A silver-based chalcogenide thermoelectric material, its preparation method and application

Abstract

The present invention discloses a silver chalcogenide thermoelectric material, a preparation method thereof and an application. The chemical formula of the silver chalcogenide thermoelectric material is Ag 2‑δ S x Se y Te z , where δ = 0 to 0.05, x = 0.25 to 0.8, y = 0 to 0.5, z = 0.3 to 0.7, and x + y + z = 1. The silver chalcogenide thermoelectric material in the present invention is a cubic structure quaternary compound with a special body-centered cubic crystal structure, and has excellent plasticity and deformation ability while ensuring thermoelectric performance. The preparation method of the silver chalcogenide thermoelectric material in the present invention has rich raw material sources, low cost, simple production process and production equipment, and good controllability and repeatability; among them, a dense ingot can be directly obtained after melting and annealing of the initial raw materials, without steps such as sintering, which simplifies and optimizes the preparation steps and process, and saves costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric materials, and particularly relates to a silver-based chalcogenide thermoelectric material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the existence of the Seebeck effect and the Peltier effect, thermoelectric materials can achieve the mutual conversion of electrical energy and thermal energy, and are applied in many fields such as micro-region heat dissipation or refrigeration, waste heat power generation, etc. They can also collect and utilize a large amount of lost energy during the energy conversion and use process, bringing a large amount of economic benefits by using waste heat, and are a very promising clean energy. Thermoelectric materials are a kind of solid energy conversion materials, and the key advantages include environmental friendliness, high reliability, small size, and noiselessness, and partial commercialization has been achieved. Wearable flexible thermoelectric materials are a very promising energy harvesting material, which can generate electricity through the temperature difference between the human body and the environment, directly perform thermoelectric conversion, and the thermoelectric performance of the material is evaluated by the dimensionless figure of merit ZT = α 2 σTκ -1 where α, σ, and κ are the Seebeck coefficient, conductivity, and thermal conductivity of the material respectively, and T is the absolute temperature. Currently, most of the thermoelectric materials that have been applied are metal-based compounds and their solid solutions, such as Bi 2 Te 3 , PbTe, etc., but the preparation conditions of these thermoelectric materials are relatively high, and they contain heavy metals harmful to the human body. More importantly, the existing thermoelectric materials are brittle at room temperature, easy to break, and cannot undergo plastic deformation. Unless they are extremely thin, the materials do not have good flexibility and bending performance, and it is difficult to meet the requirement of closely fitting the surface of a heat source with a changing curvature; at the same time, due to their intrinsic brittleness, the samples are extremely prone to damage during the process of fine processing and daily use. Therefore, researchers have explored and developed a variety of conductive polymer-based polymer thermoelectric materials or organic-inorganic composite materials. However, the carrier mobility in organic materials is generally low, resulting in poor thermoelectric performance. For decades, scientific researchers have been constantly exploring and discovering high-performance flexible and plastic inorganic thermoelectric materials. Summary of the Invention

[0003] The present invention provides a silver-based chalcogenide thermoelectric material, a preparation method thereof, and an application thereof, which can solve the above-mentioned defects in the prior art.

[0004] In the first aspect of the present invention, a silver-based chalcogenide thermoelectric material is provided, and the chemical formula of the silver-based chalcogenide thermoelectric material is Ag 2-δ S x Se y Te z , where δ = 0 to 0.05, x = 0.25 to 0.8, y = 0 to 0.5, z = 0.3 to 0.7, and x + y + z = 1.

[0005] In one embodiment of the present invention, the thermoelectric material is an n-type thermoelectric material having a cubic crystal structure.

[0006] The second aspect of the present invention provides a method for preparing the above silver-based chalcogenide thermoelectric material, including:

[0007] According to the chemical formula Ag 2-δ S x Se y Te z Weigh Ag, S, Se and Te elemental substances, mix them as the initial raw materials, and vacuum package them in a quartz tube;

[0008] The initial raw materials are subjected to high-temperature melting reaction, and then cooled to room temperature to obtain the silver-based chalcogenide thermoelectric material.

