CN113564714B - Anisotropic large size crystal and preparation method of AgCrSe2 - Google Patents

Abstract

The invention discloses anisotropyLarge size crystal and AgCrSe₂The preparation method of (1). Preparation of large-size AgCrSe with anisotropy₂The method for preparing the crystal comprises the following steps: (1) mixing AgCrSe₂Mixing the polycrystalline powder with a transmission medium, and putting the mixture into a sealable container for vacuumizing and sealing; (2) and (3) placing the sealed container in a horizontal double-temperature-zone heating environment for heating, so that one side, containing the mixture, of the container is located in a high-temperature zone, a vibration heating temperature curve is adopted in the heating process, and the heating time is 5-15 days. By adopting the method, not only can the AgCrSe be improved₂The size, thickness and quality of the crystal can obtain anisotropic large-size crystal, and is favorable for obtaining higher thermoelectric transport performance in special direction, for example, AgCrSe with size up to 7 mm and thickness up to 0.43 mm can be prepared by the method₂A crystalline material.

Description

Anisotropic large size crystal and preparation method of AgCrSe2

technical field

The invention belongs to the field of materials, and specifically relates to anisotropic large-sized crystals and a preparation method of AgCrSe ₂ .

Background technique

Thermoelectric material is an environmentally friendly "green" energy conversion material that can realize the direct mutual conversion of thermal energy and electrical energy. The limitation of traditional fossil energy utilization is of great significance.

The performance of thermoelectric materials is generally evaluated by the dimensionless thermoelectric figure of merit zT=S ² σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. High-performance thermoelectric materials require high Seebeck coefficients, high electrical conductivity, and low thermal conductivity. AgCrSe ₂ is a superionic conductor material with typical intercalation structure. Below the phase transition temperature T _c , Ag ions are ordered in the tetrahedral center composed of four Se atoms; above T _c , Ag ions are arranged in an orderly manner. The disorder is arranged at the center position of the equivalent Se atom tetrahedron, resulting in liquid-like behavior, which makes AgCrSe ₂ have the characteristics of "electronic crystal" and "phonon glass", and can obtain extremely low lattice thermal conductivity (~0.4 -0.5W·K ^-1 ·m ^-1 ). However, the origin of the extremely low lattice thermal conductivity is controversial. Some studies support it from disorder, and some support that the propagation of the shear wave acoustic branch is caused by the inhibition of ion diffusion. Analytical Interpretation of Subscattering and Ultrafast Transmission Electron Microscopy. Recent studies on layered single crystal materials have shown that the thermoelectric properties of layered materials along special directions can be significantly improved due to the bonding anisotropy, such as SnSe, Bi ₂ Te. Existing studies have shown that the electrical transport performance in the in-plane direction is found to be more than 100 times higher than that in the out-of-plane direction in the isostructural AgCrS ₂ single crystal material; and in the AgCrSe ₂ polycrystalline sample, it is found that the in-plane direction can obtain higher conductance. rate, while the thermal conductivity and Seebeck coefficient are basically consistent with the out-of-plane direction. Therefore, it is necessary to grow large-scale single crystals of _AgCrSe2 with a layered crystal structure in order to study the source of low thermal conductivity on the one hand, and obtain high in-plane thermoelectric properties on the other hand. Therefore, how to realize the growth of large-scale AgCrSe ₂ crystals with strong anisotropy is of great significance.

SUMMARY OF THE INVENTION

The present invention aims to solve one of the technical problems in the related art at least to a certain extent. Therefore, an object of the present invention is to propose a method for preparing anisotropic large-sized crystals and AgCrSe ₂ . The preparation method adopts oscillating heating temperature curve heating in the crystal growth process, which can not only obtain large-sized crystals with anisotropy, but also help to obtain high thermoelectric transport performance in special directions for thermoelectric materials.

This application is mainly based on the following findings of the inventors:

The inventors found that the study of fast ion movement and its effect on energy bands and phonons can explain the origin of thermal and electrical anisotropy from the atomic and even electronic levels, and promote the development of fast ion materials and even condensed matter physics. In the process of crystal growth, the energy required for step formation and diffusion is different. On this basis, a large number of macroscopic macroscales can be formed cyclically by controlling various process parameters in the growth process, such as the oscillation temperature curve, the gradient of high and low temperature regions, and the proportion of the transport medium. The crystal growth step promotes the continuous growth of large-sized crystals with strong anisotropic structure.

To this end, according to one aspect of the present invention, the present invention proposes a method for preparing anisotropic large-sized crystals. According to an embodiment of the present invention, the method employs oscillating heating temperature profile heating during crystal growth. For the existing technology, this method can not only improve the size, thickness and quality of the crystal material to obtain large-sized crystals with anisotropy, but also help to obtain high thermoelectric transport performance in special directions for thermoelectric materials.

