Highly preferred orientation CuAgSe material, and preparation method and application thereof

Abstract

The application relates to a high-preference orientation CuAgSe material and a preparation method and application thereof, and the preparation method is as follows: under an inert atmosphere, Cu, Ag and Se elements are placed in a sealed container and vacuumized to obtain a vacuum material; the vacuum material is quenched in a high-temperature molten state, and a cast ingot is obtained after cooling; the cast ingot is ground into powder, placed in a pointed container and vacuum-sealed, and secondary melting-annealing treatment is carried out in a high-temperature state, and a pointed columnar material is obtained after cooling; the pointed columnar material is placed in a pointed container again, vacuum-sealed, and crystal growth is carried out through an optical floating zone method, and a pointed columnar cast ingot, namely the CuAgSe material, is obtained after cooling, and the preparation is completed. Compared with the prior art, the CuAgSe material prepared by the application is a polycrystalline layered material mainly in an orthogonal phase, meets the requirement of thermal conductivity and electrical conductivity decoupling, and has important practical significance for preparing a crystal with good preference orientation and development of transverse thermoelectric effect for a similar system.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of thermoelectric materials, in particular to a high-preference orientation CuAgSe material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of global economy and technology, the consumption of non-renewable fossil energy grows exponentially. Scientists predict that global oil resources will be exhausted in 2050, and other fossil energy will be exhausted at the latest in 2100, so the development and utilization of new energy are imminent. In addition to solar energy, wind energy, water energy and the like, the huge energy contained in heat energy has also attracted great enthusiasm of scientists, such as indoor and outdoor temperature difference, waste heat of factories, exhaust emission of automobiles and the like. The heat energy-electricity conversion function of thermoelectric materials is the most effective way to realize the utilization of heat energy. Thermoelectric materials realize the conversion of heat energy into electricity through micro carriers, and realize reliable and stable heat energy conversion without transmission components, noise and pollution. The breakthrough of thermoelectric materials will be another milestone in the utilization of new energy.

[0003] In 1821, the German scientist Seebeck discovered the Seebeck effect, and in 1834, the French scientist Peltier discovered the inverse effect of the Seebeck effect, the Peltier effect, which are two basic theories of thermoelectric materials. The Seebeck effect is the effect that a temperature difference exists between the two ends of a conductor to generate an electric potential, and the Peltier effect is the phenomenon that a temperature difference is generated in a conductor to generate heat. The conversion efficiency is characterized by the thermoelectric figure of merit ZT, ZT = S 2 σT / κ, wherein S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the total thermal conductivity. The three physical parameters of the Seebeck coefficient, the electrical conductivity σ and the thermal conductivity κ which determine the thermoelectric figure of merit are interrelated, and it is difficult to significantly improve the thermoelectric figure of merit by independently adjusting a certain parameter, which is the main reason why the ZT value of the material system has rarely broken through 2 so far. SUMMARY

[0004] The purpose of the present application is to overcome the defects of the prior art and provide a high-preference orientation CuAgSe material and a preparation method and application thereof. The prepared CuAgSe material is a polycrystalline layered material mainly in the orthorhombic phase, meets the requirements of decoupling of thermal conductivity and electrical conductivity, and has important practical significance for preparing crystals with good preference orientation and developing transverse thermoelectric effect for similar systems.

[0005] The purpose of the present application can be achieved by the following technical scheme:

[0006] One of the technical schemes of the present application is to provide a preparation method of a high-preference orientation CuAgSe material, comprising the following steps:

[0007] (1) Vacuum sealing: placing copper (Cu), silver (Ag) and selenium (Se) elements in a sealed container under inert atmosphere and vacuumizing to obtain a vacuum material;

[0008] (2) Quenching treatment: quenching the vacuum material in a high-temperature molten state, and obtaining an ingot after cooling;

[0009] (3) Secondary melting-annealing treatment: grinding the ingot into powder, placing it in a sharp container and vacuum sealing, and performing secondary melting-annealing treatment under high temperature, and obtaining a sharp columnar material after cooling;

[0010] (4) Optical floating zone method crystal growth: placing the sharp columnar material into a sharp container again, vacuum sealing, and performing crystal growth by optical floating zone method, and obtaining a sharp columnar ingot, i.e. CuAgSe material, after cooling.