[0009] In one embodiment of the present invention, the purity of the Ag elemental substance is 99.9% or more, the purity of the S elemental substance is 99.9% or more, the purity of the Se elemental substance is 99.9% or more, and the purity of the Te elemental substance is 99.9% or more.

[0010] In one embodiment of the present invention, after the initial raw materials are loaded into a crucible, they are vacuum packaged in a quartz tube.

[0011] In one embodiment of the present invention, the crucible is a polycrystalline boron nitride crucible, and the vacuum packaging is carried out by plasma or a flame gun in an argon atmosphere glove box.

[0012] In one embodiment of the present invention, when the initial raw materials are packaged in a quartz tube, the internal pressure is evacuated to 0.1-10 Pa.

[0013] In one embodiment of the present invention, the high-temperature melting reaction is carried out in a vertical furnace.

[0014] In one embodiment of the present invention, the high-temperature melting reaction specifically includes the following steps: heating to 900-1100 °C within 24 hours, holding for 24 hours, cooling to 700-850 °C within 12 hours, holding for 15-20 hours, then cooling to 400-500 °C, holding for 72 hours, and finally cooling to room temperature at a rate of 100-150 °C / h.

[0015] The third aspect of the present invention provides the application of the above silver-based chalcogenide thermoelectric material in thermoelectric power generation, thermoelectric refrigeration and flexible electronics, such as wearable flexible thermoelectric devices, shaped thermoelectric devices, micro thermoelectric devices, pipeline temperature sensors, etc.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. The silver-based chalcogenide thermoelectric material provided by the embodiment of the present invention is a cubic quaternary compound with a special body-centered cubic crystal structure, having excellent plasticity and deformation ability while ensuring thermoelectric performance. The silver-based chalcogenide thermoelectric material provided by the present invention did not crack in both the three-point bending test and the compression test. The maximum compression strain obtained under the test conditions is 85%, and the maximum bending strain is 35%, far superior to the existing silver sulfide-based inorganic thermoelectric materials.

[0018] 2. The preparation method of the silver-based chalcogenide thermoelectric material provided by the embodiment of the present invention has rich raw material sources, low cost, simple production process and production equipment, and good controllability and repeatability. Among them, a dense ingot can be directly obtained after the initial raw materials are melted and annealed, without steps such as sintering, streamlining and optimizing the preparation steps and processes, and saving costs.

[0019] 3. The silver-based chalcogenide thermoelectric material provided by the embodiment of the present invention can be applied to thermoelectric devices, including conventional, flexible, special-shaped and micro thermoelectric power generation or thermoelectric refrigeration devices, such as wearable flexible thermoelectric devices, special-shaped thermoelectric devices, micro thermoelectric devices, pipeline temperature sensors, etc., providing new ideas and directions for the research of thermoelectric devices.

[0020] 4. The silver-based chalcogenide thermoelectric material provided by the embodiment of the present invention is suitable for thermoelectric power generation or thermoelectric refrigeration in the medium and low temperature regions, can be used for precision machining, preparing thermoelectric devices of various different shapes and sizes, can effectively utilize low-density heat sources, and achieve the purpose of energy conservation and emission reduction to a certain extent.

[0021] 5. The silver-based chalcogenide thermoelectric material provided by the embodiment of the present invention has excellent performance, can undergo plastic deformation at room temperature, and has an extremely low thermal conductivity. Brief Description of the Drawings

[0022] Figure 1 is a schematic flow chart of the preparation method of the present invention.

[0023] Figure 2 is the X-ray diffraction (XRD) pattern of each silver-based chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ,Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 ,Ag 2 S 0.40 Se 0.34 Te 0.26 ) bulk.

