A silicon-germanium-based thermoelectric material doped with oxides and its preparation method

Abstract

This invention discloses a silicon-germanium-based thermoelectric material doped with oxides and its preparation method. The preparation method of the silicon-germanium-based thermoelectric material doped with oxides includes the following steps: (1) Under an inert atmosphere, raw materials are added to a mixing container to mix them uniformly, obtaining a uniformly mixed precursor powder; (2) The precursor powder from step (1) is pre-compacted in a mold that can apply pressure from above and below; (3) The mold containing the precursor powder is transferred to a reaction container for reaction, and after cooling, the silicon-germanium-based thermoelectric material doped with oxides is obtained. This invention comprehensively improves the performance of silicon-germanium-based thermoelectric materials by doping with a specific oxide (boron oxide) and combining it with a specific synthesis process. The silicon-germanium-based thermoelectric material prepared by this invention is easy to industrialize and can achieve a higher ZT value at lower temperatures, significantly improving its thermoelectric conversion efficiency and enabling wider applications.

Description

Technical Field

[0001] This invention relates to the field of green and environmentally friendly thermoelectric conversion materials technology, and in particular to a silicon-germanium-based thermoelectric material doped with oxides and its preparation method. Background Technology

[0002] With fossil fuels dwindling, it's becoming increasingly difficult to meet the demands of long-term sustainable development for human society. Besides developing new energy sources, another way to address the energy crisis is to improve energy efficiency. During energy use and conversion, a significant amount of energy is dissipated as heat, resulting in enormous energy waste. Thermoelectric materials have the ability to directly convert heat and electricity, offering a feasible solution to the problems of continuously increasing global energy consumption, limited fossil fuel reserves, and severe environmental pollution.

[0003] Silicon, an inorganic material, is a crucial foundational material for the semiconductor industry. Silicon-based devices boast mature and reliable processes and significant cost advantages. Germanium, possessing certain metallic properties, is classified as a semi-metallic material. Silicon-germanium composites can significantly enhance the thermoelectric performance of silicon-based materials. Traditionally, silicon-germanium thermoelectric materials belong to the category of medium-to-high temperature thermoelectric materials. Research began in the 1950s, and in 1977, the Voyager spacecraft first employed a silicon-germanium alloy as a thermoelectric power generation material. Subsequently, in NASA's space programs, silicon-germanium has essentially completely replaced lead-tellurium materials. Silicon-germanium thermoelectric conversion materials have been operating in the power supply systems of space station devices for over 40 years without failure, demonstrating the reliability of silicon-germanium-based materials.

[0004] The thermoelectric conversion efficiency of a material directly affects its energy conversion efficiency. The thermoelectric conversion efficiency is determined by the dimensionless thermoelectric figure of merit (ZT), where ZT = S. 2 σT / k, where S is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity. However, these three important parameters are interdependent, making adjustment challenging. Silicon-germanium alloys are composites of elemental silicon and elemental germanium. Both materials have relatively high power factors, but they also have relatively high thermal conductivity, thus presenting a drawback.

[0005] In recent decades, numerous studies have been conducted on how to improve the ZT value of silicon-germanium-based thermoelectric materials. Methods such as adjusting the bandgap width by changing the silicon-germanium ratio, reducing thermal conductivity by forming silicides to provide additional phonon scattering centers, dimensional reduction, and introducing nanoscale dopants have all been employed to enhance the ZT value of silicon-germanium-based thermoelectric materials. However, these methods have not yet achieved ideal results. Furthermore, most of these methods are too costly to be industrially feasible, and silicon-germanium-based thermoelectric materials often exhibit high ZT values ​​only above 800°C, which limits their applications. Therefore, silicon-germanium-based thermoelectric materials have not yet achieved widespread adoption.