[0011] Further, in step (1), the molar ratio of Cu, Ag and Se elements is (0.8-1.2):(0.8-1.2):1. Further, it is (0.9-1.1):(0.9-1.1):1. Further preferably, it is 1:1:1.

[0012] Further, in step (1), the purity of Cu, Ag and Se elements is greater than or equal to 99.99%.

[0013] Further, in step (1), the specific process of vacuum sealing is as follows: under inert atmosphere, Cu, Ag and Se elements are poured into a crucible, and the crucible is placed in a glass tube, Se particles are placed in the glass tube outside the crucible, the glass tube is sealed, the glass tube filled with inert atmosphere is connected to a vacuum tube head, and the cycle of air exhaust and air filling is performed 1-5 times, the gas is washed, the vacuum is extracted to less than 3 Pa, and then the glass tube is sealed, the glass plug of the glass tube is heated at high temperature, the glass tube is softened, and the sample is vacuum sealed. The hydrogen-oxygen high-temperature small-gas-flame gun is used for sealing the vacuum sealing packaging place, only the sealing place is heated and sealed, the influence of heating on the sample is reduced, and the loss of Se particles during the packaging process is reduced.

[0014] Further, the mass ratio of Se particles to Se element is (50-100):1, and the purpose of placing Se particles in the glass tube outside the crucible is to create a saturated vapor environment of Se outside the crucible and minimize the volatilization of Se in the crucible.

[0015] Further, in step (1), the inert atmosphere includes argon atmosphere and nitrogen atmosphere.

[0016] Further, in step (2), the quenching treatment temperature is 1173-1573 K, the time is 15-30 h, and the heating rate is 0.5-1 K / min.

[0017] Furthermore, in step (3), the temperature of the secondary melting-annealing treatment is 973~1373 K, the time is 15~30h, and the heating rate is 0.8~1.5 K / min.

[0018] Furthermore, in step (4), the optical floating zone crystal growth is carried out in an optical floating zone furnace with a power of 10%~30%, a power growth rate of 1% / min~2% / min, and a crystal growth rate of 0.4~0.5 mm / h.

[0019] Furthermore, in steps (3) and (4), the pointed container used is a pointed carbon-coated glass tube, 100-200 mm long, with an outer diameter of 8-15 mm and an inner diameter of 2-8 mm. The purpose of the pointed glass tube is to determine the crystal orientation of the first crystal to solidify, thus ensuring that the subsequent crystals continue to grow along this orientation. The temperature is lowered first at the tip, causing the crystal to solidify first, thereby determining the initial crystal orientation and allowing the subsequent crystals to continue growing along this orientation. The purpose of carbon coating on the pointed glass tube is to prevent organic and inorganic substances on the glass tube from penetrating into the growing crystal through thermal diffusion during crystal growth; carbon coating effectively prevents the diffusion of impurities.

[0020] The second technical solution of the present invention is to provide a CuAgSe material with high preferred orientation, which is prepared by the above-mentioned preparation method.

[0021] Furthermore, the chemical formula of the CuAgSe material is CuAgSe.

[0022] The third technical solution of the present invention is to provide an application of a highly preferred orientation CuAgSe material in the field of thermoelectric materials.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention mainly grows crystals with preferred orientation, with the crystal planes mainly along the (052) direction and at a certain angle to the (001) crystal plane. Because CuAgSe is a layered material, the grown highly preferred orientation crystals can select directions with better electrical properties and lower thermal properties. The thermal and electrical properties of the crystals prepared by this method are decoupled in different directions. Therefore, the material can be well applied to Ettinghausen refrigeration devices. The CuAgSe material prepared by the present invention exhibits significant highly preferred orientation characteristics, which is consistent with the sample standards required for Ettinghausen refrigeration devices. By screening out directions with lower thermal properties and better electrical properties from these highly preferred orientation samples, a new scheme is provided for the material preparation of Ettinghausen refrigeration devices.

[0025] (2) This invention employs the optical floating zone method for crystal growth. Polycrystalline CuAgSe is placed in a carbon-coated pointed glass tube in the center of the cavity. Four halogen lamps surround the furnace body, and the light is concentrated and reflected by four hemispherical crystal faces onto a local area of ​​the glass tube containing the crystal for heating, covering a height of about 5 mm. The glass tube rotates clockwise to ensure uniform heating of the heated area. The halogen lamps move upward at a speed of 0.1~1 mm / h, slowly melting the crystal upward. The crystal leaving the melting zone gradually solidifies and slowly crystallizes upward. Since the second phase inside the crystal tends to melt in the liquid phase, most of the second phase is located at the top of the crystal, forming a mixed phase region, which can be effectively removed. Because the crystal faces of CuAgSe polycrystalline material produced by conventional melt-annealing are disordered, while the crystal grown by the optical floating zone method can ensure that the crystal grows in layers, thereby achieving high preferred orientation.