[0024] Figure 3 are the thermoelectric and mechanical properties of the silver chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ) in one embodiment of the present invention. Among them, Figure 3 (a) is the electrical conductivity of the silver chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ); Figure 3 (b) is the Seebeck coefficient of the silver chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ); Figure 3 (c) is the thermal conductivity of the silver chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ), Figure 3 (d) is the thermoelectric figure of merit ZT of the silver chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ), Figure 3 (e) is the compression curve of the silver chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ), Figure 3 (f) is the bending curve of the silver chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ).

[0025] Figure 4 are the thermoelectric and mechanical properties of the silver chalcogenide thermoelectric material (Ag 2 S 0.40 Se 0.34 Te 0.26 ) in one embodiment of the present invention. Among them, Figure 4 (a) is the electrical conductivity of the silver chalcogenide thermoelectric material (Ag 2 S 0.40 Se 0.34 Te 0.26 ); Figure 4 (b) is the Seebeck coefficient of the silver chalcogenide thermoelectric material (Ag 2 S 0.40 Se 0.34 Te 0.26the Seebeck coefficient; Figure 4 (c) is the thermal conductivity of the silver-based chalcogenide thermoelectric material (Ag 2 S 0.40 Se 0.34 Te 0.26 ); Figure 4 (d) is the thermoelectric figure of merit ZT of the silver-based chalcogenide thermoelectric material (Ag 2 S 0.40 Se 0.34 Te 0.26 ); Figure 4 (e) is the compression curve of the silver-based chalcogenide thermoelectric material (Ag 2 S 0.40 Se 0.34 Te 0.26 ); Figure 4 (f) is the bending curve of the silver-based chalcogenide thermoelectric material (Ag 2 S 0.40 Se 0.34 Te 0.26 ).

[0026] Figure 5 are the thermoelectric and mechanical properties of the silver-based chalcogenide thermoelectric material (Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 ) in an embodiment of the present invention. Among them, Figure 5 (a) is the electrical conductivity of the silver-based chalcogenide thermoelectric material (Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 ); Figure 5 (b) is the Seebeck coefficient of the silver-based chalcogenide thermoelectric material (Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 ); Figure 5 (c) is the thermal conductivity of the silver-based chalcogenide thermoelectric material (Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 ); Figure 5 (d) is the thermoelectric figure of merit ZT of the silver-based chalcogenide thermoelectric material (Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 ); Figure 5 (e) is the silver-based chalcogenide thermoelectric material (Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3)'s compression curve, Figure 5 (f) is the bending curve of the silver-based chalcogenide thermoelectric material (Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 ).

[0027] Figure 6 is the shape after bending of the silver-based chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ). Detailed implementation manners

[0028] In this article, a range represented by "from one numerical value to another numerical value" is a summary representation method to avoid listing all the numerical values in this range one by one in the specification. Therefore, the description of a specific numerical range covers any numerical value within this numerical range and the smaller numerical range defined by any numerical value within this numerical range, as if the arbitrary numerical value and the smaller numerical range are clearly written in the specification.

[0029] The following further elaborates the present invention in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the protection scope of the present invention. Improvements and adjustments made by those skilled in the art according to the present invention in actual applications still fall within the protection scope of the present invention.

[0030] The silver-based chalcogenide Ag 2 X (X = S, Se or Te) is a new type of thermoelectric material with a simple composition, a complex crystal structure and atomic arrangement at the same time, having an extremely low thermal conductivity and great potential. The thermoelectric performance and mechanical properties of the Ag 2 X-based compound have great room for improvement. α-Ag 2 S is a semiconductor material with intrinsic plasticity, and its deformation ability can be comparable to that of some metals. Similarly, as the silver chalcogenide compounds, Ag 2 Se, Ag 2 Te, although they do not show plasticity at room temperature, have good thermoelectric performance in the room temperature region and the medium temperature region. The applicant of the present invention found that Ag 2 X has a similar chemical composition, providing the possibility of alloying. The applicant of the present invention, through a large number of studies on solid solution and doping of binary compounds, found that multi-element solid solution can further improve and enhance the thermoelectric performance and mechanical properties of the silver-based thermoelectric material. The applicant of the present invention further studied the quaternary solid solution and obtained a quaternary material Ag 2-δ S x Se y Te z .