[0006] In conclusion, only by adopting effective and easily implemented methods to decouple the Seebeck coefficient, electrical conductivity, and thermal conductivity of silicon-germanium-based thermoelectric materials, and significantly improve their ZT value, can silicon-germanium-based thermoelectric materials be widely applied. Furthermore, shifting the high-performance range of silicon-germanium-based thermoelectric materials from the high-temperature region to the low-temperature region, enabling them to obtain ideal ZT values ​​in the medium- and low-temperature ranges, will undoubtedly greatly expand the application scope and prospects of silicon-germanium-based thermoelectric materials. Summary of the Invention

[0007] This invention solves the aforementioned problems existing in the prior art. The purpose of this invention is to provide a silicon-germanium-based thermoelectric material doped with oxides and its preparation method. By doping with a specific oxide (boron oxide) and combining it with a specific synthesis process, the performance of the silicon-germanium-based thermoelectric material is comprehensively improved. The silicon-germanium-based thermoelectric material prepared by this invention is easy to industrialize and can achieve a higher ZT value at a lower temperature, which can significantly improve its thermoelectric conversion efficiency and obtain a wider range of applications.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: a silicon-germanium-based thermoelectric material doped with oxides, having the general formula Si 80 Ge 20 B 1～2 (B2O3) 0.1～1 .

[0009] The silicon-germanium-based thermoelectric material proposed in this invention has a high power factor and low thermal conductivity, achieving a higher ZT value at a lower temperature, which means it has higher thermoelectric conversion efficiency and can be applied in a wider range of applications.

[0010] Preferably, the density of the silicon-germanium-based thermoelectric material doped with oxides is 2.1–3.1 g / cm³. 3 .

[0011] This invention also protects a method for preparing the above-mentioned silicon-germanium-based thermoelectric material doped with oxides, comprising the following steps:

[0012] (1) Under the protection of an inert atmosphere, the raw materials are added to a mixing container, the raw materials including silicon powder, germanium powder, boron powder and boron oxide powder, so that the raw materials are mixed evenly to obtain a uniformly mixed precursor powder.

[0013] (2) The precursor powder in (1) above is loaded into a mold that can apply pressure from the top and bottom for pre-compaction;

[0014] (3) The mold containing the precursor powder is transferred to the reaction vessel for reaction. After cooling, silicon-germanium-based thermoelectric material doped with oxide is obtained.

[0015] Preferably, the raw materials mentioned in step (1) include silicon powder, germanium powder, boron powder and boron oxide powder, and the molar ratio of silicon powder, germanium powder, boron powder and boron oxide powder is 80:20:(1~2):(0.1~1).

[0016] Preferably, the specific steps of step (1) of adding raw materials to a mixing container, wherein the raw materials include silicon powder, germanium powder, boron powder and boron oxide powder, to mix the raw materials evenly and obtain a uniformly mixed precursor powder are as follows: adding raw materials to a mixing container, wherein the raw materials include silicon powder, germanium powder, boron powder and boron oxide powder, and then adding grinding media to the mixing container for ball milling to mix the raw materials evenly and obtain a uniformly mixed precursor powder.

[0017] This invention is the first to employ a method of mixing boron oxide and silicon-germanium-based materials in a specific chemical ratio, followed by a detailed ball milling and sintering process to prepare a solid block product. The silicon-germanium-based thermoelectric material prepared using this method exhibits a high power factor and low thermal conductivity, achieving a higher ZT value at lower temperatures, thus demonstrating higher thermoelectric conversion efficiency and a wider range of applications. Furthermore, the preparation method proposed in this invention is easily industrialized and has high versatility.

[0018] More preferably, the grinding media is a steel ball or zirconium ball with a regular or irregular shape, and the mass ratio of the grinding media to the raw material is 5:1 to 100:1.

[0019] Further preferably, the ball milling time is 10 to 20 hours and the rotation speed is 450 to 650 rpm.

[0020] Preferably, the pre-compaction pressure in step (2) is 1 to 5 MPa.