[0026] (3) The CuAgSe material prepared by the present invention has a more obvious preferred orientation, and can obtain crystals with decoupled thermal conductivity and electrical conductivity.

[0027] (4) The CuAgSe material prepared by this invention has better transverse thermoelectric effect performance compared with polycrystalline materials.

[0028] (5) The preparation process of the present invention is simple and easy to synthesize. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the crystal structure of the CuAgSe material prepared in this invention;

[0030] Figure 2 This is a schematic diagram of the growth of the CuAgSe material of the present invention in an optical floating zone furnace;

[0031] Figure 3 XRD comparison images of CuAgSe materials prepared in Examples 1 and 2 and Comparative Example 1;

[0032] Figure 4 The resistivity of CuAgSe materials prepared in Example 3 and Comparative Example 5 varies with temperature;

[0033] Figure 5 The resistivity change of CuAgSe materials prepared in Example 3 and Comparative Example 5 under a magnetic field;

[0034] Figure 6 The graph shows the Seebeck coefficient as a function of temperature for the CuAgSe materials prepared in Example 3 and Comparative Example 5.

[0035] Figure 7 This is a schematic diagram showing the change in thermal conductivity as a function of temperature for the CuAgSe materials prepared in Example 3 and Comparative Example 5. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. All other embodiments obtained by those skilled in the art based on the given embodiments without creative effort are within the scope of protection of this application.

[0037] Unless otherwise specified, the reagents, methods, instruments and equipment used in this invention are conventional reagents, methods, instruments and equipment in the art.

[0038] Example 1

[0039] This embodiment provides a method for preparing a CuAgSe material with high preferred orientation, including the following steps:

[0040] (1) Vacuum sealing

[0041] Five gs of Cu, Ag, and Se elements were prepared in a 1:1:1 molar ratio (Cu:Ag:Se) and poured into a clean 10 mm diameter graphite crucible in an argon atmosphere within a glove box. The graphite crucible was then placed inside a quartz tube, and 0.02 g of Se granules were placed inside the quartz tube outside the crucible. The mixture was then sealed. The quartz tube, filled with an inert atmosphere, was connected to a vacuum tube. The tube was evacuated and purged three times to purge the gas, and finally, a vacuum was applied to a pressure below 3 Pa before sealing the quartz tube. The quartz stopper was heated with a high-temperature oxyhydrogen flame torch to soften the quartz tube, allowing the sample to be vacuum-sealed, resulting in a vacuum-sealed quartz tube. The purity of the Cu, Ag, and Se elements was greater than or equal to 99.99%.

[0042] (2) Quenching treatment

[0043] The vacuum material quartz tube was placed in a muffle furnace and heated to 1373 K at a rate of 0.8 K / min. It was held in a molten liquid state at 1373 K for 20 h, and then quenched directly at 1373 K. After cooling, an ingot was obtained.

[0044] (3) Secondary melting-annealing treatment

[0045] After the ingot is ground into fine powder, it is placed in a carbon-coated pointed glass tube and vacuum sealed. Then it is placed in a muffle furnace and heated to 1173 K at a rate of 1 K / min. It is melted and held at 1173 K for 24 hours. The furnace is then cooled to room temperature to obtain a pointed columnar material.

[0046] (4) Optical floating zone crystal growth

[0047] The pointed columnar material was placed in a pointed carbon-coated glass tube, vacuum-sealed, and then placed in an optical floating zone furnace. It was grown at a power growth rate of 1.25% / min until reaching 21% power, and then crystallized at 21% power and a growth rate of 0.5 mm / h, followed by a 20-h cooling process. This yielded a pointed columnar ingot, i.e., CuAgSe material, and the preparation was complete. Its crystal structure is as follows... Figure 1 As shown, Se atoms are distributed in specific positions in the tetrahedral structure, including the centers of the top and bottom faces, as well as the vertices and edges. Cu atoms occupy the upper 1 / 4 of the edge positions, while Ag atoms are partially located in the same 1 / 4 edge positions, and the remaining Ag atoms form the structure at the center of the tetrahedron.