In addition, the method for preparing anisotropic large-sized crystals according to the above embodiments of the present invention may also have the following additional technical features:

In some embodiments of the present invention, a horizontal dual-temperature zone vapor transport growth method is used in the crystal growth process, the dual-temperature zone includes a low temperature zone and a high temperature zone, at least one of the high temperature zone and the low temperature zone The oscillating heating temperature curve was used.

According to yet another aspect of the present invention, the present invention proposes a method for preparing large-sized AgCrSe ₂ crystals with anisotropy. According to an embodiment of the present invention, the method includes:

(1) Mix the AgCrSe ₂ polycrystalline powder and the transmission medium, and place the mixture in a sealable container for vacuuming and sealing;

(2) The sealed container is placed in a horizontal dual-temperature zone heating environment for heating, so that the side of the container containing the mixture is located in a high temperature zone, and the heating process adopts an oscillating heating temperature curve, and the heating time is 5 to 15 days.

The inventors found that the AgCrSe ₂ crystal material is a superionic conductor material with typical intercalation structure characteristics. During the crystal growth process, the step precipitation rate is lower than the drift rate. The temperature shock can increase the step deposition rate, that is, the atomic deposition rate. , and the crystal thickness can only be increased by increasing the deposition rate; and if the heating time is too short, the crystal growth cannot be guaranteed to proceed fully, and it is difficult to obtain the expected large-sized AgCrSe ₂ crystal. The method for preparing large-size AgCrSe ₂ crystals with anisotropy according to the above-mentioned embodiments of the present invention can utilize the difference in energy required for the formation and diffusion of steps during the growth of AgCrSe ₂ crystals, and control the oscillation temperature curve and the gradient of high and low temperature regions. Various process parameters in the growth process such as the proportion of the transport medium, cyclically form a large number of macroscopic crystal growth steps, and promote the continuous growth of AgCrSe ₂ crystals with strong anisotropic structure, which can not only improve the size, thickness and quality of AgCrSe ₂ crystals , to obtain large-sized crystals with anisotropy, and it is also beneficial to obtain high thermoelectric transport properties in special directions. Specifically, this method can be used to prepare AgCrSe ₂ crystal materials with a size of up to 7 mm and a thickness of up to 0.43 mm.

In addition, the method for preparing large-sized AgCrSe ₂ crystals with anisotropy according to the above embodiments of the present invention may also have the following additional technical features:

In some embodiments of the present invention, in step (1), the transmission medium is CrCl ₃ , and the mass-to-volume ratio of the transmission medium to the AgCrSe ₂ polycrystalline powder is 0.1-1 mg/cm ³ .

In some embodiments of the present invention, in step (1), the transmission medium is a mixture of CrCl ₃ and I ₂ , the mass ratio of CrCl ₃ to I ₂ is not less than 1, and the transmission medium and the AgCrSe ₂ are more The mass-volume ratio of the crystal powder is 0.15-1.2 mg/cm ³ .

In some embodiments of the present invention, in step (2), the dual temperature zone includes a high temperature zone and a low temperature zone, and at least one of the high temperature zone and the low temperature zone adopts an oscillating heating temperature curve.

In some embodiments of the present invention, step (2) is performed in a horizontal dual-temperature zone tube furnace, the sealable container is a quartz crucible, and the diameter of the quartz crucible is 10-30 mm.

In some embodiments of the present invention, the temperature range of the low temperature zone is 750-870°C, and the temperature of the high temperature zone is 25-70°C higher than the low temperature zone.

In some embodiments of the present invention, the oscillating heating temperature curve includes at least one oscillating cycle, and each of the oscillating cycles independently includes a low temperature plateau, a heating stage, a high temperature plateau and a cooling stage.

In some embodiments of the present invention, only the high temperature region or only the low temperature region adopts an oscillating heating temperature curve, the temperature oscillation amplitude of the oscillating heating temperature curve is 10 to 40°C, and each oscillation period is independently 1～40h.

In some embodiments of the present invention, both the high temperature zone and the low temperature zone adopt an oscillating heating temperature curve, and the temperature oscillation amplitudes of the oscillating heating temperature curves of the high temperature zone and the low temperature zone are independently 5-20 ℃, each shaking cycle is independently 1-40h.

In some embodiments of the present invention, the oscillating heating temperature curve includes a plurality of oscillating cycles, and in at least two consecutive oscillating cycles, the total duration of the next oscillating cycle is extended by 10~10 to the total duration of the previous oscillating cycle 50%.

In some embodiments of the present invention, the oscillating heating temperature curve includes a plurality of oscillating periods, and in at least two consecutive oscillating periods, the duration of the low temperature plateau, the heating period, the high temperature plateau and the cooling period of the next oscillation period are At least one of them is extended by 10-50% on the basis of the duration of the corresponding stage of the previous oscillation cycle.

In some embodiments of the present invention, the temperature gradient between the high temperature region and the low temperature region is 1˜10° C./cm.

