Preparation method of sintering temperature regulated SrAgSb Zintl phase thermoelectric material

Abstract

The application relates to a sintering temperature regulated SrAgSb Zintl phase thermoelectric material and a preparation method and application thereof, and belongs to the technical field of thermoelectric functional material preparation. The method comprises the following steps: under an inert atmosphere, Sr, Ag and Sb are proportioned according to a stoichiometric ratio, wherein the Sr raw material is purified through arc melting first; the prepared raw material is placed in a quartz tube for sealing, and high-temperature solid-phase reaction is carried out at 1223 K for 72 h; after cooling, the raw material is ground in the inert atmosphere to obtain SrAgSb precursor powder; the precursor powder is loaded into a graphite mold, and is subjected to discharge plasma sintering at 500-700 DEG C under a pressure of 70 MPa for 2 min to obtain a bulk thermoelectric material with hexagonal ZrBeSi type SrAgSb as a main phase and a relative density not less than 95%. The application can improve the comprehensive performance of the SrAgSb-based thermoelectric material without complex doping or multi-component alloying, the process window is clear and the repeatability is good, and the application is suitable for medium and high temperature thermoelectric power generation, industrial waste heat recovery and solid-state thermoelectric conversion devices.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric functional materials and inorganic semiconductor material preparation technology. Specifically, it relates to a preparation method for SrAgSb Zintl phase thermoelectric materials by controlling the crystal structure, grain size, defect state, electrical transport properties and thermal transport properties through discharge plasma sintering temperature, as well as the SrAgSb bulk thermoelectric materials prepared by this method and their applications. Background Technology

[0002] Thermoelectric materials enable the direct conversion between thermal energy and electrical energy, and have significant application value in fields such as industrial waste heat recovery, automotive exhaust waste heat utilization, distributed energy supply, solid-state refrigeration, and wearable electronic devices. Thermoelectric conversion efficiency is typically expressed as the dimensionless thermoelectric figure of merit. zT express, zT = S ² σT / k ,in S For Seebeck coefficients, s For electrical conductivity, T Absolute temperature k The total thermal conductivity is denoted as . High-performance thermoelectric materials need to simultaneously possess a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. However, electrical conductivity, Seebeck coefficient, and electronic thermal conductivity are all closely coupled with carrier concentration; improving one parameter often sacrifices another. Therefore, achieving synergistic optimization of electrical and thermal transport is a key issue in the research and industrial application of thermoelectric materials.

[0003] Zintl phase compounds have attracted widespread attention due to their structural features of coexisting ionic and covalent bonds, complex unit cells, tunable carrier concentration, and low lattice thermal conductivity. SrAgSb is a typical 1-1-1 type ZrBeSi Zintl phase compound, usually belonging to the P63 / mmc space group. Its crystal structure consists of alternating stacking of Ag-Sb honeycomb covalent layers and Sr cation layers along the c-axis. The Ag-Sb covalent layers provide relatively continuous carrier transport channels, while the complexity of the Sr cation layers and the layered structure enhances phonon scattering, making this material promising for applications in medium- and high-temperature thermoelectric energy conversion.

[0004] Optimization of the performance of existing SrAgSb-based thermoelectric materials largely relies on compositional modulation, carrier concentration adjustment, or doping modification. While these methods can improve some electrical transport properties, they increase process complexity and compositional uncertainty, and may introduce additional impurities or local compositional fluctuations. Furthermore, the thermoelectric transport properties of SrAgSb are extremely sensitive to the fabrication process, especially during spark plasma sintering, where the sintering temperature significantly affects the sample's densification, crystal structure order, grain size, grain boundary density, defect concentration, carrier mobility, and phonon mean free path. At lower sintering temperatures, the sample may retain more grain boundaries and residual defects, which is beneficial for phonon scattering, but may also lead to insufficient crystal quality or an excessively high contribution of electronic thermal conductivity. At higher sintering temperatures, grain growth and increased lattice rigidity weaken the scattering of phonons by grain boundaries and may induce local elemental deviations or defect redistribution, thereby reducing carrier mobility. Therefore, it is necessary to establish a SrAgSb preparation method with sintering temperature as the core control variable, so as to achieve synergistic optimization of grain size, carrier transport and phonon transport without introducing complex doping elements. Summary of the Invention

