. Introducing Ge vacancies further reduces thermal conductivity and promotes band convergence. Through the synergistic optimization of multiple methods, the room temperature carrier concentration is reduced to 1.00 × 10⁻⁶. 20 cm -3 ~3.60×10 20 cm -3 The thermal conductivity is 0.9 W / m² across the entire temperature range of 300 K to 775 K. -1 K -1 ~1.51Wm -1 K -1 The Seebeck coefficient is 110 μVK across the entire temperature range of 300 K to 775 K. -1 ~281μVK -1 The average ZT is 1.18 to 1.66 across the entire temperature range of 300K to 775K, and ultimately the highest ZT of the material is 1.9 to 2.3.

[0017] This invention relates to a high-performance p-type GeTe-based thermoelectric material and its preparation method. Attached Figure Description

[0018] Figure 1 The XRD pattern of the p-type GeTe-based thermoelectric material prepared in Example 1;

[0019] Figure 2 SEM image of the p-type GeTe-based thermoelectric material prepared in Example 1;

[0020] Figure 3 The graph shows the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 1 as a function of temperature.

[0021] Figure 4 The XRD pattern of the p-type GeTe-based thermoelectric material prepared in Example 2;

[0022] Figure 5 SEM image of the p-type GeTe-based thermoelectric material prepared in Example 2;

[0023] Figure 6 The graph shows the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 2 as a function of temperature.

[0024] Figure 7 The XRD pattern of the p-type GeTe-based thermoelectric material prepared in Example 3;

[0025] Figure 8 SEM image of the p-type GeTe-based thermoelectric material prepared in Example 3;

[0026] Figure 9 The graph shows the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 3 as a function of temperature. Detailed Implementation

[0027] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0028] Specific Implementation Method 1: This implementation method describes a high-performance p-type GeTe-based thermoelectric material with the general chemical formula Ge. 0.84-x-y Pb 0.1 Sb 0.06 Cd x Te, where 0 < x < 0.1, 0 ≤ y < 0.05.

[0029] The theoretical density of the p-type GeTe-based thermoelectric material in this specific embodiment is 6.18 g / cm³. 3 The density of the p-type GeTe-based thermoelectric material is preferably 6.2 g / cm³. 3 ~6.3g / cm3 .

[0030] The beneficial effects of this embodiment are:

[0031] 1. The p-type GeTe-based thermoelectric material provided by this invention is prepared by air milling combined with rapid hot pressing sintering. The synthesized material has a uniform composition and no obvious second phase except for intrinsic Ge precipitation. At the same time, the preparation method is simple and convenient for large-scale industrial production.

[0032] 2. The p-type GeTe-based thermoelectric material provided by this invention significantly reduces thermal conductivity and carrier concentration by doping the Ge sites with 10% heavy element Pb, while optimizing carrier concentration by doping the Ge sites with 6% heterovalent donor element Sb. Cd doping achieves band convergence and improves the Seebeck coefficient. Introducing Ge vacancies further reduces thermal conductivity and promotes band convergence. Through the synergistic optimization of multiple methods, the room temperature carrier concentration is reduced to 1.00 × 10⁻⁶. 20 cm -3 ~3.60×10 20 cm -3 The thermal conductivity is 0.9 W / m² across the entire temperature range of 300 K to 775 K. -1 K -1 ~1.51Wm -1 K -1 The Seebeck coefficient is 110 μVK across the entire temperature range of 300 K to 775 K. -1 ~281μVK -1 The average ZT is 1.18 to 1.66 across the entire temperature range of 300K to 775K, and ultimately the highest ZT of the material is 1.9 to 2.3.

[0033] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the highest thermoelectric figure of merit (ZT) of the high-performance p-type GeTe-based thermoelectric material is 1.9–2.3, and the average ZT is 1.18–1.66 across the entire temperature range of 300K–775K. Everything else is the same as in Specific Implementation Method One.

[0034] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the density of the high-performance p-type GeTe-based thermoelectric material is ≥6.20 g / cm³. 3 Everything else is the same as in specific implementation method one or two.

[0035] Specific Implementation Method Four: This implementation method provides a method for preparing a high-performance p-type GeTe-based thermoelectric material, which is carried out according to the following steps:

[0036] I. Weighing:

[0037] According to the general chemical formula Ge 0.84-x-y Pb 0.1 Sb0.06 Cd x The molar ratio of substances in Te is determined by weighing Ge blocks, Pb particles, Sb blocks, Cd particles, and Te blocks as raw materials, where 0 < x < 0.1 and 0 ≤ y < 0.05.

[0038] II. Sealing:

[0039] The raw material is placed in a quartz tube and vacuum sealed to obtain the sealed raw material;

[0040] III. Melting and Annealing Process:

[0041] The sealed raw material is placed in a muffle furnace and heated to melt at a temperature of 900℃~1000℃. Then it is cooled and annealed at a temperature of 550℃~650℃. Finally, it is cooled with the furnace to obtain an ingot.

