Method for increasing room-temperature thermoelectric figure of merit of silver telluride

Abstract

The invention relates to a method for increasing the room-temperature thermoelectric figure of merit of silver telluride, and belongs to the technical field of thermoelectric materials. When the silver telluride is used as a thermoelectric material, a magnetic field perpendicular to the heat flow direction is applied to the silver telluride; the composition of the silver telluride is Ag < 2 + x > Te, wherein 0 lt; x is less than or equal to 0.1; the heat flow direction is the direction in which heat flows from the high-temperature end to the low-temperature end. The method is easy and convenient to implement, miscellaneous element doping modification does not need to be carried out on the material, and the mechanical strength of the material is reserved; according to the method, the room-temperature thermoelectric figure of merit of the silver telluride material can be remarkably improved.

Description

Technical Field

[0001] The invention relates to a method for improving the room temperature thermoelectric figure of merit of silver telluride, and belongs to the technical field of thermoelectric materials. Background Art

[0002] With the improvement of social development, the degree of intelligence of devices and components is gradually deepening. On the one hand, there is an increasing demand for miniaturized and portable refrigeration devices; on the other hand, for small devices such as distributed sensors that are not convenient to power, small power generation devices that can provide stable and long-term power supply also have an increasing market demand. For the above two aspects, thermoelectric technology can provide excellent solutions. On the one hand, the Peltier effect can be used to use electrical energy for cooling; on the other hand, for areas with stable temperature differences nearby, such as factory exhaust pipes, car exhaust pipes, human bodies, etc., the Seebeck effect can be used to convert thermal energy into electrical energy for use by other devices. Therefore, the development of thermoelectric technology will be of great significance to the future development of the intelligent Internet of Things.

[0003] The application of thermoelectric technology depends on thermoelectric devices. Thermoelectric devices are mainly composed of semiconductor materials, which have the characteristics of no mechanical structure, no noise and small size. The most important part is the thermoelectric material, which is divided into n-type and p-type. The thermoelectric figure of merit (ZT) of the thermoelectric material plays a decisive role in the performance of a thermoelectric device. The most widely used n-type room-temperature thermoelectric material is BiSbTe-based material. Its thermoelectric performance is high, but it is brittle and has poor mechanical processing performance. Silver chalcogenide materials usually have better mechanical processing performance and even have certain ductility, but poor thermoelectric performance. Therefore, developing new methods to improve the room-temperature thermoelectric figure of merit of silver telluride is of great significance to the development of room-temperature thermoelectric technology. Summary of the invention

[0004] In response to the above technical problems, the present invention provides a synergistic optimization method for improving the room temperature thermoelectric figure of merit of silver telluride. Through the synergistic effect of element ratio optimization and the application of a magnetic field in a direction perpendicular to the heat flow direction, the thermoelectric figure of merit ZT can be improved at room temperature. At the same time, the material is not doped with elements other than its own (silver, tellurium), thereby retaining the mechanical strength of the material itself.

[0005] In the present invention, the element ratio of the intrinsic material is optimized first, and then a magnetic field perpendicular to the heat flow direction is applied to the optimized material. The expression of the thermoelectric figure of merit is ZT = (S 2(S·T) / (κ·ρ). Except for the absolute temperature T, the other three parameters are closely related to the microscopic electronic structure such as the carrier concentration. Therefore, simply pursuing an increase in a certain parameter cannot improve the overall thermoelectric figure of merit. In the present invention, through the synergistic effect of two means, the thermoelectric potential (S) of the intrinsic material is increased, the resistivity (ρ) is decreased, and the thermal conductivity (κ) is greatly reduced, so that a significant increase in the material ZT can be achieved.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a method for improving the room temperature thermoelectric figure of merit of silver telluride. The method is: when silver telluride is used as a thermoelectric material, a magnetic field perpendicular to the heat flow direction is applied to it; the silver telluride has a composition of Ag 2+x Te, where 0 < x ≤ 0.1; the heat flow direction is the direction in which heat flows from the high temperature end to the low temperature end.

[0008] In the above technical solution, further, the magnetic induction intensity of the magnetic field is y, 0T < y ≤ 13T.

[0009] In the above technical solution, further, the preparation method of the silver telluride includes the following steps:

[0010] A. Weigh silver and tellurium elements according to the ratio, place them in a quartz tube, vacuum seal the tube, then place it in a tube furnace for melting reaction, and then quench with ice water;

[0011] B. After complete cooling, place it in the tube furnace again for annealing, and then cool naturally;

[0012] C. After taking out the bulk, remove the surface precipitates, grind it into powder, and then perform hot pressing to form a sheet;

[0013] D. Cut the material into the required size by wire cutting.