In some embodiments of the present invention, the AgCrSe ₂ polycrystalline powder is prepared by the following steps: (i) mixing elemental particles Ag, Cr and Se according to the stoichiometric ratio of AgCrSe ₂ ; (ii) placing the mixture in a Ball milling in a ball mill and in an inert atmosphere; (iii) placing the ground fine powder in a sealable container and vacuuming and sealing; (iv) placing the sealed container in a high temperature environment for annealing treatment .

In some embodiments of the present invention, in step (i), the purity of the elemental particles is not lower than 4N.

In some embodiments of the present invention, in step (ii), the time of the ball milling treatment is 1-10 h.

In some embodiments of the present invention, in step (iii), directly evacuating to 10 ^-4 Pa and sealing; or, first evacuating and then filling with inert gas, after repeating 3 times, evacuating to 10 ^-1 Pa and sealing .

In some embodiments of the present invention, in step (iv), the temperature of the annealing treatment is 450˜800° C., and the time is 5˜50 h.

In some embodiments of the present invention, the AgCrSe ₂ polycrystalline powder is prepared by the following steps: (I) mixing elemental particles Ag, Cr and Se according to the stoichiometric ratio of AgCrSe ₂ ; (II) cooling the mixture Press into a block, and place the block raw material in a sealable container for vacuuming and sealing; (III) place the sealed container in a high temperature environment for annealing treatment.

In some embodiments of the present invention, in step (I), the purity of the elemental particles is not lower than 4N.

In some embodiments of the present invention, in step (II), directly evacuating to 10 ^-4 Pa and sealing; or, first evacuating and then filling inert gas, after repeating 3 times, evacuating to 10 ^-1 Pa and sealing .

In some embodiments of the present invention, in step (III), the temperature of the annealing treatment is 600˜900° C., and the time is 5˜50 h.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

1 is a flow chart of a method for preparing anisotropic large-size AgCrSe2 crystals according to an embodiment of the present invention;

2 is a schematic diagram of the growth of a gas phase transport crystal in a horizontal dual temperature zone according to an embodiment of the present invention, wherein the circle on the right is the heating body in the high temperature region, the circle on the left is the heating body in the low temperature region, and the dotted line is the transport mode of the transport medium.

Fig. 3 is the heating temperature curve diagram of crystal growth according to comparative example 1 of the present invention;

Fig. 4 is the AgCrSe ₂ wafer figure obtained according to the conventional gas phase transport method growth of Comparative Example 1 of the present invention;

Fig. 5 is the heating temperature curve diagram of crystal growth according to embodiment 1 of the present invention;

6 is a diagram of a grown AgCrSe ₂ wafer according to Example 1 of the present invention;

Fig. 7 is the heating temperature curve diagram of crystal growth according to embodiment 2 of the present invention;

8 is a diagram of a grown AgCrSe ₂ wafer according to Example 2 of the present invention;

9 is a comparison diagram of the XRD pattern of the AgCrSe ₂ wafer obtained by the ball-milled sample, the annealed sample and the AgCrSe 2 wafer obtained by oscillating and heating the annealed sample to realize crystal growth when preparing the AgCrSe ₂ polycrystalline sample according to an embodiment of the present invention and the standard card.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

It should be noted that the innovation of the present invention is the improvement of the heating method based on the vapor phase transport crystal growth, and the obtained oscillating temperature field has the following characteristics: periodically adjusting the saturated vapor pressure during the growth process to obtain continuous crystal growth conditions. Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any crystal growth method similar or equivalent to that described can be applied to the method of the present application. Methods and materials for preferred embodiments described herein are provided for illustrative purposes only.

According to one aspect of the present invention, the present invention proposes a method for preparing anisotropic large-sized crystals. According to an embodiment of the present invention, the method employs oscillating heating temperature profile heating during crystal growth. Preferably, a horizontal dual-temperature zone vapor transport growth method can be used in the crystal growth process, for example, a horizontal dual-temperature zone tube furnace can be used to perform horizontal dual-temperature zone heating; the dual-temperature zone includes a low-temperature zone and a high-temperature zone, wherein the high-temperature zone and At least one of the low temperature zones can adopt the oscillating heating temperature curve. For example, the oscillating heating in a single temperature zone can be adopted, and the heating process of only the high temperature zone or only the single temperature zone can adopt the oscillating heating temperature curve, or the two-temperature zone oscillating can be adopted. Heating, that is, the heating process of the high temperature zone and the low temperature zone adopts the oscillating heating temperature curve at the same time. The inventor found that the energy required for the formation and diffusion of steps in the crystal growth process is different. A large number of macroscopic crystal growth steps are formed, and the continuous growth of large-sized crystals with strong anisotropic structure is promoted. Therefore, for the prior art, the above-mentioned method for preparing anisotropic large-sized crystals of the present invention can not only improve the size, thickness and quality of crystal materials, and obtain large-sized crystals with anisotropy, but also facilitates thermoelectric materials. Obtain high thermoelectric transport performance in special directions.