[0005] The purpose of this invention is to address the problems of unclear process windows, complex doping and modification, and difficulty in synergistic optimization of electro-thermal transport in existing SrAgSb-based thermoelectric materials. This invention provides a SrAgSb Zintl phase thermoelectric material with sintering temperature control and its preparation method. This method obtains SrAgSb precursor powder through a high-temperature solid-state reaction and achieves bulk densification and microstructure control within a defined spark plasma sintering temperature window, thereby achieving a better balance between electrical and thermal transport properties.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a method for preparing the Zintl phase thermoelectric material SrAgSb, comprising the following steps: 1) Raw material pretreatment and batching: Granular Sr is melted and cast into blocks in an electric arc furnace to remove surface oxides; the purified Sr blocks, Ag granules or powder, and Sb granules or powder are batched in an inert atmosphere at a molar ratio of Sr:Ag:Sb=1:1:1. Preferably, the purity of Sr is not less than 99.5%, and the purity of Ag and Sb is not less than 99.9%. The batching and transfer process is carried out in a glove box with a water content and oxygen content of less than 1 ppm.

[0007] 2) High-temperature solid-state reaction: The prepared Sr, Ag and Sb are placed in a quartz tube or an equivalent heat-resistant encapsulation container, and the tube is vacuumed or sealed under an inert atmosphere; then the sealed sample is placed in a muffle furnace or tube furnace and held at 1223 K for 72 h. After the reaction is completed, it is naturally cooled to room temperature to obtain SrAgSb alloy block.

[0008] 3) Preparation of precursor powder: The obtained SrAgSb alloy block was ground in an inert atmosphere to obtain SrAgSb precursor powder with uniform composition.

[0009] 4) Spark plasma sintering: The SrAgSb precursor powder is loaded into a graphite mold and subjected to spark plasma sintering at a pressure of 70 MPa. The sintering temperature is 500-700 ℃ and the holding time is 2 min to obtain SrAgSb bulk thermoelectric material with a relative density of not less than 95%.

[0010] 5) Sintering temperature optimization: The sintering temperature is controlled at 560-600 ℃, preferably 580 ℃, so that the material achieves a comprehensive match between electrical conductivity, Seebeck coefficient, electronic thermal conductivity and lattice thermal conductivity, thereby obtaining a high thermoelectric figure of merit.

[0011] On the other hand, the present invention provides a bulk SrAgSb Zintl phase thermoelectric material prepared by the above method. The material is dominated by hexagonal ZrBeSi type SrAgSb with space group [space group number missing]. P 63 / mmc; Within the sintering temperature range of 500-700 ℃, the Rietveld structure refinement reliability factor of the obtained samples is... R w Less than 10%, GOF A value less than 2 indicates that the main crystal structure is stable. By adjusting the sintering temperature, the XRD-refined grain size of the material can be controlled from approximately 88.3 nm to approximately 142.6 nm, and the cell volume can vary within the range of approximately 167.904-168.479 ų.

[0012] Preferably, under discharge plasma sintering conditions of 580 °C, the XRD-refined grain size of the SrAgSb bulk thermoelectric material is approximately 107.5 nm, and the room temperature carrier concentration is approximately 1.282 × 10⁻⁶. 20 cm -3 Room temperature mobility is approximately 174 cm⁻¹ 2 ·V -1 ·s -1 The transverse wave velocity is approximately 2233.19 m / s, the longitudinal wave velocity is approximately 3887.41 m / s, the average sound velocity is approximately 2480.35 m / s, and the Debye temperature is approximately 115.1 K; the highest thermoelectric figure of merit is at approximately 773 K. zT It is approximately 0.55.

[0013] The present invention also provides the application of the above-mentioned SrAgSb Zintl phase bulk thermoelectric material in medium and high temperature thermoelectric power generation, industrial waste heat recovery, solid-state thermoelectric conversion devices, thermoelectric modules and micro energy supply devices.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention uses sintering temperature as the core control parameter, which can improve the overall thermoelectric performance of SrAgSb without complex doping or multi-component alloying, thus reducing the difficulty of composition design and process control.