[0048] A schematic diagram of the optical floating zone crystal growth process is shown below. Figure 2 As shown, polycrystalline CuAgSe is placed in a carbon-coated pointed glass tube in the middle of the cavity. There are four halogen lamps around the furnace body. The light is concentrated and reflected by the four hemispherical crystal faces to heat the local area of ​​the glass tube containing the crystal, covering a height of about 5 mm. The glass tube rotates clockwise to ensure uniform heating of the heated area. The halogen lamps move upward at a speed of 0.1~1 mm / h, slowly melting the crystal upward. The crystal leaving the melting zone gradually solidifies and slowly crystallizes upward. The second phase inside the crystal tends to melt into the liquid phase, resulting in most of the second phase being at the top of the crystal, forming an impurity phase region that can be effectively removed.

[0049] The preparation process of the pointed carbon-coated glass tube is as follows: Quartz glass is placed in a horizontal tube furnace and heated to 1273 K. Argon gas carrying alcohol is then introduced into the horizontal tube furnace. The alcohol undergoes incomplete combustion at high temperature to produce elemental carbon. The elemental carbon is carried by the argon gas and deposited on the quartz glass tube. After 50 minutes of deposition, a pointed carbon-coated glass tube with a carbon film deposited on the inner wall of the quartz glass tube is obtained.

[0050] The CuAgSe block sample of this embodiment was subjected to XRD testing, and the test results are as follows: Figure 3 As shown. In this embodiment, it was observed that most of the characteristic peaks in the X-ray diffraction (XRD) pattern of the CuAgSe sample had weakened or disappeared, with only the sharp peak of the (052) crystal plane remaining. This phenomenon indicates that the relative abundance of the (052) crystal plane is relatively high, and the corresponding grain size is relatively large, thus preliminarily inferring that the sample has exhibited a certain degree of highly preferred orientation crystal structure.

[0051] Example 2

[0052] This embodiment provides a method for preparing a CuAgSe material with high preferred orientation, including the following steps:

[0053] (1) Vacuum sealing

[0054] Five gs of Cu, Ag, and Se elements were prepared in a 1:1:1 molar ratio (Cu:Ag:Se) and poured into a clean 10 mm diameter graphite crucible in an argon atmosphere within a glove box. The graphite crucible was then placed inside a quartz tube, and 0.02 g of Se granules were placed inside the quartz tube outside the crucible. The mixture was then sealed. The quartz tube, filled with an inert atmosphere, was connected to a vacuum tube. The tube was evacuated and purged three times to purge the gas, and finally, a vacuum was applied to a pressure below 3 Pa before sealing the quartz tube. The quartz stopper was heated with a high-temperature oxyhydrogen flame torch to soften the quartz tube, allowing the sample to be vacuum-sealed, resulting in a vacuum-sealed quartz tube. The purity of the Cu, Ag, and Se elements was greater than or equal to 99.99%.

[0055] (2) Quenching treatment

[0056] The vacuum material quartz tube was placed in a muffle furnace and heated to 1373 K at a rate of 0.8 K / min. It was held in a molten liquid state at 1373 K for 20 h, and then quenched directly at 1373 K. After cooling, an ingot was obtained.

[0057] (3) Secondary melting-annealing treatment

[0058] After the ingot is ground into fine powder, it is placed in a carbon-coated pointed glass tube and vacuum sealed. Then it is placed in a muffle furnace and heated to 1173 K at a rate of 1 K / min. It is melted and held at 1173 K for 24 hours. The furnace is then cooled to room temperature to obtain a pointed columnar material.

[0059] (4) Optical floating zone crystal growth

[0060] The pointed columnar material was placed in a pointed carbon-coated glass tube, vacuum-sealed, and then placed in an optical floating zone furnace. The tube was grown at a power growth rate of 1.25% / min until the power reached 21%, and then crystal growth was carried out at 21% power and a growth rate of 0.4 mm / h, followed by a cooling period of 20 h. This yielded a pointed columnar ingot, i.e., CuAgSe material, completing the preparation process.