According to yet another aspect of the present invention, the present invention proposes a method for preparing large-sized AgCrSe ₂ crystals with anisotropy. According to an embodiment of the present invention, as shown in FIG. 1 , the method includes:

S100: Mix the AgCrSe ₂ polycrystalline powder and the transmission medium, and place the mixture in a sealable container for vacuuming and sealing. The purity and thermoelectric properties of the final AgCrSe ₂ crystals can be further improved by vacuuming the mixture.

According to a specific embodiment of the present invention, the transmission medium may be CrCl ₃ , and the mass-to-volume ratio of CrCl ₃ to AgCrSe ₂ polycrystalline powder may be 0.1-1 mg/cm ³ , for example, 0.1 mg/cm ³ , 0.2 mg/cm ³ , 0.3mg/cm ³ , 0.4mg/cm ³ , 0.5mg/cm ³ , 0.6mg/cm ³ , 0.7mg/cm ³ , 0.8mg/cm ³ or 0.9mg/cm ³ , etc., the inventors found that if If the amount of transmission medium is too small, the growth of crystal nuclei cannot be achieved quickly, and if the amount of transmission medium is too much, it will lead to crystal nucleation and growth too fast, which will not only lead to the overall small size of crystals, but also the large number of crystals. There will be situations where the crystal quality is difficult to control. In the present invention, by controlling the addition amount of CrCl ₃ to the above range, it is more beneficial to obtain AgCrSe ₂ crystals with larger size and higher purity, so that the AgCrSe ₂ crystals have higher thermoelectric transport performance in specific directions.

According to yet another specific embodiment of the present invention, the transmission medium can be a mixture of CrCl ₃ and I ₂ , and the mass ratio of CrCl ₃ to I ₂ is not less than 1, for example, the mass ratio can be 1.5, 1.2 or 1, etc., CrCl ₃ and The mass volume ratio of the mixture of I ₂ to the AgCrSe ₂ polycrystalline powder is 0.15-1.2 mg/cm ³ , for example, 0.15 mg/cm ³ , 0.2 mg/cm ³ , 0.3 mg/cm ³ , 0.4 mg/cm ³ , 0.5 mg/cm ³ , 0.6 mg/cm ³ , 0.7 mg/cm ³ , 0.8 mg/cm ³ , 0.9 mg/cm ³ , 1 mg/cm ³ , 1.1 mg/cm ³ or 1.2 mg/cm ³ , etc. The inventor found that CrCl ₃ can be used to promote crystal growth, and I ₂ can be used to promote step deposition. If the total amount of CrCl ₃ and I ₂ is too small, the growth of the crystal nucleus cannot be quickly achieved, and if the total amount of the two is too much, It will lead to crystal nucleation and growth too fast, which will not only lead to the overall small size of the crystal, the number of which is too large, but also the situation that the crystal quality is difficult to control. In the present invention, by controlling CrCl ₃ and I ₂ to be in the above-mentioned ratio and addition amount range, it is more beneficial to obtain AgCrSe _{2 crystals with both larger size and thickness and higher purity, so that the AgCrSe 2 crystals} have relatively high purity in specific directions. High thermoelectric transport performance.

According to the embodiment of the present invention, the source of the AgCrSe ₂ polycrystalline powder in the present invention is not particularly limited, and those skilled in the art can choose according to actual needs. For example, the AgCrSe ₂ polycrystalline powder can be a commercially available product, or AgCrSe 2 polycrystalline powder can be used , Cr and Se were synthesized according to the stoichiometric ratio.

According to a specific embodiment of the present invention, AgCrSe ₂ polycrystalline powder can be prepared by the following steps: (i) mixing elemental particles Ag, Cr, and Se according to the stoichiometric ratio of AgCrSe ₂ , wherein the purity of each elemental particle may not be low In 4N, for example, it can be 99.999% or 99.9999%, etc.; (ii) the mixture is placed in a ball mill tank and ball-milled under an inert atmosphere, for example, the mixture can be put into a clean high-energy ball mill tank, filled with high Pure argon, ball mill for 1-10 hours, specifically 3h, 5h, 7h or 9h, etc.; (iii) place the ground fine powder in a sealable container and vacuumize and seal, for example, directly grind the The fine powder is put into a quartz tube, and the tube is sealed by vacuuming to 10 ^-4 Pa; it can also be vacuumed first and then filled with inert gas. After repeating 3 times, vacuumed to 10 ^-1 Pa and sealed. Further improve the purity of the obtained product; (iv) place the sealed container in a high temperature environment for annealing treatment, for example, put the loaded quartz tube into a muffle furnace, and anneal at 450-800 ° C for 5- 50 hours, specifically, the annealing temperature can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, etc., and the time can be 10h, 15h, 20h, 25h, 30h, 35h, 40h or 45h etc., the inventors found that the lower the annealing temperature, the longer the required annealing time. In the present invention, by controlling the above annealing conditions, both the annealing efficiency and the quality of the final AgCrSe ₂ polycrystalline sample can be guaranteed. Among them, Figure 9 is the XRD pattern of the ball-milled sample, the annealed sample and the AgCrSe ₂ wafer obtained by oscillating and heating the annealed sample to achieve crystal growth and the standard card. It can be seen from Figure 9 that the annealed AgCrSe ₂ polycrystalline sample and The fitting peaks (standard crystal structure) images of AgCrSe ₂ are completely consistent, indicating that AgCrSe ₂ polycrystalline samples were successfully synthesized after annealing treatment.

