High-performance p-type GeTe-based thermoelectric material and preparation method thereof

Abstract

The invention discloses a high-performance p-type GeTe-based thermoelectric material and a preparation method thereof, and belongs to the field of new energy materials. The invention aims to solve the problem that the performance optimization of the existing GeTe in the full temperature range of 300K-775K is difficult to realize. The chemical general formula of the high-performance p-type GeTe-based thermoelectric material is Ge < 0.84-x-y > Pb < 0.1 > Sb < 0.06 > Cd < x > Te, the method comprises the following steps: 1, weighing; 2, sealing; 3, heating, melting and annealing treatment; and 4, sintering. The invention is used for the high-performance p-type GeTe-based thermoelectric material and the preparation thereof.

Description

Technical Field

[0001] The invention belongs to the field of new energy materials. Background Art

[0002] Thermoelectric materials can realize the direct conversion of thermal energy and electrical energy, and have great potential in solving energy problems. Thermoelectric materials can be divided into low-temperature thermoelectric materials, medium-temperature thermoelectric materials, and high-temperature thermoelectric materials according to their working temperature. Medium-temperature thermoelectric materials have great applications in industrial waste heat recovery, automobile exhaust treatment and other fields, but the conversion efficiency restricts the practical application of thermoelectric devices. To obtain high conversion efficiency, it is necessary to have a high average ZT in the entire temperature range of 300K to 775K. GeTe has great application potential in medium-temperature thermoelectric materials. As a phase change material, GeTe undergoes a phase change at around 700K. The low temperature is the rhombohedral phase with a space group of R3m; the high temperature is the cubic phase with a space group of Fm-3m. The difference in crystal structure leads to the difference in band structure. The cubic phase GeTe is a direct band gap semiconductor, and the rhombohedral phase GeTe is an indirect band gap semiconductor. They both have multiple valence band tops with similar energies, and the energy difference between the L and Σ valence band tops of the cubic phase is lower than that of the rhombohedral phase. Due to the low formation energy of Ge vacancies in intrinsic GeTe, the presence of a large number of vacancies leads to a carrier concentration in intrinsic GeTe close to 10 21 cm -3 , much higher than 1-2×10 20 cm -3 The optimal carrier concentration is reduced, and the carrier mobility is also deteriorated. The thermoelectric figure of merit of intrinsic GeTe is only about 1. If GeTe is to be used in practice, the thermoelectric performance needs to be further improved. Existing research has difficulty in achieving performance optimization in the full temperature range of 300K to 775K. Summary of the invention

[0003] The present invention aims to solve the problem that it is difficult for existing GeTe to achieve performance optimization in the full temperature range of 300K to 775K, and further provide a high-performance p-type GeTe-based thermoelectric material and a preparation method thereof.

[0004] A high-performance p-type GeTe-based thermoelectric material, its chemical formula is 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 is carried out according to the following steps:

[0006] 1. Weighing:

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

[0008] 2. Sealing:

[0009] placing the raw material in a quartz tube and vacuum-sealing it to obtain a sealed raw material;

[0010] 3. Heating, melting and annealing:

[0011] The sealed raw materials are placed in a muffle furnace, heated and melted at a temperature of 900°C to 1000°C, then cooled and annealed at a temperature of 550°C to 650°C, and finally cooled with the furnace to obtain an ingot;

[0012] 4. Sintering:

[0013] The ingot is ground into powder, and then placed in a graphite mold for rapid hot pressing and sintering, thereby completing the preparation method of high-performance p-type GeTe-based thermoelectric materials.

[0014] The beneficial effects of the present invention are:

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

[0016] 2. In the p-type GeTe-based thermoelectric material provided by the present invention, 10% heavy element Pb doping at the Ge position significantly reduces the thermal conductivity and the carrier concentration, 6% heterovalent donor element Sb doping at the Ge position optimizes the carriers, Cd doping achieves band convergence and improves the Seebeck coefficient, and the introduction of Ge vacancies further reduces the thermal conductivity and promotes band convergence. Multiple means are synergistically optimized to make the room temperature carrier concentration 1.00×10 20 cm -3 ~3.60×10 20 cm -3 The thermal conductivity is 0.9Wm in the whole temperature range of 300K~775K -1 K -1 ~1.51Wm -1 K -1 The Seebeck coefficient is 110μVK in the full temperature range of 300K~775K -1 ~281μVK -1 , the average ZT is 1.18-1.66 in the entire temperature range of 300K-775K, and finally the highest ZT of the material is 1.9-2.3.