[0014] In the above technical solution, further, in step A, the vacuum degree of the quartz tube vacuum sealing is lower than 10 Pa, the melting reaction temperature is 900 °C - 1200 °C, the heat preservation time is 8 h - 12 h, and the quenching time is 6 h - 12 h.

[0015] In the above technical solution, further, in step B, the annealing temperature is 400 °C - 600 °C, and the annealing time is 24 h - 72 h.

[0016] In the above technical solution, further, in step C, during hot pressing, the applied pressure is 50 MPa - 80 MPa, the sheet forming temperature is 400 °C - 600 °C, and the heat preservation time is 5 min - 10 min.

[0017] Another aspect of the present invention provides an application of the above-mentioned method for improving the room temperature thermoelectric figure of merit of silver telluride, which is used in a portable thermoelectric cooling device and a human body temperature difference power generation and energy supply device.

[0018] The beneficial effects of the present invention are:

[0019] 1. The method of the present invention is easy to implement and does not require the material itself to be doped with elements other than its own (silver, tellurium), thereby retaining the mechanical strength of the material itself.

[0020] 2. The method of the present invention can significantly improve the room temperature thermoelectric figure of merit of silver telluride materials.

[0021] 3. The preparation method of silver telluride of the present invention is simple and efficient, which is conducive to the mass production of silver telluride materials with a fixed ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the process of the present invention;

[0023] Figure 2 The test results of the room temperature (300K) thermoelectric figure of merit (ZT) of the intrinsic material of the present invention, comparative example 1, comparative example 2 and embodiment 1;

[0024] Figure 3 The room temperature (300K) resistivity (ρ) test results of the intrinsic material of the present invention, comparative example 1, comparative example 2 and embodiment 1;

[0025] Figure 4 The test results of Seebeck coefficient (S) at room temperature (300K) of the intrinsic material of the present invention, comparative example 1, comparative example 2 and embodiment 1;

[0026] Figure 5 The room temperature (300K) thermal conductivity (κ) test results of the intrinsic material of the present invention, comparative example 1, comparative example 2 and embodiment 1. DETAILED DESCRIPTION

[0027] The following are specific embodiments of the present invention, but the invention is by no means limited to these embodiments.

[0028] Example 1

[0029] The preparation method of the silver telluride material provided in Example 1 is as follows:

[0030] (1)According to Ag ratio 2.06 Weigh the bulk material and place it in a quartz tube. After the vacuum degree reaches below 10Pa, seal the tube with vacuum. After checking the airtightness, place it in a tube furnace, melt and react at 1000℃ for 12h, and then quench in ice water.

[0031] (2) After complete cooling, the tube was placed in a tube furnace again, annealed at 420°C for 72 h, and then cooled naturally;

[0032] (3) After removing the block, remove the surface precipitates, grind it into powder manually, and then add Ag 2.06 Te powder was placed in a graphite mold and hot pressed at 420 °C for 10 min and a pressure of 50 MPa;

[0033] (4) After cooling and taking out, the material is cut into required size by wire cutting.

[0034] like Figure 1 As shown, the Ag prepared by the above method 2.06 Copper electrodes are installed at both ends of the Te material to measure the temperatures T1 and T2 (T1 ≥ T2) at both ends of the material, as well as the potential difference U generated at both ends of the material, to determine the direction of heat flow. Figure 1 From left to right, a uniform magnetic field is applied perpendicular to the direction of heat flow. The magnetic induction intensity is 9T.

[0035] After implementing the above method, measure Ag 2.06 Resistivity, Seebeck coefficient and conductivity of Te material; the resistivity is calculated by measuring the current (I), the corresponding potential difference between the two ends of the material (U) and the geometric parameters of the material; the Seebeck coefficient is calculated by the temperature difference between the two ends of the material (ΔT=T1-T2) and the corresponding potential difference between the two ends (U); the thermal conductivity is obtained by fitting the function of the change of T1 and T2 with time after a certain heat flow is given at one end of the material.

[0036] like Figure 2-5 As shown, it can be seen that at room temperature 300K, the Ag in Example 1 2.06 Te material ZT reached 0.74, resistivity was 1.26 mΩcm, and Seebeck coefficient was -130 μV K -1 , thermal conductivity is 0.54W m -1 K -1 .

[0037] Comparative Example 1

[0038] The difference from Example 1 is that the magnetic induction intensity is 0 T, that is, no magnetic field is applied, and only the element ratio of the intrinsic material Ag2Te is optimized. The other contents are the same as Example 1.