[0042] IV. Sintering:

[0043] The method for preparing high-performance p-type GeTe-based thermoelectric materials involves grinding the ingot into powder, then placing it in a graphite mold for rapid hot pressing and sintering.

[0044] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the purity of the raw materials mentioned in step one is above 99.9%. Everything else is the same as in Specific Implementation Method Four.

[0045] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Four or Five in that the temperature is raised to 900℃ to 1000℃ within 10 to 14 hours in step three. Everything else is the same as in Specific Implementation Method Four or Five.

[0046] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods Four to Six in that: in step three, the temperature is lowered to 550℃ to 650℃ within 4 to 6 hours. Everything else is the same as in Specific Implementation Methods Four to Six.

[0047] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods Four to Seven in that: in step three, the annealing treatment is carried out at a temperature of 550℃ to 650℃ for 48 hours to 72 hours. Everything else is the same as in Specific Implementation Methods Four to Seven.

[0048] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Four to Eight in that the rapid hot-pressing sintering described in step four is specifically carried out according to the following steps: First, a vacuum is drawn to below 20 Pa; then, under a pressure of 55 MPa to 65 MPa, the temperature is raised to 500°C to 600°C; under a pressure of 55 MPa to 65 MPa and a temperature of 500°C to 600°C, the temperature is held for 30 to 45 minutes; finally, the temperature is air-cooled to room temperature without pressure. Everything else is the same as in Specific Implementation Methods Four to Eight.

[0049] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Four to Nine in that the temperature is increased from room temperature to 500℃ to 600℃ within 2 to 8 minutes. Everything else is the same as Specific Implementation Methods Four to Nine.

[0050] The beneficial effects of the present invention are verified using the following embodiments:

[0051] Example 1:

[0052] A method for preparing a high-performance p-type GeTe-based thermoelectric material, comprising the following steps:

[0053] I. Weighing:

[0054] According to the chemical formula Ge 0.83 Pb 0.1 Sb 0.06 Cd 0.01 The molar ratio of substances in Te is determined by weighing Ge blocks, Pb particles, Sb blocks, Cd particles and Te blocks as raw materials;

[0055] II. Sealing:

[0056] The raw material is placed in a quartz tube and vacuum sealed to obtain the sealed raw material;

[0057] III. Melting and Annealing Process:

[0058] The sealed raw material is placed in a muffle furnace and heated to 1000℃ for 12 hours. It is then heated and melted at 1000℃ for 10 hours, and then cooled to 600℃ within 4 hours (cooling rate of 100℃ / h). It is then annealed at 600℃ for 72 hours and finally cooled with the furnace to obtain the ingot.

[0059] IV. Sintering:

[0060] The ingot was ground into powder and then placed in a graphite mold with a diameter of 12.7 mm. The mold was first evacuated to a vacuum of less than 20 Pa, and then heated from room temperature to 550 °C for 5 min under a pressure of 60 MPa. The temperature was then maintained at 550 °C for 40 min under a pressure of 60 MPa. Finally, the mold was air-cooled to room temperature without pressure to obtain the p-type GeTe-based thermoelectric material.

[0061] The purity of the raw materials mentioned in step one is above 99.9%.

[0062] Figure 1 The image shows the XRD pattern of the p-type GeTe-based thermoelectric material prepared in Example 1; as can be seen from the image, the GeTe-based thermoelectric material is a single phase.

[0063] Figure 2The image shows a SEM image of the p-type GeTe-based thermoelectric material prepared in Example 1. As can be seen from the image, the GeTe-based thermoelectric material has no impurities except for intrinsic Ge precipitation, and the sample is uniform.

[0064] The density of the p-type GeTe-based thermoelectric material prepared in Example 1 is 6.23 g / cm³. 3 The room temperature conductivity is 1158.61 S / cm, and the carrier concentration is 1.66 × 10⁻⁶. 20 cm -3 The Seebeck coefficient is 128.41 μV / K, which is positive, indicating that it is a p-type organism. Its ZT value changes with temperature as follows: Figure 3 As shown ( Figure 3 The graph shows the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 1 as a function of temperature. At 675 K, the conductivity is 388.78 S / cm. -1 The Seebeck coefficient is 276.22 μVK. -1 The thermal conductivity is 0.96 W / m². -1 K -1 The ZT can reach 2.09; the average ZT is 1.42 in the entire temperature range of 300K to 775K, making it a high-performance thermoelectric material.

[0065] Example 2: This example differs from Example 1 in that: in step 1, the chemical formula Ge... 0.81 Pb 0.1 Sb 0.06 Cd 0.01 The raw materials for Te were weighed out as follows: Ge blocks, Pb particles, Sb blocks, Cd particles, and Te blocks. Everything else was the same as in Example 1.

[0066] Figure 4 The image shows the XRD pattern of the p-type GeTe-based thermoelectric material prepared in Example 2; as can be seen from the image, the GeTe-based thermoelectric material is a single phase.