[0017] The invention is used for a high-performance p-type GeTe-based thermoelectric material and a preparation method thereof. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0020] Figure 3 This is a graph showing the variation of the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 1 with temperature;

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

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

[0023] Figure 6 This is a graph showing the variation of the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 2 with temperature;

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

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

[0026] Fig. 9 This is a graph showing the variation of the ZT value of the p-type GeTe-based thermoelectric material prepared in Example 3 with temperature. DETAILED DESCRIPTION

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

[0028] Specific implementation method 1: This implementation method is a high-performance p-type GeTe-based thermoelectric material, whose chemical formula is 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 embodiment is 6.18 g / cm 3 The p-type GeTe-based thermoelectric material preferably has a density of 6.2 g / cm 3 ~6.3g / cm3 .

[0030] The beneficial effects of this embodiment are:

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

[0032] 2. In the p-type GeTe-based thermoelectric material provided by the present invention, 10% heavy element Pb doping at the Ge position significantly reduces the thermal conductivity and the carrier concentration, 6% heterovalent donor element Sb doping at the Ge position optimizes the carriers, Cd doping achieves band convergence and improves the Seebeck coefficient, and the introduction of Ge vacancies further reduces the thermal conductivity and promotes band convergence. Multiple means are synergistically optimized to make the room temperature carrier concentration 1.00×10 20 cm -3 ~3.60×10 20 cm -3 The thermal conductivity is 0.9Wm in the whole temperature range of 300K~775K -1 K -1 ~1.51Wm -1 K -1 The Seebeck coefficient is 110μVK in the full temperature range of 300K~775K -1 ~281μVK -1 , the average ZT is 1.18-1.66 in the entire temperature range of 300K-775K, and finally the highest ZT of the material is 1.9-2.3.

[0033] Specific embodiment 2: This embodiment differs from specific embodiment 1 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 in the full temperature range of 300K-775K. Other aspects are the same as specific embodiment 1.

[0034] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that the density of the high-performance p-type GeTe-based thermoelectric material is ≥ 6.20 g / cm 3 The rest is the same as the first or second embodiment.

[0035] Specific embodiment 4: This embodiment is a method for preparing a high-performance p-type GeTe-based thermoelectric material, which is carried out in the following steps:

[0036] 1. Weighing:

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

[0038] 2. Sealing:

[0039] placing the raw material in a quartz tube and vacuum-sealing it to obtain a sealed raw material;

[0040] 3. Heating, melting and annealing:

[0041] The sealed raw materials are placed in a muffle furnace, heated and melted at a temperature of 900°C to 1000°C, then cooled and annealed at a temperature of 550°C to 650°C, and finally cooled with the furnace to obtain an ingot;

[0042] 4. Sintering:

[0043] The ingot is ground into powder, and then placed in a graphite mold for rapid hot pressing and sintering, thereby completing the preparation method of high-performance p-type GeTe-based thermoelectric materials.

[0044] Specific implementation method 5: This implementation method is different from specific implementation method 4 in that the purity of the raw material in step 1 is above 99.9%. The rest is the same as specific implementation method 4.

[0045] Specific implementation example 6: This implementation example is different from specific implementation example 4 or 5 in that: in step 3, the temperature is raised to 900° C. to 1000° C. within 10 h to 14 h. The rest is the same as specific implementation example 4 or 5.

[0046] Specific embodiment 7: This embodiment is different from any one of specific embodiments 4 to 6 in that: in step 3, the temperature is lowered to 550° C. to 650° C. within 4 to 6 hours. The rest is the same as specific embodiments 4 to 6.

[0047] Specific embodiment 8: This embodiment differs from any one of specific embodiments 4 to 7 in that in step 3, the annealing treatment is performed at a temperature of 550° C. to 650° C. for 48 h to 72 h. The rest is the same as specific embodiments 4 to 7.

[0048] Specific embodiment 9: This embodiment is different from specific embodiments 4 to 8 in that the rapid hot pressing sintering described in step 4 is specifically carried out according to the following steps: first evacuate to below 20Pa, then heat to 500℃~600℃ under the condition of pressure of 55MPa~65MPa, keep warm for 30min~45min under the condition of pressure of 55MPa~65MPa and temperature of 500℃~600℃, and finally air cool to room temperature without pressure. Others are the same as specific embodiments 4 to 8.