According to yet another specific embodiment of the present invention, AgCrSe ₂ polycrystalline powder can be prepared by adopting the following steps: (1) according to the stoichiometric ratio of AgCrSe ₂ , the elemental particles Ag, Cr, and Se are mixed, wherein the purity of each elemental particle can be different Below 4N, for example, it can be 99.999% or 99.9999%, etc.; (II) cold-press the mixture into a block, and place the block material in a sealable container for vacuuming and sealing, for example, the block material can be packed into Quartz tube, evacuate to 10 ^-4 Pa to seal the tube; you can also evacuate first and then fill with inert gas, after repeating 3 times, evacuate to 10 ^-1 Pa and seal the tube, which can further improve the obtained product Purity; (III) The sealed container is placed in a high temperature environment for annealing treatment, for example, the loaded quartz tube can be placed in a muffle furnace, and annealed at 600-900 ° C for 5-50 hours, specifically, The annealing temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C, etc., and the time can be 10h, 15h, 20h, 25h, 30h, 35h, 40h or 45h, etc., thus, both The annealing efficiency can be taken into account, and the quality of the final AgCrSe ₂ polycrystalline sample can be guaranteed.

S200: The sealed container is heated in a horizontal dual-temperature zone heating environment, so that the side of the container containing the mixture is located in the high temperature zone (as shown in Figure 2), and the heating process adopts an oscillating heating temperature curve, and the heating time is 5~ 15 days. The inventors found that the AgCrSe ₂ crystal material is a superionic conductor material with typical intercalation structure characteristics. During the crystal growth process, the step precipitation rate is lower than the drift rate. The temperature shock can increase the step deposition rate, that is, the atomic deposition rate. , and the crystal thickness can only be increased by increasing the deposition rate; and, if the heating time is too short, the crystal growth cannot be guaranteed to proceed fully, and it is difficult to obtain the expected large-sized AgCrSe ₂ crystal. Large-sized AgCrSe ₂ crystals were obtained.

According to a specific embodiment of the present invention, the crystal growth process can be performed in a horizontal dual temperature zone tube furnace, the horizontal dual temperature zone includes a high temperature zone and a low temperature zone, and the high and low temperature sections of the horizontal dual temperature zone tube furnace can be as long as Each is 30cm, referring to the direction of the high temperature zone and the low temperature zone shown in FIG. 2 , the temperature gradient between the high temperature zone and the low temperature zone can be 1-10°C/cm, for example, it can be 1-5°C/cm, 2°C/cm , 4°C/cm, 6°C/cm or 8°C/cm, etc., the sealable container can be a quartz crucible, and the diameter of the quartz crucible can be 10-30mm. The inventor found that if the temperature gradient between the high temperature region and the low temperature region is too small, the crystal growth is too slow; and if the temperature gradient between the high temperature region and the low temperature region is too large, the crystallization is too fast, and on the one hand there is too much nucleation. , it is difficult to grow up, on the other hand, one-dimensional whisker-like crystals will appear, and high-quality crystals can be obtained only in a reasonable gradient range; in the present invention, by controlling the temperature gradient between the two, it is more conducive to obtain both larger and larger The size and thickness, as well as the higher purity of the AgCrSe ₂ crystal, make the AgCrSe ₂ crystal have higher thermoelectric transport performance in a specific direction.

According to yet another specific embodiment of the present invention, at least one of the high temperature zone and the low temperature zone can adopt the oscillating heating temperature curve, and the inventors found that whether the single temperature zone oscillating heating or the double temperature zone oscillating heating is used, the increase The purpose of the deposition rate of the steps and the increase of the crystal thickness is that when the sum of the oscillation temperature amplitudes is similar, the effect of the oscillation in the single temperature zone and the oscillation in the dual temperature zone is similar. On this basis, the crystal growth can be further promoted by optimizing the oscillation temperature amplitude. , so that the crystal growth is more sufficient until all the raw materials are used.

According to another specific embodiment of the present invention, the temperature range of the low temperature zone may be 750-870°C, for example, it may be 770°C, 790°C, 810°C, 830°C, 850°C or 870°C, and the temperature of the high temperature zone may be higher than The low temperature zone is 25-70°C higher, for example, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C. If the temperature is too low, not only the reaction is slow, the crystal growth period is long, but also it is difficult to make the AgCrSe ₂ polycrystalline powder sample fully react; if the temperature is too high, the crystal growth will be too fast, and the product quality control will be more difficult. In the present invention, by controlling the low temperature region and the high temperature region to be the above temperature ranges, it is more beneficial to obtain AgCrSe ₂ crystals of expected size and higher purity, so that the AgCrSe ₂ crystals have higher thermoelectric transport performance in specific directions.