[0061] The CuAgSe block sample of this embodiment was subjected to XRD testing, and the test results are as follows: Figure 3 As shown. The diffraction pattern of the CuAgSe sample in this embodiment is mainly characterized by a significant peak on the (052) crystal plane, while the intensity of other smaller diffraction peaks is relatively weakened. This result indicates that the highly preferred orientation of CuAgSe material on the (052) crystal plane was successfully achieved using this preparation method. This crystal plane was preferentially grown during crystal growth, thus becoming the dominant crystal plane of the material.

[0062] Example 3

[0063] This embodiment provides a method for preparing a CuAgSe material with high preferred orientation, including the following steps:

[0064] (1) Vacuum sealing

[0065] Five gs of Cu, Ag, and Se elements were prepared in a 1:1:1 molar ratio (Cu:Ag:Se) and poured into a clean 10 mm diameter graphite crucible in an argon atmosphere within a glove box. The graphite crucible was then placed inside a quartz tube, and 0.02 g of Se granules were placed inside the quartz tube outside the crucible. The mixture was then sealed. The quartz tube, filled with an inert atmosphere, was connected to a vacuum tube. The tube was evacuated and purged three times to purge the gas, and finally, a vacuum was applied to a pressure below 3 Pa before sealing the quartz tube. The quartz stopper was heated with a high-temperature oxyhydrogen flame torch to soften the quartz tube, allowing the sample to be vacuum-sealed, resulting in a vacuum-sealed quartz tube. The purity of the Cu, Ag, and Se elements was greater than or equal to 99.99%.

[0066] (2) Quenching treatment

[0067] The vacuum material quartz tube was placed in a muffle furnace and heated to 1373 K at a rate of 0.8 K / min. It was held in a molten liquid state at 1373 K for 20 h, and then quenched directly at 1373 K. After cooling, an ingot was obtained.

[0068] (3) Secondary melting-annealing treatment

[0069] After the ingot is ground into fine powder, it is placed in a carbon-coated pointed glass tube and vacuum sealed. Then it is placed in a muffle furnace and heated to 1173 K at a rate of 1 K / min. It is melted and held at 1173 K for 24 hours. The furnace is then cooled to room temperature to obtain a pointed columnar material.

[0070] (4) Optical floating zone crystal growth

[0071] The pointed columnar material was placed in a pointed carbon-coated glass tube, vacuum-sealed, and then placed in an optical floating zone furnace. The tube was grown at a power growth rate of 1.25% / min until the power reached 21%, and then crystal growth was carried out at 21% power and a growth rate of 0.45 mm / h, followed by a cooling period of 20 h. This yielded a pointed columnar ingot, i.e., CuAgSe material, completing the preparation process.

[0072] The CuAgSe block sample of this embodiment was subjected to XRD testing, and the test results are as follows: Figure 3 As shown. The diffraction pattern of the CuAgSe sample in this embodiment is mainly characterized by a significant peak on the (052) crystal plane, while the intensity of other smaller diffraction peaks is relatively weakened. This result indicates that the highly preferred orientation of CuAgSe material on the (052) crystal plane was successfully achieved using this preparation method. This crystal plane was preferentially grown during crystal growth, thus becoming the dominant crystal plane of the material.

[0073] Comparative Example 1

[0074] This embodiment provides a method for preparing a CuAgSe material with high preferred orientation, including the following steps:

[0075] (1) Vacuum sealing

[0076] Five gs of Cu, Ag, and Se elements were prepared in a 1:1:1 molar ratio (Cu:Ag:Se) and poured into a clean 10 mm diameter graphite crucible in an argon atmosphere within a glove box. The graphite crucible was then placed inside a quartz tube, and 0.02 g of Se granules were placed inside the quartz tube outside the crucible. The mixture was then sealed. The quartz tube, filled with an inert atmosphere, was connected to a vacuum tube. The tube was evacuated and purged three times to purge the gas, and finally, a vacuum was applied to a pressure below 3 Pa before sealing the quartz tube. The quartz stopper was heated with a high-temperature oxyhydrogen flame torch to soften the quartz tube, allowing the sample to be vacuum-sealed, resulting in a vacuum-sealed quartz tube. The purity of the Cu, Ag, and Se elements was greater than or equal to 99.99%.

[0077] (2) Quenching treatment

[0078] The vacuum material quartz tube was placed in a muffle furnace and heated to 1373 K at a rate of 0.8 K / min. It was held in a molten liquid state at 1373 K for 20 h, and then quenched directly at 1373 K. After cooling, an ingot was obtained.