[0015] 2) The high-temperature solid-state reaction combined with spark plasma sintering process defined in this invention can obtain SrAgSb bulk thermoelectric materials with a relative density of not less than 95%, and the main body of the sample maintains a hexagonal ZrBeSi type structure with good structural stability.

[0016] 3) This invention reveals and utilizes the coupled control effect of sintering temperature on grain size, lattice stress, defect state, carrier concentration, carrier mobility and phonon scattering to establish the correspondence between “process-structure-transport performance” of SrAgSb material.

[0017] 4) Under the preferred sintering conditions of 580 °C, the material achieves a good match between power factor and thermal conductivity, obtaining a power factor of approximately 0.55 at approximately 773 K. zT The value is significantly better than the overall performance at sintering temperatures that are too low or too high.

[0018] 5) The method of the present invention has a clear process window, good repeatability, and low equipment requirements. It is compatible with subsequent carrier concentration control, defect engineering or solid solution alloying strategies, and has the potential to further improve the performance of SrAgSb-based thermoelectric materials. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the preparation and performance optimization process of the SrAgSb thermoelectric material with sintering temperature control according to the present invention.

[0020] Figure 2 This is a schematic diagram of the SrAgSb crystal structure.

[0021] Figure 3 XRD patterns, lattice constants a, c, and cell volume V of SrAgSb samples sintered at different temperatures are shown.

[0022] Figure 4 The XRD patterns of SrAgSb samples at different sintering temperatures are fitted and the grain size variation obtained after refinement are shown.

[0023] Figure 5 Backscattered electron images and energy scattering spectra of samples sintered at 500 ℃, 580 ℃, 650 ℃ and 700 ℃ (excluding samples sintered at 600 ℃).

[0024] Figure 6Backscattered electron image and energy scattering spectrum elemental distribution of the sample sintered at 600 °C.

[0025] Figure 7 The graphs show the conductivity, Seebeck coefficient, power factor, room temperature carrier concentration, and mobility of SrAgSb samples at different sintering temperatures.

[0026] Figure 8 The total thermal conductivity, electronic thermal conductivity, lattice thermal conductivity, and thermoelectric figure of merit are plotted for SrAgSb samples sintered at different temperatures.

[0027] Figure 8 The total thermal conductivity, electronic thermal conductivity, lattice thermal conductivity, and thermoelectric figure of merit are plotted for SrAgSb samples sintered at different temperatures.

[0028] Figure 9 This work is compared with the thermoelectric figure of merit of some other representative works. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments. These embodiments are used to illustrate the technical solutions and effects of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the concept of the present invention, those skilled in the art can make conventional adjustments to the purity of raw materials, packaging methods, sintering mold dimensions, holding time, or testing methods.

[0030] I. General Preparation Process Granular Sr was melted and cast into blocks in an electric arc furnace to remove surface oxides for purification. The purified Sr blocks, Ag, and Sb were weighed according to a stoichiometric ratio of Sr:Ag:Sb = 1:1:1 and then placed into a quartz tube. All batching, transfer, and grinding operations were performed in a high-purity argon glove box. The water and oxygen content in the glove box was preferably both below 0.3 ppm.

[0031] A glass stopper or equivalent barrier structure was placed at the top of the quartz tube to reduce material splashing or migration during the reaction. After sealing the tube, the sample was placed in a muffle furnace and heated to 1223 K at a heating rate of 1 K / min, held at that temperature for 72 h, and then allowed to cool naturally to room temperature after the power was turned off to obtain SrAgSb alloy bulk material.

[0032] The obtained alloy block was ground into powder in a glove box, and the powder was placed into a graphite mold with a diameter of 10 mm. Spark plasma sintering (SPS) was then performed at 70 MPa for 2 min. Samples were prepared at 500℃, 580℃, 600℃, 650℃, and 700℃ by varying the SPS sintering temperature. The relative density of all samples was not less than 95% of the theoretical density.

[0033] II. Testing and Evaluation Methods XRD data of the sample powder were acquired using an X-ray diffractometer with Cu-Kα radiation source. The 2θ range was 10°–90° with a step size of 0.02°. The Rietveld method was used to refine the structure of the diffraction data, obtaining the lattice constant, cell volume, peak shape parameters, and refined XRD grain size. The reliability of the fit was evaluated using Rw and GOF.