[0021] Preferably, step (3) involves transferring the mold containing the precursor powder into the reaction vessel and carrying out the reaction as follows: the mold containing the precursor powder is transferred into the reaction vessel, a pressure of 10 to 100 MPa is applied to both the upper and lower ends of the mold to compact the precursor powder, a vacuum is drawn to 5 to 20 Pa, and then the temperature is raised to 950 to 1200°C at a rate of 20 to 100°C / min throughout the process, and held for 1 to 30 minutes.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention prepares silicon-germanium-based thermoelectric materials with better thermoelectric performance through specific chemical ratios and appropriate processes. At 600℃, its Seebeck coefficient is 239~258μV / K, resistivity is 14.2~16.9μΩ·m, thermal conductivity is 2.5~3.5W / mK, and ZT value is 0.97~1.47. The thermoelectric performance is significantly higher than that of existing silicon-germanium-based thermoelectric materials, and the applicable temperature is reduced, making it more universal. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the preparation process of the silicon-germanium-based thermoelectric material doped with oxides proposed in this invention.

[0024] Figure 2 The thermoelectric performance curve of the silicon-germanium-based thermoelectric material obtained in Example 1 is shown.

[0025] Figure 3 The thermoelectric performance curve of the silicon-germanium-based thermoelectric material obtained in Example 2 is shown in the figure.

[0026] Figure 4 The thermoelectric performance curve of the silicon-germanium-based thermoelectric material obtained in Example 3 is shown in the figure.

[0027] Figure 5 The graph shows the thermoelectric performance of the silicon-germanium-based thermoelectric material obtained in Comparative Example 1. Detailed Implementation

[0028] The following embodiments are further illustrations of the present invention, but not limitations thereof. Unless otherwise specified, the equipment and reagents used in the present invention are commercially available products conventional in this technical field.

[0029] A method for preparing a silicon-germanium-based thermoelectric material doped with oxides includes the following steps:

[0030] (1) Under the protection of an inert atmosphere, the raw materials are added to a mixing container. The raw materials include silicon powder, germanium powder, boron powder and boron oxide powder. The raw materials are mixed evenly to obtain a uniformly mixed precursor powder.

[0031] (2) The precursor powder in (1) above is loaded into a mold that can apply pressure from the top and bottom for pre-compaction;

[0032] (3) Transfer the mold containing the precursor powder to a spark plasma sintering furnace or other sintering equipment with vacuum and pressure, react, and after cooling, obtain silicon-germanium-based thermoelectric material doped with oxides.

[0033] In the following embodiments, it is preferred that the raw materials in step (1) include silicon powder, germanium powder, boron powder and boron oxide powder, and the molar ratio of silicon powder, germanium powder, boron powder and boron oxide powder is 80:20:(1~2):(0.1~1).

[0034] The methods of uniform mixing include, but are not limited to, mechanical bearing-type stirring dispersion, homogenization dispersion, sand milling and other forms of mixing dispersion, which will not be listed here. Those skilled in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention. In the following embodiments, ball milling is preferred for uniform mixing.

[0035] In the following preferred embodiments, step (1), which involves adding the raw materials to a mixing container to achieve uniform mixing and obtain a uniformly mixed precursor powder, specifically involves adding the raw materials to the mixing container, then adding grinding media to the mixing container and performing ball milling using a horizontal or vertical planetary ball mill to achieve uniform mixing and obtain a uniformly mixed precursor powder. More preferably, the grinding media are regular or irregularly shaped steel balls or zirconium balls, the mass ratio of the grinding media to the raw materials is 5:1 to 100:1, the ball milling time is 10 to 20 hours, and the rotation speed is 450 to 650 rpm.

[0036] In the following embodiments, it is preferred that the pre-compaction pressure in step (2) is 1 to 5 MPa.