[0079] (3) Secondary melting-annealing treatment

[0080] After the ingot is ground into fine powder, it is placed in a carbon-coated pointed glass tube and vacuum sealed. Then it is placed in a muffle furnace and heated to 1173 K at a rate of 1 K / min. It is melted and held at 1173 K for 24 hours. The furnace is then cooled to room temperature to obtain a pointed columnar material.

[0081] (4) Optical floating zone crystal growth

[0082] The pointed columnar material was placed in a pointed carbon-coated glass tube, vacuum-sealed, and then placed in an optical floating zone furnace. The tube was grown at a power growth rate of 1.25% / min until the power reached 21%, and then crystal growth was carried out at 21% power and a growth rate of 0.33 mm / h, followed by a cooling period of 20 h. This yielded a pointed columnar ingot, i.e., CuAgSe material, completing the preparation process.

[0083] The X-ray diffraction pattern of the sample prepared in this embodiment is as follows: Figure 3As shown, in this embodiment, most peaks appear, and the preferred orientation is not as obvious as that of the samples grown at 0.4 mm / h and 0.5 mm / h. Therefore, the growth rate of this embodiment represents the minimum limit of the growth rate. In summary, the analysis of the above embodiments shows that a growth rate range of 0.33 mm / h to 0.6 mm / h can effectively grow crystals with high preferred orientation.

[0084] Comparative Example 2

[0085] This embodiment provides a method for preparing a CuAgSe material with high preferred orientation, including the following steps:

[0086] (1) Vacuum sealing

[0087] Five gs of Cu, Ag, and Se elements were prepared in a 1:1:1 molar ratio (Cu:Ag:Se) and poured into a clean 10 mm diameter graphite crucible in an argon atmosphere within a glove box. The graphite crucible was then placed inside a quartz tube, and 0.02 g of Se granules were placed inside the quartz tube outside the crucible. The mixture was then sealed. The quartz tube, filled with an inert atmosphere, was connected to a vacuum tube. The tube was evacuated and purged three times to purge the gas, and finally, a vacuum was applied to a pressure below 3 Pa before sealing the quartz tube. The quartz stopper was heated with a high-temperature oxyhydrogen flame torch to soften the quartz tube, allowing the sample to be vacuum-sealed, resulting in a vacuum-sealed quartz tube. The purity of the Cu, Ag, and Se elements was greater than or equal to 99.99%.

[0088] (2) Quenching treatment

[0089] The vacuum material quartz tube was placed in a muffle furnace and heated to 1373 K at a rate of 0.8 K / min. It was held in a molten liquid state at 1373 K for 20 h, and then quenched directly at 1373 K. After cooling, an ingot was obtained.

[0090] (3) Secondary melting-annealing treatment

[0091] After the ingot is ground into fine powder, it is placed in a carbon-coated pointed glass tube and vacuum sealed. Then it is placed in a muffle furnace and heated to 1173 K at a rate of 1 K / min. It is melted and held at 1173 K for 24 hours. The furnace is then cooled to room temperature to obtain a pointed columnar material.

[0092] (4) Optical floating zone crystal growth

[0093] The pointed columnar material was placed in a pointed carbon-coated glass tube, vacuum-sealed, and then placed in an optical floating zone furnace. The tube was grown at a power growth rate of 1.25% / min until the power reached 21%, and then crystal growth was carried out at 21% power and a growth rate of 0.6 mm / h, followed by a cooling period of 20 h. This yielded a pointed columnar ingot, i.e., CuAgSe material, completing the preparation process.

[0094] The X-ray diffraction pattern of the CuAgSe material crystal grown in this embodiment is as follows: Figure 3 As shown, by comparing the phase composition of the crystals prepared at growth rates of 0.4 mm / h and 0.5 mm / h, it can be seen that the preferred orientation of the crystals grown in this example is not so obvious. The main peaks are (150), (160) and (052). These three peaks are not obviously from the same crystal system. Therefore, the growth rate of 0.5 mm / h is the limit growth rate for CuAgSe with high preferred orientation.