According to yet another specific embodiment of the present invention, the oscillating heating temperature curve may include at least one oscillating cycle, and each oscillating cycle independently includes a low-temperature plateau, a temperature-raising section, a high-temperature plateau, and a cooling-off section. For example, refer to FIG. 5 or FIG. 7 . The temperature can be raised to the first temperature in advance, after holding for a period of time at the first temperature, continue to heat up to the second temperature within the range of the oscillating temperature range, then hold the temperature at the second temperature for a period of time, and then cool down to the first temperature After that, it can continue to keep warm at the first temperature and enter the next oscillation cycle. Among them, in the process of temperature oscillation, from low temperature platform to high temperature platform is to realize the growth of crystals on the deposited steps and increase in size, the purpose of heat preservation is for step deposition and stability, and from high temperature platform to low temperature platform is to increase crystal steps. deposition. Preferably, the oscillation heating temperature curve may include multiple oscillation periods, for example, the number of oscillation periods may range from 1 to 100, such as 5, 10, 20, 50, 80 or 100, etc. The inventors found that , increasing the number of oscillation cycles can make the crystal growth more sufficient until all the raw materials are used, which can be more beneficial to increase the size of the final AgCrSe ₂ crystal.

According to another specific embodiment of the present invention, the crystal growth process can adopt the mode of single-temperature zone oscillating heating, that is, the oscillating heating temperature curve is only used in the high temperature region or only in the low temperature region, and the temperature oscillation of the oscillating heating temperature curve adopted at this time is The amplitude can be 10-40°C, such as 15°C, 20°C, 25°C, 30°C, 35°C or 40°C, etc., and each oscillation period can be independently 1-40h, such as 5h, 10h, 15h, 20h, 25h, 30h, 35h or 40h, etc., the inventors found that when using single-temperature zone oscillation heating, if the oscillation amplitude is too small, it will not accelerate the deposition of steps, and if the oscillation amplitude is too large, it will produce Excessive temperature gradient will lead to too fast crystal growth, and the quality of the obtained AgCrSe ₂ crystal will also decrease. Controlling the above temperature oscillation range is more conducive to increasing the deposition rate of crystal steps and improving the thickness and quality of crystals. It should be noted that the temperature oscillation amplitude in the present invention refers to the temperature difference between the high temperature plateau and the low temperature plateau in the oscillation heating temperature curve.

According to another specific embodiment of the present invention, the crystal growth process can adopt the mode of oscillation heating in dual temperature zones, that is, the high temperature zone and the low temperature zone can adopt the oscillation heating temperature curve at the same time, and the oscillation heating temperature curve of the high temperature zone and the low temperature zone can be The temperature oscillation range can be independently 5 to 20°C, such as 5°C, 8°C, 11°C, 14°C, 17°C, or 20°C, etc., and each oscillation period can be independently 1 to 40h, for example, it can be It is 5h, 10h, 15h, 20h, 25h, 30h, 35h or 40h, etc. The inventor found that when using dual-temperature zone vibration heating, if the sum of the vibration amplitudes of the high temperature zone and the low temperature zone is too small, it will not accelerate the step deposition. However, if the sum of the oscillation amplitudes in the high temperature region and the low temperature region is too large, an excessive temperature gradient will be generated, resulting in the crystal growth being too fast, and the quality of the obtained AgCrSe ₂ crystals will also decrease. The temperature oscillation amplitudes of the above ranges are more conducive to meet the needs of increasing the deposition rate of the crystal steps and increasing the thickness of the crystal.

According to yet another specific embodiment of the present invention, the oscillation heating temperature curve may include a plurality of oscillation periods, and in at least two consecutive oscillation periods, the duration of the low temperature plateau and the duration of the high temperature plateau in the next oscillation period may both be within the same period as the previous oscillation period. 10 to 50%, for example, it can be extended by 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc.; The high/low temperature plateau of the next cycle is gradually increased on the basis of the previous cycle. The inventor found that in the process of temperature oscillation, the temperature from high to low is to increase the crystal step deposition, the heat preservation is for the step deposition and stability, and the temperature from low to high is for the crystal to grow on the deposited steps, and to achieve size increase, with the increase in size. As the crystal size becomes larger, the number of steps that can be accommodated increases, and the required step deposition time and stabilization time increase accordingly. When the oscillation period is extended to the above range, the thickness of the crystal can be significantly increased within the same crystal growth time.

According to a specific embodiment of the present invention, the growth of the AgCrSe ₂ single crystal in the present invention adopts a horizontal gas phase transport method, and adopts a horizontal double-temperature zone tube furnace. The implementation method may include: according to the chemical formula AgCrSe ₂ ) pure elemental particles or powder, according to the chemical ratio for ingredients; put the raw materials into a clean high-energy ball mill tank, fill with high-purity argon, and ball mill for 2-5 hours; put the ground fine powder in a quartz tube, pump Vacuum to 10 ^-4 Pa to seal the tube; put the filled quartz tube into the muffle furnace, and anneal at 450-800 ℃ for 10-20 hours; put the synthesized AgCrSe ₂ polycrystalline powder and the transmission medium CrCl ₃ or I ₂ is mixed in a certain proportion and repackaged into a quartz crucible and vacuum-sealed, and put into a horizontal double-temperature zone tube furnace, one end of the raw material is placed in a high-temperature zone, an oscillation temperature curve is set, and the temperature is kept for 5-15 days for crystal growth.