[0037] In the preferred embodiment below, step (3) involves transferring the mold containing the precursor powder into the reaction vessel and carrying out the reaction as follows: the mold containing the precursor powder is transferred into the reaction vessel, a pressure of 10 to 100 MPa is applied to both the upper and lower ends of the mold to compact the precursor powder, a vacuum is drawn to 5 to 20 Pa, and then the temperature is raised to 950 to 1200°C at a rate of 20 to 100°C / min throughout the process, and held at that temperature for 1 to 30 minutes.

[0038] The cooling method is to cool the furnace after sintering or to accelerate or delay cooling through gas, liquid or other media.

[0039] The silicon-germanium-based thermoelectric material with doped oxides prepared by the above method has a density of 2.1–3.1 g / cm³. 3 The geometric shapes include, but are not limited to, cuboids, cylinders, cones, or irregular polyhedra.

[0040] Example 1

[0041] like Figure 1 As shown, the preparation method of silicon-germanium-based thermoelectric materials doped with oxides includes the following steps:

[0042] (1) Under the protection of argon atmosphere, the raw materials were weighed according to the stoichiometric ratio, and Si was prepared according to the molar ratio. 80 Ge 20 B1(B2O3) 0.1 Mix the powder and load it into a sealable ball mill jar. Add steel balls in a 5:1 ratio with the powder. Seal the ball mill jar in an argon atmosphere to protect the powder and steel balls.

[0043] (2) Transfer the ball mill jar containing powder and steel balls from step (1) to a horizontal planetary ball mill. The ball milling time is 10 hours and the speed is 450 rpm.

[0044] (3) After ball milling, transfer the ball milling jar to an argon-protected environment, load the uniformly mixed powder into a mold that can apply pressure from the top and bottom to compact the powder, and use a press to pre-compact it with a pre-compression pressure of 1 MPa.

[0045] (4) Transfer the mold containing the powder to the spark plasma sintering furnace, apply a pressure of 10 MPa to the top and bottom of the mold to compact the powder, and evacuate to 5 Pa. Then, raise the temperature to 950°C at a rate of 20°C / min throughout the process, hold for 1 minute, and remove the block product after cooling in the furnace (the block product can be formed into any geometric shape according to the mold).

[0046] The density of the finished block was tested using Archimedes' displacement method, and the density was 2.1 g / cm³. 3 According to the requirements of the testing equipment, it was cut into cuboids for thermoelectric performance testing, and the results are as follows. Figure 2 As shown.

[0047] from Figure 2 Test results show that the thermoelectric properties of the finished product prepared by the method of this invention increase with increasing temperature. At 600℃, its Seebeck coefficient is 258 μV / K, resistivity is 16.9 μΩ·m, thermal conductivity is 3.5 W / mK, and ZT value is 0.97. The thermoelectric performance is significantly higher than that of existing silicon-germanium-based thermoelectric materials, and the applicable temperature is lowered, thus improving its versatility.

[0048] Example 2

[0049] like Figure 1 As shown, the preparation method of silicon-germanium-based thermoelectric materials doped with oxides includes the following steps:

[0050] (1) Under the protection of argon atmosphere, the raw materials were weighed according to the stoichiometric ratio, and Si was prepared according to the molar ratio. 80 Ge 20 B 1.5 (B2O3) 0.6 Mix the powder and load it into a sealable ball mill jar. Add steel balls at a mass ratio of 20:1 (steel balls to mixed powder). Seal the ball mill jar in an argon atmosphere to protect the powder and steel balls under the argon atmosphere.

[0051] (2) Transfer the ball mill jar containing powder and steel balls from (1) above to a horizontal planetary ball mill. The ball milling time is 15 hours and the speed is 550 rpm.

[0052] (3) After ball milling is completed, the ball milling jar is transferred to an argon-protected environment. The powder that has been ball-milled and mixed evenly is loaded into a mold that can apply pressure from the top and bottom to compact the powder. A press is used for pre-compaction, with a pre-compression pressure of 2.5 MPa.