[0034] The morphology of the polished cross-section was observed using scanning electron microscopy, and the elemental distribution was analyzed using energy dispersive spectroscopy. The conductivity, Seebeck coefficient, and power factor were measured in the range of 300–773 K using the four-probe method in a helium atmosphere. PF according to PF = S 2 s Calculations were performed. Room temperature carrier concentration and carrier mobility were obtained using Hall effect measurements.

[0035] thermal conductivity k according to k = D · Cp · r Calculation, where D Where is the thermal diffusivity, Cp For isobaric heat capacity, r Density. Electron thermal conductivity. k e According to the Wiedemann-Franz law k e = LσT Estimate the lattice thermal conductivity k L Depend on k L = k - k e Obtained. Thermoelectric figure of merit according to zT = S 2 σT / k Calculations were performed. The average sound velocity and Debye temperature were calculated through sound velocity measurements to analyze the effect of sintering temperature on lattice stiffness and phonon transport.

[0036] III. Example 1: Preferred sintered sample at 580℃ The raw materials were purified, batched, sealed in tubes for solid-state reaction, and ground into powder according to the general preparation process described above. The SrAgSb precursor powder was loaded into a graphite mold and sintered at 580 °C for 2 min under a pressure of 70 MPa to obtain SrAgSb bulk samples sintered at 580 °C.

[0037] XRD and Rietveld structure refinement results show that the sample retains a hexagonal ZrBeSi type SrAgSb main phase structure without significant structural phase transformation. Its lattice constant a is approximately 4.771 Å, lattice constant c is approximately 8.548 Å, cell volume is approximately 168.479 ų, and XRD-refined grain size is approximately 107.5 nm.

[0038] Hall tests showed that the carrier concentration of the sample at room temperature was approximately 1.282 × 10⁻⁶. 20 cm -3 The carrier mobility is approximately 174 cm⁻¹. 2 ·V -1 ·s -1 The sample achieves a good balance between conductivity and Seebeck coefficient, and exhibits excellent power factor performance within the test temperature range. Sound velocity test results show that the transverse wave velocity is approximately 2233.19 m / s, the longitudinal wave velocity is approximately 3887.41 m / s, the average sound velocity is approximately 2480.35 m / s, and the Debye temperature is approximately 115.1 K.

[0039] After considering both electrical and thermal transport properties, this sample achieves a maximum thermoelectric figure of merit of approximately 0.55 at approximately 773 K. zT The results show that a sintering temperature of 580 °C can achieve synergistic optimization among crystal quality, grain size, carrier mobility, power factor, and thermal conductivity, making it the preferred sintering condition for this invention.

[0040] IV. Example 2: Sintered sample at 500℃ Following the same high-temperature solid-state reaction and powder preparation process as in Example 1, the SrAgSb precursor powder was sintered at 500 °C for 2 min under a pressure of 70 MPa to obtain a sintered SrAgSb bulk sample at 500 °C.

[0041] The sample has a lattice constant a of approximately 4.769 Å, a lattice constant c of approximately 8.547 Å, a cell volume of approximately 168.386 ų, and an XRD-refined grain size of approximately 88.3 nm. Hall measurements yielded a room-temperature carrier concentration of approximately 1.197 × 10⁻⁶. 20 cm -3 The mobility is approximately 284 cm²·V. -1 ·s -1 .

[0042] The sample's smaller grain size and higher grain boundary density are beneficial for phonon scattering, but its relatively low Seebeck coefficient and large contribution from electronic thermal conductivity result in a comprehensive zT value below 580 °C, making it the preferred sample.

[0043] V. Example 3: Sintered sample at 600 °C Following the same process as in Example 1, the SrAgSb precursor powder was SPS sintered at 600 °C for 2 min under a pressure of 70 MPa to obtain a 600 °C sintered SrAgSb bulk sample.

[0044] The sample has a lattice constant a of approximately 4.767 Å, ​​a lattice constant c of approximately 8.538 Å, a cell volume of approximately 168.046 ų, and an XRD-refined grain size of approximately 119.8 nm. Hall measurements yielded a room-temperature carrier concentration of approximately 1.545 × 10⁻⁶. 20 cm -3 The mobility is approximately 91 cm²·V. -1 ·s -1 .