[0049] Specific embodiment 10: This embodiment is different from specific embodiments 4 to 9 in that the temperature is raised from room temperature to 500° C. to 600° C. within 2 to 8 minutes. The rest is the same as specific embodiments 4 to 9.

[0050] The following examples are used to verify the beneficial effects of the present invention:

[0051] Embodiment 1:

[0052] A method for preparing a high-performance p-type GeTe-based thermoelectric material is carried out according to the following steps:

[0053] 1. Weighing:

[0054] According to the chemical formula Ge 0.83 Pb 0.1 Sb 0.06 Cd 0.01 The amount ratio of substances in Te is as follows: Ge block, Pb pellet, Sb block, Cd pellet and Te block are weighed as raw materials;

[0055] 2. Sealing:

[0056] placing the raw material in a quartz tube and vacuum-sealing it to obtain a sealed raw material;

[0057] 3. Heating, melting and annealing:

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

[0059] 4. Sintering:

[0060] The ingot was ground into powder and then placed in a graphite mold of Φ=12.7 mm. It was first evacuated to below 20 Pa, then heated from room temperature to 550°C for 5 minutes at a pressure of 60 MPa, kept warm for 40 minutes at a pressure of 60 MPa and a temperature of 550°C, and finally air-cooled to room temperature without pressure to obtain a p-type GeTe-based thermoelectric material.

[0061] The purity of the raw material described in step 1 is above 99.9%.

[0062] Figure 1 This is the XRD spectrum of the p-type GeTe-based thermoelectric material prepared in Example 1; as can be seen from the figure, the GeTe-based thermoelectric material is single-phase;

[0063] Figure 2This is a SEM image of the p-type GeTe-based thermoelectric material prepared in Example 1; it can be seen from the image that 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 / cm 3 , the room temperature conductivity is 1158.61S / cm, and the carrier concentration is 1.66×10 20 cm -3 , the Seebeck coefficient is 128.41μV / K, and the Seebeck coefficient is positive, indicating that it is p-type. Its ZT value changes with temperature as shown in Figure 3 As shown ( Figure 3 The ZT value of the p-type GeTe-based thermoelectric material prepared in Example 1 varies with temperature. At 675K, the conductivity is 388.78 Scm -1 , the Seebeck coefficient is 276.22μVK -1 , thermal conductivity is 0.96Wm -1 K -1 , ZT can reach 2.09; the average ZT is 1.42 in the full temperature range of 300K~775K, which is a thermoelectric material with excellent performance.

[0065] Embodiment 2: This embodiment is different from the embodiment 1 in that: in step 1, according to the chemical formula Ge 0.81 Pb 0.1 Sb 0.06 Cd 0.01 The amount ratio of the substance in Te is as follows: Ge block, Pb particle, Sb block, Cd particle and Te block are weighed as raw materials. The rest is the same as in Example 1.

[0066] Figure 4 This is the XRD spectrum of the p-type GeTe-based thermoelectric material prepared in Example 2; it can be seen from the figure that the GeTe-based thermoelectric material is single-phase;

[0067] Figure 5 This is a SEM image of the p-type GeTe-based thermoelectric material prepared in Example 2; it can be seen from the figure that the GeTe-based thermoelectric material has no impurities except for the 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 / cm 3 , the room temperature conductivity is 1310.52S / cm, and the carrier concentration is 1.81×10 20 cm -3 , the Seebeck coefficient is 128.30μV / K, and the Seebeck coefficient is positive, indicating that it is p-type. Its ZT value changes with temperature as shown in Figure 6 As shown ( Figure 6The ZT value of the p-type GeTe-based thermoelectric material prepared in Example 2 varies with temperature. At 700K, the conductivity is 405.86Scm -1 , Seebeck coefficient is 280.45μVK -1 , thermal conductivity is 0.97Wm -1 K -1 , ZT can reach 2.28; the average ZT is 1.66 in the full temperature range of 300K~775K, which is a thermoelectric material with excellent performance.