[0095] Comparative Example 3

[0096] This embodiment provides a method for preparing a CuAgSe material with high preferred orientation, including the following steps:

[0097] (1) Vacuum sealing

[0098] Five gs of Cu, Ag, and Se elements were prepared in a 1:1:1 molar ratio (Cu:Ag:Se) and poured into a clean 10 mm diameter graphite crucible in an argon atmosphere within a glove box. The graphite crucible was then placed inside a quartz tube, and 0.02 g of Se granules were placed inside the quartz tube outside the crucible. The mixture was then sealed. The quartz tube, filled with an inert atmosphere, was connected to a vacuum tube. The tube was evacuated and purged three times to purge the gas, and finally, a vacuum was applied to a pressure below 3 Pa before sealing the quartz tube. The quartz stopper was heated with a high-temperature oxyhydrogen flame torch to soften the quartz tube, allowing the sample to be vacuum-sealed, resulting in a vacuum-sealed quartz tube. The purity of the Cu, Ag, and Se elements was greater than or equal to 99.99%.

[0099] (2) Quenching treatment

[0100] The vacuum material quartz tube was placed in a muffle furnace and heated to 1373 K at a rate of 0.8 K / min. It was held in a molten liquid state at 1373 K for 20 h, and then quenched directly at 1373 K. After cooling, an ingot was obtained.

[0101] (3) Secondary melting-annealing treatment

[0102] After the ingot is ground into fine powder, it is placed in a carbon-coated pointed glass tube and vacuum sealed. Then it is placed in a muffle furnace and heated to 1173 K at a rate of 1 K / min. It is melted and held at 1173 K for 24 hours. The furnace is then cooled to room temperature to obtain a pointed columnar material.

[0103] (4) Optical floating zone crystal growth

[0104] The pointed columnar material was placed in a pointed carbon-coated glass tube, vacuum-sealed, and then placed in an optical floating zone furnace. The tube was grown at a power growth rate of 1.25% / min until the power reached 21%, and then crystal growth was carried out at 21% power and a growth rate of 5 mm / h, followed by a cooling process for 20 h. This yielded a pointed columnar ingot, i.e., CuAgSe material, completing the preparation process.

[0105] The CuAgSe block sample of this embodiment was subjected to XRD testing, and the test results are as follows: Figure 3 As shown. In this embodiment, the analyzed sample did not exhibit significant preferred orientation characteristics. X-ray diffraction patterns showed that its diffraction peaks were mainly similar to the typical peak positions of polycrystalline CuAgSe. In addition, characteristic peaks of the Cu2Se impurity phase were also observed. These results indicate that under the experimental conditions, the growth rate of CuAgSe crystals was not sufficient to induce the formation of a highly preferred orientation structure.

[0106] Based on the analysis of the above embodiments, it can be seen that a growth rate of 0.4 mm / h to 0.5 mm / h can effectively grow crystals with high preferred orientation.

[0107] Comparative Example 4

[0108] Compared to Example 1, most of the components are the same, except that Cu, Ag, and Se are replaced with Cu, Nickel (Ni), Ag, and Se, according to the chemical formula Cu 0.95 Ni 0.05 Cu was prepared by mixing AgSe in a molar ratio of 0.95:0.05:1:1. 0.95 Ni 0.05 The X-ray diffraction pattern data of the sample made from AgSe material are as follows: Figure 3 As shown, all grown samples exhibit a CuSe second phase. If the prepared sample contains a CuSe second phase, the material's properties cannot be qualitatively analyzed, and the change in properties cannot avoid the involvement of the second phase. At the same time, the presence of the second phase also increases the number of defects in the grown crystal structure. However, during the optical floating zone method, CuSe tends to melt in the molten liquid phase, that is, it condenses at the end of the sample. This can be removed to eliminate the presence of the second phase in the crystal.

[0109] Comparative Example 5

[0110] Cu, Ag, and Se powders were mixed in a molar ratio of 1:1:1 (CuAgSe), weighed, and placed in a quartz glass tube. The tube was then evacuated to less than 3 Pa and sealed. It was placed in a muffle furnace and heated to 673 K at a rate of 20 K / h, then to 1073 K at a rate of 50 K / h and held at this temperature for 20 hours. Finally, it was cooled to room temperature at a rate of 100 K / h. The resulting ingot was ground into powder and then cold-pressed to prepare a block sample, CuAgSe. The performance data of the sample are as follows: Figures 4-7 As shown.