[0067] Figure 5 The image shows a SEM image of the p-type GeTe-based thermoelectric material prepared in Example 2. As can be seen from the image, the GeTe-based thermoelectric material has no impurities except for intrinsic Ge precipitation, and the sample is uniform.

[0068] The density of the p-type GeTe-based thermoelectric material prepared in Example 2 is 6.25 g / cm³. 3 The room temperature conductivity is 1310.52 S / cm, and the carrier concentration is 1.81 × 10⁻⁶. 20 cm -3 The Seebeck coefficient is 128.30 μV / K, which is positive, indicating that it is a p-type organism. Its ZT value changes with temperature as follows: Figure 6 As shown ( Figure 6The graph shows the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 2 as a function of temperature. At 700 K, the conductivity is 405.86 S / cm. -1 The Seebeck coefficient is 280.45 μVK. -1 The thermal conductivity is 0.97 W / m². -1 K -1 The ZT can reach 2.28; the average ZT is 1.66 in the entire temperature range of 300K to 775K, making it a high-performance thermoelectric material.

[0069] Example 3: This example differs from Example 1 in that: in step 1, the chemical formula Ge is used... 0.79 Pb 0.1 Sb 0.06 Cd 0.01 The raw materials for Te were weighed out as follows: Ge blocks, Pb particles, Sb blocks, Cd particles, and Te blocks. Everything else was the same as in Example 1.

[0070] Figure 7 The image shows the XRD pattern of the p-type GeTe-based thermoelectric material prepared in Example 3; as can be seen from the image, the GeTe-based thermoelectric material is a single phase.

[0071] Figure 8 The image shows a SEM image of the p-type GeTe-based thermoelectric material prepared in Example 3. As can be seen from the image, the GeTe-based thermoelectric material has no impurities except for intrinsic Ge precipitation, and the sample is uniform.

[0072] The density of the p-type GeTe-based thermoelectric material prepared in Example 3 is 6.26 g / cm³. 3 The room temperature conductivity is 1393.72 S / cm, and the carrier concentration is 3.60 × 10⁻⁶. 20 cm -3 The Seebeck coefficient is 110.62 μV / K, which is positive, indicating that it is a p-type organism. Its ZT value changes with temperature as follows: Figure 9 As shown ( Figure 9 The graph shows the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 3 as a function of temperature. At 775 K, the conductivity is 690.68 S / cm. -1 The Seebeck coefficient is 220.65 μVK. -1 Thermal conductivity is 1.36 W / m² -1 K -1 The ZT can reach 1.91; the average ZT is 1.18 in the entire temperature range of 300K to 775K, making it a high-performance thermoelectric material.

Claims

1. A high-performance p-type GeTe-based thermoelectric material, characterized in that... Its general chemical formula is Ge 0.84-x- y Pb 0.1 Sb 0.06 Cd x Te, where x =0.01, 0≤ y The maximum thermoelectric figure of merit (ZT) of the high-performance p-type GeTe-based thermoelectric material is 1.9~2.3, and the average ZT is 1.18~1.66 over the entire temperature range of 300K~775K; the density of the high-performance p-type GeTe-based thermoelectric material is ≥6.20 g / cm³. 3 ; The above-mentioned high-performance p-type GeTe-based thermoelectric material is prepared according to the following steps: I. Weighing: According to the general chemical formula Ge 0.84-x-y Pb 0.1 Sb 0.06 Cd x The molar ratio of substances in Te was determined by weighing Ge blocks, Pb particles, Sb blocks, Cd particles, and Te blocks as raw materials, among which... x =0.01, 0≤ y ≤0.04; II. Sealing: The raw material is placed in a quartz tube and vacuum sealed to obtain the sealed raw material; III. Melting and Annealing Process: The sealed raw material is placed in a muffle furnace and heated to 900℃~1000℃ within 10h~14h. It is then heated and melted at 900℃~1000℃. The temperature is then lowered to 550℃~650℃ within 4h~6h, and annealed at 550℃~650℃ for 48h~72h. Finally, it is cooled with the furnace to obtain the ingot. IV. Sintering: The method for preparing high-performance p-type GeTe-based thermoelectric materials involves grinding the ingot into powder, then placing it in a graphite mold for rapid hot pressing and sintering. The rapid hot pressing sintering is carried out in the following steps: first, the vacuum is drawn to below 20 Pa, then the temperature is raised from room temperature to 500℃ to 550℃ within 2 min to 8 min under a pressure of 55MPa to 65MPa, and held at 500℃ to 550℃ for 30 min to 45 min under a pressure of 55MPa to 65MPa and a temperature of 500℃ to 550℃, and finally air-cooled to room temperature without pressure.

2. The high-performance p-type GeTe-based thermoelectric material according to claim 1, characterized in that... The purity of the raw materials mentioned in step one is above 99.9%.

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