[0031] First, the silver-based chalcogenide thermoelectric material of the present invention will be analyzed and described below.

[0032] The present invention provides a silver-based chalcogenide thermoelectric material with a chemical general formula of Ag 2-δ S x Se y Te z , where δ = 0 to 0.05, x = 0.25 to 0.8, y = 0 to 0.5, z = 0.3 to 0.7, and x + y + z = 1.

[0033] This silver-based chalcogenide thermoelectric material is a cubic structure quaternary compound with a special body-centered cubic crystal structure. It has excellent plasticity and deformation ability while ensuring thermoelectric performance, and can be used for flexible and special-shaped thermoelectric power generation and refrigeration, providing new ideas and directions for the research of related thermoelectric devices. The silver-based chalcogenide thermoelectric material provided by the present invention did not crack in both the three-point bending test and the compression test: the maximum compression strain obtained under the test conditions was 85%, and the maximum bending strain was 35%, far superior to the existing silver sulfide-based inorganic thermoelectric materials.

[0034] In the components of the silver-based chalcogenide thermoelectric material of the present invention, there are three anion components with nearly equal atomic ratios. On the one hand, it realizes the maximization of entropy and inhibits the existence of intermediate phase compounds, enabling the material of the present invention's components to exist stably; on the other hand, the presence of Se and Te enhances the covalent component of the chemical bonds in the material, and greatly improves the thermoelectric performance relative to Ag 2 S. In addition, in the silver-based chalcogenide thermoelectric material of the present invention, the Ag content is not limited to 2, but a certain fluctuation is allowed. And the applicant of the present invention has found that if the Ag content is adjusted within the range of 2 to 1.95, the conductive characteristics of the silver-based chalcogenide thermoelectric material can be effectively optimized, and the thermoelectric performance can be further greatly improved.

[0035] Next, the preparation method of the silver-based chalcogenide thermoelectric material of the present invention will be analyzed and described.

[0036] The preparation method of the silver-based chalcogenide thermoelectric material in the present invention includes the following steps:

[0037] According to the chemical formula Ag 2-δ S x Se y Te z Weigh Ag, S, Se and Te elemental substances, mix them as the initial raw materials, and vacuum package them in a quartz tube;

[0038] The initial raw materials are subjected to high-temperature melting reaction and cooled to room temperature to obtain the silver-based chalcogenide thermoelectric material.

[0039] In the preparation method of the present invention, a dense ingot can be directly obtained after the initial raw materials are melted and annealed, without steps such as sintering, which simplifies and optimizes the preparation steps and processes, and saves costs. In the preparation method of the present invention, the steps and specific parameters of the preparation method are designed according to the specific components in the initial raw materials and the performance requirements of the thermoelectric material.

[0040] In some possible embodiments, the purity of the Ag element is 99.9% or more, the purity of the S element is 99.9% or more, the purity of the Se element is 99.9% or more, and the purity of the Te element is 99.9% or more.

[0041] In some possible embodiments, after the initial raw materials are loaded into a crucible, they are vacuum-sealed in a quartz tube.

[0042] In some possible embodiments, the crucible is a polycrystalline boron nitride crucible, and the vacuum sealing is carried out by plasma or a flame gun in an argon atmosphere glove box.

[0043] In some possible embodiments, the initial raw materials are sealed in a quartz tube, the internal pressure is evacuated to 0.1 - 10 Pa, and then it is sealed with a flame gun.

[0044] In some possible embodiments, the high-temperature melting reaction is carried out in a vertical furnace.

[0045] In some possible embodiments, the high-temperature melting reaction specifically includes the following steps: heating to 900 - 1100 °C within 24 hours, holding for 24 hours, cooling to 700 - 850 °C within 12 hours, holding for 15 - 20 hours, then cooling to 400 - 500 °C, holding for 72 hours, and finally cooling to room temperature at a rate of 100 - 150 °C / h.