[0045] SEM / EDS observations revealed localized Sr and O enrichment regions, presumably corresponding to areas with minimal SrO or localized surface oxidation. This phenomenon suggests that increased sintering temperature may induce local defects or oxidation-related microregions, thereby increasing carrier concentration but decreasing mobility.

[0046] VI. Example 4: Sintered sample at 650 °C Following the same process as in Example 1, the SrAgSb precursor powder was SPS sintered at 650 °C for 2 min under a pressure of 70 MPa to obtain a 650 °C sintered SrAgSb bulk sample.

[0047] The sample has a lattice constant a of approximately 4.767 Å, ​​a lattice constant c of approximately 8.532 Å, a cell volume of approximately 167.904 ų, and an XRD-refined grain size of approximately 131.5 nm. Hall measurements yielded a room-temperature carrier concentration of approximately 1.598 × 10⁻⁶. 20 cm -3 The mobility is approximately 68 cm²·V. -1 ·s -1 .

[0048] As the sintering temperature increases, grain growth and structural ordering become more pronounced, but carrier mobility decreases significantly, and grain boundary phonon scattering weakens, which is not conducive to further improving the overall thermoelectric performance.

[0049] VII. Example 5: Sintered sample at 700 °C Following the same process as in Example 1, the SrAgSb precursor powder was SPS sintered at 700 °C for 2 min under a pressure of 70 MPa to obtain a 700 °C sintered SrAgSb bulk sample.

[0050] The sample has a lattice constant a of approximately 4.767 Å, ​​a lattice constant c of approximately 8.535 Å, a cell volume of approximately 167.984 ų, and an XRD-refined grain size of approximately 142.6 nm. Hall measurements yielded a room-temperature carrier concentration of approximately 1.576 × 10⁻⁶. 20 cm -3 The mobility is approximately 71 cm²·V. -1 ·s -1 .

[0051] Sound velocity tests showed that the sample had a transverse wave velocity of approximately 2400.00 m / s, a longitudinal wave velocity of approximately 4228.57 m / s, an average sound velocity of approximately 2668.36 m / s, and a Debye temperature of approximately 123.5 K. Compared with the low-temperature sintered sample, the high-temperature sintered sample exhibited enhanced lattice rigidity, larger grain size, and improved phonon propagation ability, but its advantage in lattice thermal conductivity was weakened. Therefore, the sample with the best overall thermoelectric performance did not exceed 580 °C.

[0052] VIII. Performance Data Summary Table 1 lists the lattice parameters and XRD-refined grain sizes of samples sintered at different temperatures. It can be seen that as the sintering temperature increases from 500 ℃ to 700 ℃, the overall cell volume decreases from 168.386 ų to 167.984 ų, while the XRD-refined grain size increases from 88.3 nm to 142.6 nm. This indicates that high-temperature sintering promotes lattice stress release, structural ordering, and grain growth.

[0053] Table 1. Lattice parameters and XRD-refined grain size of SrAgSb samples at different sintering temperatures (Note: The "Theoretical values" in the last row of Table 1 are theoretically calculated values ​​for characterizing the crystal structure of SrAgSb, used for comparison and reference). Table 2 lists the room temperature carrier concentration and mobility of samples at different sintering temperatures. Increasing the sintering temperature caused the carrier concentration to increase from 1.197 × 10⁻⁶ to 1.197 × 10⁻⁶. 20 cm -3 Increased to approximately 1.6 × 10 20 cm -3 At the same time, the mobility was reduced from 284 cm²·V -1 ·s -1 Significantly decreased to approximately 70 cm²·V -1 ·s -1 This indicates that sintering temperature significantly affects carrier transport by altering defect states and grain boundary characteristics.

[0054] Table 2. Room temperature carrier concentration and mobility of SrAgSb samples at different sintering temperatures. Table 3 lists the sound velocity, density, and Debye temperature of samples sintered at different temperatures. As the sintering temperature increases, the average sound velocity increases from 2368.63 m / s to 2668.36 m / s, and the Debye temperature increases from 110.9 K to 123.5 K, indicating that high-temperature sintering improves lattice rigidity and weakens grain boundary phonon scattering.