To sum up, the method for preparing large-size AgCrSe ₂ crystals with anisotropy in the above-mentioned embodiments of the present invention can make full use of the AgCrSe ₂ crystal growth process by improving the crystal growth conditions and adopting the gas phase transport method with an oscillating heating temperature curve. The energy required for the formation and diffusion of the intermediate steps is different, and various process parameters in the growth process such as the oscillating temperature curve, the gradient of the high and low temperature regions, and the proportion of the transport medium are controlled, and a large number of macroscopic crystal growth steps are formed cyclically to promote strong anisotropy. The continuous growth of AgCrSe ₂ crystals with anisotropic structure can not only improve the size, thickness and quality of AgCrSe ₂ crystals and obtain large-sized crystals with anisotropy, but also help to obtain high thermoelectric transport properties in special directions. In particular, AgCrSe ₂ crystal materials with a size up to 7 mm and a thickness up to 0.43 mm can be fabricated by this method.

Embodiments of the present invention are described in detail below. The embodiments described below are exemplary, only for explaining the present invention, and should not be construed as limiting the present invention. If no specific technique or condition is indicated in the examples, the technique or condition described in the literature in the field or the product specification is used. The reagents or instruments used without the manufacturer's indication are conventional products that can be obtained from the market.

Comparative Example 1

The synthesized AgCrSe ₂ polycrystalline powder 1g and 15mg of the transport medium CrCl ₃ were mixed and evacuated to 10 ^-4 Pa to seal the tube (as shown in Figure 2), put into a double-temperature zone tube furnace, and grown by conventional gas phase transport. The temperature of the high temperature section is set to 1143K, the low temperature section is set to 1083K, the temperature is raised to the target temperature after 5 hours, and the temperature is kept for 240 hours. Finally, the temperature is lowered to 373K after 17 hours, and the power is turned off. The heating procedure is shown in FIG. 3 , and the resulting wafer is 12 μm thick, as shown in FIG. 4 .

Example 1

The synthesized AgCrSe ₂ polycrystalline powder 1 g and 8 mg of the transport medium CrCl ₃ were mixed and evacuated to 10 ^-4 Pa to seal the tube, put into a dual-temperature zone tube furnace, and crystallized according to the improved gas-phase transport method. The temperature of the high temperature section is set to 1123K, and the low temperature section is set to 1103K. After 5 hours, the temperature is raised to the target temperature. Then, the low temperature zone is kept at a constant temperature, and the high temperature zone is subjected to temperature oscillation to adjust the saturated vapor pressure. First hold at 1123K for 7h, then heat up to 1143K for 1h and hold for 20h, then cool down to 1123K for 7 hours after 1h, cycle and shake for 8 times, and finally cool down to 373K after 17 hours and turn off the power to cool to room temperature with the furnace, the crystal grows Finish. The heating procedure is shown in FIG. 5 , and the resulting wafer is 170 μm thick, as shown in FIG. 6 .

Example 2

1g of synthesized AgCrSe ₂ polycrystalline powder and 8mg of transmission medium CrCl ₃ (7mg)+I ₂ (1mg) were mixed and evacuated to 10 ^{- 4} Pa to seal the tube, and put into a double-temperature zone tube furnace. The vapor phase transport method for crystal growth. The temperature of the high temperature section is set to 1138K, and the low temperature section is set to 1123K. After 5 hours, the temperature is raised to the target temperature, and then the low temperature area is kept constant, and the high temperature area is subjected to temperature oscillation. First hold at 1138K for 7h, then heat up to 1173K for 0.5h and hold for 10h, then cool down to 1138K for 1 hour after 0.5h, then heat up to 1173K for 0.5h and hold for 11 hours. Increase the time by 10% and cycle 10 times. Finally, the temperature was lowered to 373K after 17 hours, the power was turned off, and the furnace was cooled to room temperature, and the crystal growth was completed. The heat preservation and heating procedure is shown in FIG. 7 , and the obtained wafer has a thickness of 430 μm, as shown in FIG. 8 .