[0053] (4) Transfer the mold containing the powder to the spark plasma sintering furnace, apply a pressure of 50 MPa to the top and bottom of the mold to compact the powder, and evacuate to 10 Pa. Then, raise the temperature to 1100℃ at a heating rate of 60℃ / min throughout the process, hold for 3 minutes, and remove the block product after cooling in the furnace (the block product can be formed into any geometric shape according to the mold).

[0054] The density of the finished block was tested using Archimedes' displacement method and found to be 2.6 g / cm³. 3 According to the requirements of the testing equipment, it was cut into cuboids for thermoelectric performance testing, and the results are as follows. Figure 3 As shown.

[0055] from Figure 3 Test results show that the thermoelectric properties of the finished product prepared by the method of this invention increase with increasing temperature. At 600℃, its Seebeck coefficient is 250 μV / K, resistivity is 15.0 μΩ·m, thermal conductivity is 2.5 W / mK, and ZT value is 1.47. The thermoelectric performance is significantly higher than that of existing silicon-germanium-based thermoelectric materials, and the applicable temperature is lowered, thus improving its versatility.

[0056] Example 3

[0057] like Figure 1 As shown, the preparation method of silicon-germanium-based thermoelectric materials doped with oxides includes the following steps:

[0058] (1) Under the protection of argon atmosphere, the raw materials were weighed according to the stoichiometric ratio, and Si was prepared according to the molar ratio. 80 Ge 20 The B2(B2O3)1 mixed powder was placed in a sealable ball mill jar, and steel balls were added. The ratio of steel balls to mixed powder was 100:1. The ball mill jar was sealed in an argon atmosphere to protect the powder and steel balls.

[0059] (2) Transfer the ball mill jar containing powder and steel balls from (1) above to a horizontal planetary ball mill. The ball milling time is 20 hours and the speed is 650 rpm.

[0060] (3) After ball milling is completed, the ball milling jar is transferred to an argon-protected environment. The powder that has been ball-milled and mixed evenly is loaded into a mold that can apply pressure from the top and bottom to compact the powder. A press is used for pre-compaction, and the pre-compression pressure is 5 MPa.

[0061] (4) Transfer the mold containing the powder to the spark plasma sintering furnace, apply a pressure of 100MPa to the top and bottom of the mold to compact the powder, and evacuate to 20Pa. Then, raise the temperature to 1200℃ at a heating rate of 100℃ / min throughout the process, hold for 30 minutes, and remove the block product after cooling in the furnace (the block product can be formed into any geometric shape according to the mold).

[0062] The density of the finished block was tested using Archimedes' displacement method and found to be 3.1 g / cm³. 3 According to the requirements of the testing equipment, it was cut into cuboids for thermoelectric performance testing, and the results are as follows. Figure 4 As shown.

[0063] from Figure 4 Test results show that the thermoelectric properties of the finished product prepared by the method of this invention increase with increasing temperature. At 600℃, its Seebeck coefficient is 239 μV / K, resistivity is 14.2 μΩ·m, thermal conductivity is 2.6 W / mK, and ZT value is 1.36. The thermoelectric performance is significantly higher than that of existing silicon-germanium-based thermoelectric materials, and the applicable temperature is lowered, thus improving its versatility.

[0064] Comparative Example 1

[0065] A method for preparing silicon-germanium-based thermoelectric materials without oxide doping includes the following steps:

[0066] (1) Under the protection of argon atmosphere, the raw materials were weighed according to the stoichiometric ratio, and Si was prepared according to the molar ratio. 80 Ge 20 B 1.5 Mix the powder and load it into a sealable ball mill jar. Add steel balls in a 20:1 ratio with the powder mixture. Seal the ball mill jar in an argon atmosphere to protect the powder and steel balls.

[0067] (2) Transfer the ball mill jar containing powder and steel balls from (1) above to a horizontal planetary ball mill. The ball milling time is 15 hours and the speed is 550 rpm.