[0055] Table 3. Sound velocity, density, and Debye temperature of SrAgSb samples at different sintering temperatures. As can be seen from the above embodiments and test results, the sample sintered at 580 °C is not the sample with the highest single parameter, but rather the sample that achieves the best match between carrier concentration, mobility, grain size, phonon scattering, and thermal conductivity. While the sample sintered at 500 °C has a high mobility, its Seebeck coefficient is low and electronic thermal conductivity contributes significantly. Samples sintered at 600 °C and above, although having increased carrier concentration, show a significant decrease in mobility, and grain growth weakens phonon scattering. Therefore, the preferred sintering temperature of 580 °C yields the highest overall thermoelectric performance.

[0056] The above embodiments demonstrate that the present invention can enable SrAgSb Zintl phase thermoelectric materials to achieve performance levels close to those of compositionally optimized materials through simple and repeatable sintering temperature control, providing a process basis for further coupling and optimization with carrier concentration control, defect engineering, or solid solution alloying.

Claims

1. A method for preparing SrAgSbZintl phase thermoelectric materials with sintering temperature controlled, characterized in that, Includes the following steps: 1) Sr, Ag and Sb raw materials are placed in a quartz tube and sealed, and a high-temperature solid-state reaction is carried out to obtain SrAgSb alloy block; 2) The SrAgSb alloy block is ground in an inert atmosphere to obtain SrAgSb precursor powder; 3) The SrAgSb precursor powder was loaded into a graphite mold and subjected to discharge plasma sintering at a pressure of 70 MPa. The sintering temperature was 500-700 ℃ and the holding time was 2 min to obtain a dense bulk thermoelectric material with hexagonal ZrBeSi type SrAgSb as the main phase. Specifically, by adjusting the sintering temperature of the discharge plasma sintering, the XRD-refined grain size of the obtained SrAgSb bulk thermoelectric material is controlled to be 88-143 nm, and its electrical transport properties are matched with its thermal transport properties.

2. The preparation method according to claim 1, characterized in that, In step 1), the Sr raw material is melted into blocks by electric arc before being batched and the surface oxides are removed. The purity of Ag and Sb is not less than 99.99%, and the inert atmosphere is argon atmosphere.

3. The preparation method according to claim 1, characterized in that, Steps 1) through 3) were all carried out in a glove box or equivalent inert environment with water and oxygen content both below 1 ppm to reduce Sr oxidation and the formation of localized oxidation phases.

4. The preparation method according to claim 1, characterized in that, The high-temperature solid-phase reaction in step 1) is at a temperature of 1223 K, a holding time of 72 h, and a heating rate of 1 K / min.

5. The preparation method according to claim 1, characterized in that, The discharge plasma sintering pressure in step 3) is 70 MPa, and the holding time is 2 min.

6. The preparation method according to claim 1, characterized in that, The discharge plasma sintering temperature in step 3) is 560-600 ℃; preferably, the discharge plasma sintering temperature is 580 ℃.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The resulting SrAgSb bulk thermoelectric material has a relative density of not less than 95% and a crystal structure of space group 1. P The hexagonal ZrBeSi structure with 63 / mmc and the weighted residual factor refined by the Rietveld structure. R w Less than 10%, goodness of fit GOF Less than 2.

8. The preparation method according to claim 6, characterized in that, When the discharge plasma sintering temperature is 580 ℃, the XRD-refined grain size of the obtained SrAgSb bulk thermoelectric material is 100-115 nm, and the room temperature carrier concentration is 1.20 × 10⁻⁶. 20 -1.35×10 20 cm -3 The room temperature mobility is 150-190 cm⁻¹ 2 ·V -1 ·s -1 .

9. A SrAgSb Zintl phase bulk thermoelectric material, characterized in that, The SrAgSbZintl phase bulk thermoelectric material is prepared by the preparation method according to any one of claims 1 to 8, and has a thermoelectric figure of merit at approximately 773 K. zT Not less than 0.50, preferably about 0.

55.

10. The application of the SrAgSbZintl phase bulk thermoelectric material according to claim 9 in medium- and high-temperature thermoelectric power generation, industrial waste heat recovery, solid-state thermoelectric conversion devices or thermoelectric modules, wherein its operating temperature range includes 300-773 K.

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