Results and conclusions: The characteristic peaks of XRD of the wafers prepared in Examples 1 and 2 are completely consistent with the characteristic peaks of the AgCrSe ₂ single crystal sample in Figure 9, indicating that the AgCrSe ₂ single crystal sample was successfully prepared in Examples 1 and 2. It can be seen from the comparison of Example 1 and Comparative Example 1 that, under the premise that the total crystal growth time is equivalent, the thickness of the final crystal obtained can be significantly increased by using the oscillating heating process; Under the same premise, increasing the number of oscillation cycles and gradually prolonging the holding time of the high and low temperature platforms in the oscillation cycle can further significantly increase the thickness of the final crystals.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Claims (12)

1. Preparation of large-size AgCrSe with anisotropy₂A method of crystallizing, comprising:

(1) mixing AgCrSe₂Mixing the polycrystalline powder with a transmission medium, and putting the mixture into a sealable container for vacuumizing and sealing;

(2) heating the sealed container in a horizontal double-temperature-zone heating environment, wherein one side of the container, which is used for containing the mixture, is positioned in a high-temperature zone, a vibration heating temperature curve is adopted in the heating process, the heating time is 5-15 days,

wherein:

in the step (1), the transmission medium is CrCl₃Said transmission medium and said AgCrSe₂The mass-volume ratio of the polycrystalline powder is 0.1-1 mg/cm³(ii) a Or the transmission medium is CrCl₃And I₂Mixture of (1), CrCl₃And I₂Is not less than 1, the transmission medium and the AgCrSe₂The mass-volume ratio of the polycrystalline powder is 0.15-1.2 mg/cm³；

In the step (2), the dual-temperature region comprises a high-temperature region and a low-temperature region, and at least one of the high-temperature region and the low-temperature region adopts a vibration heating temperature curve; the temperature range of the low-temperature region is 750-870 ℃, the temperature of the high-temperature region is 25-70 ℃ higher than that of the low-temperature region, and the temperature gradient between the high-temperature region and the low-temperature region is 1-10 ℃/cm; when only the high-temperature zone or only the low-temperature zone adopts a vibration heating temperature curve, the temperature vibration amplitude of the vibration heating temperature curve is 10-40 ℃, and each vibration period is independently 1-40 hours; when the high-temperature area and the low-temperature area adopt oscillation heating temperature curves at the same time, the temperature oscillation amplitudes of the oscillation heating temperature curves of the high-temperature area and the low-temperature area are respectively and independently 5-20 ℃, and each oscillation period is respectively and independently 1-40 h;

in the step (2), the oscillation heating temperature curve includes at least one oscillation period, and each oscillation period independently includes a low-temperature platform, a temperature raising section, a high-temperature platform, and a temperature lowering section: when the oscillation heating temperature curve comprises a plurality of oscillation periods, in at least two continuous oscillation periods, the total duration of the next oscillation period is prolonged by 10-50% on the basis of the total duration of the previous oscillation period.

2. The method according to claim 1, wherein the step (2) is carried out in a horizontal dual-temperature zone tube furnace, the sealable container is a quartz crucible, and the diameter of the quartz crucible is 10-30 mm.

3. The method of claim 1 or 2, wherein the AgCrSe is₂The polycrystalline powder is prepared by the following steps:

(i) according to AgCrSe₂Mixing the single particles of Ag, Cr and Se according to the stoichiometric ratio;

(ii) placing the mixture in a ball milling tank and carrying out ball milling treatment under inert atmosphere;

(iii) placing the ground fine powder in a sealable container, and vacuumizing and sealing;

(iv) and (4) placing the sealed container in a high-temperature environment for annealing treatment.

4. The method of claim 3, wherein in step (i), the elemental particles have a purity of not less than 4N.

5. The method according to claim 3, wherein in the step (ii), the ball milling treatment time is 1-10 h.

6. A process according to claim 3, wherein in step (iii), a vacuum is applied directly to 10%^-4Pa and sealing; or, vacuumizing and filling inert gas, repeating for 3 times, and vacuumizing to 10^-1Pa and sealing.

7. The method according to claim 3, wherein in the step (iv), the temperature of the annealing treatment is 450-800 ℃ and the time is 5-50 h.

8. The method of claim 1 or 2, wherein the AgCrSe is₂The polycrystalline powder is prepared by the following steps:

(I) according to AgCrSe₂Mixing the single particles of Ag, Cr and Se according to the stoichiometric ratio;

(II) cold-pressing the mixture into blocks, and placing the block raw materials into a sealable container for vacuumizing and sealing;

and (III) placing the sealed container in a high-temperature environment for annealing treatment.

9. The method of claim 8, wherein in step (I), the elemental particles have a purity of not less than 4N.

10. The method of claim 8, wherein in step (II), the vacuum is directly applied to 10%^-4Pa and sealing; or, vacuumizing and filling inert gas, repeating for 3 times, and vacuumizing to 10^-1Pa and sealing.

11. The method according to claim 8, wherein in the step (III), the annealing treatment is carried out at a temperature of 600 to 900 ℃ for 5 to 50 hours.

12. The method according to claim 1, wherein when the oscillating heating temperature profile comprises a plurality of oscillating periods, at least one of the duration of the low temperature plateau, the duration of the temperature raising period, the duration of the high temperature plateau and the duration of the temperature lowering period of the next oscillating period in at least two consecutive oscillating periods is extended by 10-50% based on the duration of the corresponding period of the previous oscillating period.

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