[0069] Embodiment 3: This embodiment is different from the embodiment 1 in that: in step 1, according to the chemical formula Ge 0.79 Pb 0.1 Sb 0.06 Cd 0.01 The amount ratio of the substance in Te is as follows: Ge block, Pb particle, Sb block, Cd particle and Te block are weighed as raw materials. The rest is the same as in Example 1.

[0070] Figure 7 This is the XRD spectrum of the p-type GeTe-based thermoelectric material prepared in Example 3; it can be seen from the figure that the GeTe-based thermoelectric material is single-phase;

[0071] Figure 8 This is a SEM image of the p-type GeTe-based thermoelectric material prepared in Example 3; it can be seen from the image that the GeTe-based thermoelectric material has no impurities except for the 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 / cm 3 , the room temperature conductivity is 1393.72S / cm, and the carrier concentration is 3.60×10 20 cm -3 , the Seebeck coefficient is 110.62μV / K, and the Seebeck coefficient is positive, indicating that it is p-type. Its ZT value changes with temperature as shown in Fig. 9 As shown ( Fig. 9 The ZT value of the p-type GeTe-based thermoelectric material prepared in Example 3 varies with temperature. At 775K, the conductivity is 690.68Scm -1 , Seebeck coefficient is 220.65μVK -1 , thermal conductivity is 1.36Wm -1 K -1 , ZT can reach 1.91; the average ZT is 1.18 in the whole temperature range of 300K~775K, which is a thermoelectric material with excellent performance.

Claims

1. A high-performance p-type GeTe-based thermoelectric material, characterized in that Its chemical formula is Ge 0.84-x- y Pb 0.1 Sb 0.06 Cd x Te, where 0<x<0.1, 0≤y<0.

05.

2. A high performance p-type GeTe-based thermoelectric material according to claim 1, characterized 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 in the full temperature range of 300K-775K.

3. A high performance p-type GeTe-based thermoelectric material according to claim 1, characterized in that The density of the high-performance p-type GeTe-based thermoelectric material is ≥6.20 g / cm 3 .

4. A method for preparing a high-performance p-type GeTe-based thermoelectric material according to claim 1, characterized in that It is carried out in the following steps:

1. Weighing: According to the chemical formula Ge 0.84-x-y Pb 0.1 Sb 0.06 Cd x The amount ratio of substances in Te is to weigh Ge blocks, Pb particles, Sb blocks, Cd particles and Te blocks as raw materials, where 0<x<0.1, 0≤y<0.05; 2. Sealing: placing the raw material in a quartz tube and vacuum-sealing it to obtain a sealed raw material; 3. Heating, melting and annealing: The sealed raw materials are placed in a muffle furnace, heated and melted at a temperature of 900°C to 1000°C, then cooled and annealed at a temperature of 550°C to 650°C, and finally cooled with the furnace to obtain an ingot; 4. Sintering: The ingot is ground into powder, and then placed in a graphite mold for rapid hot pressing and sintering, thereby completing the preparation method of high-performance p-type GeTe-based thermoelectric materials.

5. The method for preparing a high-performance p-type GeTe-based thermoelectric material according to claim 4, characterized in that The purity of the raw material described in step 1 is above 99.9%.

6. The method for preparing a high-performance p-type GeTe-based thermoelectric material according to claim 4, characterized in that In step 3, the temperature is raised to 900°C to 1000°C within 10h to 14h.

7. The method for preparing a high-performance p-type GeTe-based thermoelectric material according to claim 4, characterized in that In step 3, the temperature is lowered to 550°C to 650°C within 4 to 6 hours.

8. The method for preparing a high-performance p-type GeTe-based thermoelectric material according to claim 4, characterized in that In step three, the annealing treatment is performed at a temperature of 550° C. to 650° C. for 48 h to 72 h.

9. The method for preparing a high-performance p-type GeTe-based thermoelectric material according to claim 4, characterized in that The rapid hot pressing sintering described in step 4 is specifically carried out according to the following steps: first evacuate to below 20Pa, then heat to 500℃~600℃ under the condition of pressure of 55MPa~65MPa, keep warm for 30min~45min under the condition of pressure of 55MPa~65MPa and temperature of 500℃~600℃, and finally cool to room temperature in air without pressure.

10. The method for preparing a high-performance p-type GeTe-based thermoelectric material according to claim 9, characterized in that The temperature is raised from room temperature to 500°C to 600°C within 2 to 8 minutes.

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