[0039] like Figure 2-5 As shown, it can be seen that at room temperature 300K, the Ag in comparative example 1 2.06 The Te material has a ZT of 0.38, a resistivity of 0.66 mΩcm, and a Seebeck coefficient of -94 μV K -1 ; Thermal conductivity is 1.08W m -1 K-1 .

[0040] Comparative Example 2

[0041] A magnetic field (9 T) of the same magnitude as in Example 1 was directly applied to the intrinsic material Ag2Te to test the thermoelectric figure of merit ZT.

[0042] like Figure 2-5 As shown, it can be seen that at room temperature 300K, the Ag in comparative example 1 2.06 The Te material has a ZT of 0.22, a resistivity of 4 mΩcm, and a Seebeck coefficient of -134 μV K -1 ; Thermal conductivity is 0.6W m -1 K -1 .

[0043] Result analysis:

[0044] According to the definition of thermoelectric figure of merit (ZT = (S 2 ·T) / (κ·ρ)), it can be seen that at the same temperature (T), the increase of Seebeck coefficient (S) and the decrease of resistivity (ρ) and thermal conductivity (κ) are beneficial to the improvement of ZT.

[0045] In comparative example 1, we reduced the resistivity and slightly lowered the thermal conductivity by optimizing the element ratio, which is beneficial to the improvement of ZT. However, the Seebeck coefficient was slightly reduced, which is not conducive to the improvement of ZT. In summary, the ZT value was slightly improved from 0.13 to 0.38.

[0046] In Comparative Example 2, we directly applied a 9T magnetic field to the intrinsic material, which increased the Seebeck coefficient and reduced the thermal conductivity, which is beneficial to the improvement of ZT. However, due to the magnetic resistance of the material, the resistivity in Comparative Example 2 increased a lot, which is not conducive to the improvement of ZT. In summary, the ZT value has also been improved to a certain extent, from 0.13 to 0.22.

[0047] In Example 1, we comprehensively utilize the two methods of Comparative Example 1 and Comparative Example 2 to optimize the element ratio and exert synergistic effects on the magnetic field, ultimately reducing the resistivity, increasing the Seebeck coefficient, and reducing the thermal conductivity, which are all changes that are beneficial to the improvement of ZT. Finally, the ZT value of the material was increased from 0.13 to 0.76.

[0048] Within the technical field of the invention, several equivalent substitutions or obvious modifications may be made without departing from the technical solution of the invention, and all of them should be deemed to belong to the protection scope of the invention.

Claims

1. A method for improving the room temperature thermoelectric figure of merit of silver telluride, characterized in that: The method is as follows: when silver telluride is used as a thermoelectric material, a magnetic field perpendicular to the direction of heat flow is applied thereto; the silver telluride has a composition of Ag 2+x Te, where 0 < x ≤ 0.1; the direction of heat flow is the direction in which heat flows from the high-temperature end to the low-temperature end.

2. The method for improving the room temperature thermoelectric figure of merit of silver telluride according to claim 1, characterized in that: The magnetic induction intensity of the magnetic field is y,0T <y≤13T。 3. The method for improving the room temperature thermoelectric figure of merit of silver telluride according to claim 1, characterized in that: The preparation method of silver telluride comprises the following steps: A. Weigh silver and tellurium in proportion and place them in a quartz tube. After vacuum sealing, place the tube in a tube furnace for melting reaction, and then quench with ice water. B. After complete cooling, place in a tube furnace for annealing again, and then cool naturally; C. After taking out the block, remove the surface precipitates, grind it into powder, and then hot press it into tablets; D. Cut the material into required size by wire cutting.

4. The method for improving the room temperature thermoelectric figure of merit of silver telluride according to claim 3, characterized in that: In step A, the vacuum degree of the quartz tube vacuum seal is lower than 10Pa, the temperature of the melting reaction is 900°C-1200°C, the insulation time is 8h-12h, and the quenching time is 6h-12h.

5. The method for improving the room temperature thermoelectric figure of merit of silver telluride according to claim 3, characterized in that: In step B, the annealing temperature is 400° C.-600° C., and the annealing time is 24 h-72 h.

6. The method for improving the room temperature thermoelectric figure of merit of silver telluride according to claim 3, characterized in that: In step C, during hot pressing, the applied pressure is 50 MPa-80 MPa, the tableting temperature is 400° C.-600° C., and the holding time is 5 min-10 min.

7. An application of the method for improving the room temperature thermoelectric figure of merit of silver telluride according to any one of claims 1 to 6, characterized in that: Used in portable thermoelectric cooling devices and human body temperature difference power generation and energy supply devices.

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