[0046] The application of the silver-based chalcogenide thermoelectric material of the present invention is analyzed and described below.

[0047] The silver-based chalcogenide thermoelectric material provided by the present invention can be applied in conventional and special thermoelectric devices, and the thermoelectric devices include conventional, flexible, special-shaped, and micro thermoelectric power generation and thermoelectric refrigeration devices, such as wearable flexible thermoelectric devices, special-shaped thermoelectric generators, pipeline temperature sensors, etc.

[0048] The silver-based chalcogenide thermoelectric material provided by the present invention is suitable for thermoelectric power generation or thermoelectric refrigeration in the medium and low temperature regions; its good plasticity can be used for precision machining to prepare various thermoelectric devices with different shapes and sizes, which can effectively utilize low-density heat sources and achieve the purpose of energy conservation and emission reduction to a certain extent. This silver-based chalcogenide thermoelectric material has excellent thermoelectric material properties, can undergo plastic deformation at room temperature, and has an extremely low thermal conductivity.

[0049] The present invention will be further described in detail below in conjunction with specific embodiments and the accompanying drawings.

[0050] Example 1:

[0051] Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 (δ = 0, x = y = z = 1 / 3)

[0052] Weigh the elemental raw materials Ag, Te, Se, and S according to a molar ratio of 6:1:1:1, mix them in a polycrystalline boron nitride crucible, and then encapsulate them in a quartz tube. Heat to 1000 °C in 24 hours, hold for 24 hours, cool to 700 °C in 12 hours, hold for 20 hours, then cool to 500 °C, hold for 72 hours, and finally cool to room temperature at a rate of 120 °C / h to obtain a sample. Then perform cutting and testing.

[0053] As Figure 3 shown, the obtained Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 bulk material's thermoelectric performance measurement shows that in the measured temperature range (300 - 500K), this material has a moderate Seebeck coefficient and a moderate electrical conductivity. Moreover, this material has a low thermal conductivity: in the temperature range of 300 - 500K, its value < 1.3W m -1 K -1 . At the same time, it has good plasticity at room temperature. Figure 6 is the shape of the silver-based chalcogenide thermoelectric material (Ag 2 S 1 / 3 Se 1 / 3 Te 1 / 3 ) after bending.

[0054] Example 2:

[0055] Ag 2 S 0.40 Se 0.34 Te 0.26 (δ = 0, x = 0.40, y = 0.34, z = 0.26)

[0056] Weigh the elemental raw materials Ag, Te, Se, and S according to a molar ratio of 1:0.40:0.34:0.26, mix them in a polycrystalline boron nitride crucible, and then encapsulate them in a quartz tube. Heat to 1100 °C in 24 hours, hold for 24 hours, cool to 700 °C in 12 hours, hold for 15 hours, then cool to 400 °C, hold for 72 hours, and finally cool to room temperature at a rate of 100 °C / h to obtain a sample. Then perform cutting and testing.

[0057] As shown Figure 4 in the figure, the obtained Ag 2 S 0.40 Se 0.34 Te 0.26 bulk material's thermoelectric property measurement shows that within the measured temperature range (300 - 500K), this material has a moderate Seebeck coefficient and a moderate electrical conductivity. Moreover, this material has a low thermal conductivity: within the temperature range of 300 - 500K, its value < 1.4Wm -1 K -1 . Meanwhile, it has good plasticity at room temperature.

[0058] Example 3:

[0059] Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 (δ = 0.02, x = y = z = 1 / 3)

[0060] Weigh the elemental raw materials Ag, Te, Se and S according to the molar ratio of 5.94:1:1:1, mix them in a polycrystalline boron nitride crucible, and then encapsulate them in a quartz tube. Heat it to 1100°C in 24 hours, keep it warm for 24 hours, cool it to 800°C in 12 hours, keep it warm for 15 hours, then cool it to 500°C, keep it warm for 72 hours, and finally cool it to room temperature at a rate of 150°C / h to obtain the sample. Then cut and test it.