[0068] (3) After ball milling is completed, the ball milling jar is transferred to an argon-protected environment. The powder that has been ball-milled and mixed evenly is loaded into a mold that can apply pressure from the top and bottom to compact the powder. A press is used for pre-compaction, with a pre-compression pressure of 2.5 MPa.

[0069] (4) Transfer the mold containing the powder to the spark plasma sintering furnace, apply a pressure of 50 MPa to the top and bottom of the mold to compact the powder, and evacuate to 10 Pa. Then, raise the temperature to 1100℃ at a heating rate of 60℃ / min throughout the process, hold for 30 minutes, and remove the block product after cooling in the furnace (the block product can be formed into any geometric shape according to the mold).

[0070] The density of the finished block was tested using Archimedes' displacement method and found to be 2.0 g / cm³. 3 According to the requirements of the testing equipment, it was cut into cuboids for thermoelectric performance testing, and the results are as follows. Figure 5 As shown.

[0071] from Figure 5 The test results show that the thermoelectric properties of the product prepared by the method of this invention increase with increasing temperature. At 600℃, its Seebeck coefficient is 220 μV / K, resistivity is 13.8 μΩ·m, thermal conductivity is 4.2 W / mK, and ZT value is only 0.74. It can be clearly seen that the ZT value of the sample without B2O3 doping is significantly lower.

[0072] In summary, the preparation method provided by this invention adopts a one-step ball milling method combined with rapid pressure sintering, which has a simple process flow, is easy to industrialize, and has broad prospects.

[0073] The above embodiments are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A silicon-germanium-based thermoelectric material doped with oxides, characterized in that, Its general formula is Si 80 Ge 20 B 1～2 (B2O3) 0.1～1 ; The method for preparing the silicon-germanium-based thermoelectric material doped with oxides includes the following steps: (1) Under an inert atmosphere, the raw materials are added to a mixing container. The raw materials include silicon powder, germanium powder, boron powder and boron oxide powder. The molar ratio of silicon powder, germanium powder, boron powder and boron oxide powder is 80:20:(1~2):(0.1~1) to make the raw materials mix evenly and obtain a uniformly mixed precursor powder. (2) The precursor powder in (1) above is loaded into a mold that can apply pressure from the top and bottom for pre-compaction; (3) Transfer the mold containing the precursor powder to the reaction vessel, apply a pressure of 10 to 100 MPa to the upper and lower ends of the mold to compact the precursor powder, evacuate to 5 to 20 Pa, and then heat to 950 to 1200 °C at a heating rate of 20 to 100 °C / min throughout the process, hold for 1 to 30 minutes, and after cooling, obtain silicon germanium-based thermoelectric material doped with oxide.

2. The silicon-germanium-based thermoelectric material with doped oxides according to claim 1, characterized in that, The density of the silicon-germanium-based thermoelectric material doped with oxides is 2.1–3.1 g / cm³. 3 .

3. The silicon-germanium-based thermoelectric material with doped oxides according to claim 1, characterized in that, Step (1) involves adding raw materials to a mixing container, including silicon powder, germanium powder, boron powder and boron oxide powder, to mix the raw materials evenly and obtain a uniformly mixed precursor powder. The specific steps are as follows: add the raw materials to a mixing container, including silicon powder, germanium powder, boron powder and boron oxide powder, and then add grinding media to the mixing container for ball milling to mix the raw materials evenly and obtain a uniformly mixed precursor powder.

4. The silicon-germanium-based thermoelectric material with doped oxides according to claim 3, characterized in that, The grinding media are steel balls or zirconium balls of regular or irregular shape, and the mass ratio of grinding media to raw materials is 5:1 to 100:

1.

5. The silicon-germanium-based thermoelectric material with doped oxides according to claim 3, characterized in that, The ball milling time is 10 to 20 hours, and the rotation speed is 450 to 650 rpm.

6. The silicon-germanium-based thermoelectric material with doped oxides according to claim 1, characterized in that, The pre-compaction pressure in step (2) is 1-5 MPa.

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