[0111] Figures 4-7 The results are the performance test results of the CuAgSe materials prepared in Example 3 and Comparative Example 5. Figure 4 and 5 It can be seen that the resistivity (ρ) of the CuAgSe material prepared in Example 3 at low temperature is... xx Both are lower than the CuAgSe material prepared in Comparative Example 5, ρ xx Regarding the temperature change, it is at least three orders of magnitude lower, ρ xx The change in magnetic field at 300 K is also at least two orders of magnitude lower. ρ xx The resistivity increases with increasing temperature, plateauing at 75 K because the crystal begins to transform from a tetragonal phase to an orthorhombic phase. Under a magnetic field, the resistivity gradually increases with increasing magnetic field, indicating that CuAgSe possesses an inherent magnetoresistance effect. Figure 6 It can be seen that the Seebeck coefficient increases with increasing temperature, but after 50 K, the Seebeck coefficient of the CuAgSe material prepared in Example 3 is greater than that of the CuAgSe material prepared in Comparative Example 5. The Seebeck coefficient at 300 K can reach -107 S / m. Figure 7 It can be seen that the thermal conductivity of the CuAgSe material prepared in Example 3 is higher than that of the CuAgSe material prepared in Comparative Example 5 in the temperature range of 5 K to 67 K. This is because the CuAgSe material prepared in Example 3 has a larger crystal grain size, fewer grain boundaries, and a longer phonon relaxation time, resulting in higher thermal conductivity at low temperatures. In the temperature range of 67 K to 300 K, the overall thermal conductivity is lower than that of the CuAgSe material prepared in Comparative Example 5 because the crystal structure gradually transforms from a tetragonal phase to a cubic phase after 67 K. The average thermal conductivity is also lower than that of Ishiwata across the entire temperature range.

[0112] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a CuAgSe material with high preferred orientation, characterized in that, Includes the following steps: (1) Vacuum sealing: Cu, Ag and Se elements are placed in a sealed container under an inert atmosphere and a vacuum is drawn to obtain vacuum material; (2) Quenching treatment: The vacuum material is quenched in a high-temperature molten state and then cooled to obtain an ingot; (3) Secondary melting-annealing treatment: After grinding the ingot into powder, it is placed in a pointed container and vacuum sealed. Secondary melting-annealing treatment is carried out at high temperature. After cooling, a pointed columnar material is obtained. (4) Optical floating zone method for crystal growth: The pointed columnar material is placed back into the pointed container, vacuum sealed, and crystal growth is carried out by optical floating zone method. After cooling, a pointed columnar ingot is obtained, namely CuAgSe material. The preparation is completed. The chemical formula of the CuAgSe material is CuAgSe. In step (4), the optical floating zone crystal growth is carried out in an optical floating zone furnace with a power of 10%~30% and a crystal growth rate of 0.4~0.5 mm / h.

2. The method for preparing a highly preferred orientation CuAgSe material according to claim 1, characterized in that, In step (1), the molar ratio of Cu, Ag and Se is (0.8~1.2):(0.8~1.2):

1.

3. The method for preparing a highly preferred orientation CuAgSe material according to claim 1, characterized in that, In step (1), the specific process of vacuum sealing is as follows: Under an inert atmosphere, Cu, Ag and Se elements are poured into a crucible and placed inside a glass tube. Se particles are placed inside the glass tube outside the crucible. The glass tube is sealed and the glass tube filled with inert gas is connected to the vacuum tube head. The gas is pumped and purged 1 to 5 times, the gas is washed, and the glass tube is sealed after being evacuated to less than 3 Pa. The glass stopper of the glass tube is heated at high temperature to soften the glass tube and vacuum seal the sample.

4. The method for preparing a highly preferred orientation CuAgSe material according to claim 1, characterized in that, In step (1), the inert atmosphere includes an argon atmosphere and a nitrogen atmosphere.

5. The method for preparing a highly preferred orientation CuAgSe material according to claim 1, characterized in that, In step (2), the quenching temperature is 1173~1573 K and the heating rate is 0.5~1 K / min.

6. The method for preparing a highly preferred orientation CuAgSe material according to claim 1, characterized in that, In step (3), the temperature of the secondary melting-annealing treatment is 973~1373 K, and the heating rate is 0.8~1.5 K / min.

7. The method for preparing a highly preferred orientation CuAgSe material according to claim 1, characterized in that, In step (4), the power growth rate is 1% / min to 2% / min.

8. A highly preferred orientation CuAgSe material, which is prepared by the preparation method described in any one of claims 1 to 7.

9. The application of the highly preferred orientation CuAgSe material as described in claim 8 in the field of thermoelectric materials.

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