[0061] As shown Figure 5 in the figure, the obtained Ag 1.98 S 1 / 3 Se 1 / 3 Te 1 / 3 bulk material's thermoelectric property measurement shows that within the measured temperature range (300 - 500K), this material has a moderate Seebeck coefficient and a moderate electrical conductivity. Moreover, this material has a low thermal conductivity: within the temperature range of 300 - 500K, its value < 0.52W m -1 K -1 ; its thermoelectric figure of merit (zT) reaches 0.32 at room temperature and 0.63 at 460K. Meanwhile, it has good plasticity at room temperature.

[0062] What is disclosed above is only the preferred embodiments of the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, according to the content of this specification, many modifications and changes can be made. This specification selects and specifically describes these embodiments to better explain the principle and practical application of the present invention, so that those skilled in the art can make good use of the present invention. The present invention is only limited by the claims and their full scope and equivalents.

[0063] Under the teachings of the present invention and the above embodiments, those skilled in the art can easily foresee that the present invention can be implemented by each of the raw materials or their equivalent substitutes, each processing method or their equivalent substitutes listed or exemplified in the present invention, and the upper and lower limit values and interval values of the parameters of each raw material and processing method can also implement the present invention. Embodiments are not enumerated one by one here.

Claims

1. A preparation method of a silver-based chalcogenide thermoelectric material, characterized in that, The chemical formula of the silver chalcogenide thermoelectric material is Ag 2-d S x Se y Te z , where d = 0 to 0.05, x = 0.25 to 0.8, y = 0 to 0.5, z = 0.3 to 0.7, and x + y + z = 1. The thermoelectric material is an n-type thermoelectric material with a cubic crystal structure; the preparation method of the silver-based chalcogenide thermoelectric material includes: According to the chemical formula of the silver chalcogenide thermoelectric material Ag 2-d S x Se y Te z Weigh the Ag, S, Se and Te elemental substances, mix them as the initial raw materials, and vacuum package them in a quartz tube; performing a high-temperature melting reaction on the initial raw materials, and cooling to room temperature to obtain the silver-based chalcogenide thermoelectric material; wherein, the high-temperature melting reaction specifically includes the following steps: heating to 900 - 1100 °C within 24 hours, holding for 24 hours, cooling to 700 - 850 °C within 12 hours, holding for 15 - 20 hours, then cooling to 400 - 500 °C, holding for 72 hours, and finally cooling to room temperature at a rate of 100 - 150 °C / h.

2. The preparation method of the silver-based chalcogenide thermoelectric material according to claim 1, characterized in that, the purity of the Ag element is 99.9% or above, the purity of the S element is 99.9% or above, the purity of the Se element is 99.9% or above, and the purity of the Te element is 99.9% or above.

3. The preparation method of the silver-based chalcogenide thermoelectric material according to claim 1, characterized in that, the initial raw materials are loaded into a crucible and then vacuum-sealed in a quartz tube.

4. The preparation method of the silver-based chalcogenide thermoelectric material according to claim 3, characterized in that, the crucible is a polycrystalline boron nitride crucible, and the vacuum sealing is performed by plasma or a flame gun in an argon atmosphere glove box.

5. The preparation method of the silver-based chalcogenide thermoelectric material according to claim 3, characterized in that, when the initial raw materials are sealed in the quartz tube, the internal pressure is evacuated to 0.1 - 10 Pa.

6. The preparation method of the silver-based chalcogenide thermoelectric material according to claim 1, characterized in that, the high-temperature melting reaction is carried out in a vertical furnace.

7. The application of the silver-based chalcogenide thermoelectric material prepared according to any one of claims 1 - 6 in thermoelectric power generation, thermoelectric refrigeration, and flexible electronics.

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