CN113564714A - Anisotropic large-size crystal and AgCrSe2Preparation method of (1) - Google Patents
Anisotropic large-size crystal and AgCrSe2Preparation method of (1) Download PDFInfo
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Abstract
The invention discloses an anisotropic large-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 high thermoelectric transport performance in special direction, for example, the size can reach 7 mm, and the thickness is highAgCrSe up to 0.43 mm2A crystalline material.
Description
Technical Field
The invention belongs to the field of materials, and particularly relates to an anisotropic large-size crystal and AgCrSe2The preparation method of (1).
Background
The thermoelectric material is an environment-friendly green energy conversion material which can realize direct interconversion of heat energy and electric energy, can directly convert heat energy which is difficult to collect by other methods, such as industrial waste heat and automobile exhaust waste heat, into electric energy, and has very important significance for breaking through the limitation of the utilization rate of the traditional fossil energy.
The performance of thermoelectric materials is generally characterized by a dimensionless thermoelectric figure of merit, zT ═ S2σ T/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 coefficient, high electrical conductivity and low thermal conductivity. AgCrSe2Is a super-ionic conductor material with typical intercalation structure characteristics and at the phase transition temperature TcIn the following, Ag ions are orderly arranged in the center of a tetrahedron formed by four Se atoms; and at TcIn the above, Ag ions are randomly arranged at the center position of an equivalent Se atom tetrahedron to generate a liquid-like behavior, so that AgCrSe is obtained2Has the characteristics of 'electronic crystal' and 'phonon glass', and can obtain extremely low lattice thermal conductivity (0.4-0.5 W.K)-1·m-1). However, the origin of the extremely low lattice thermal conductivity is controversial, and partial research supports that the propagation of the acoustic support of the transverse wave is caused by disorder and the propagation of the acoustic support of the transverse wave is inhibited by ion diffusion, so that the analysis and explanation based on neutron scattering and an ultrafast transmission electron microscope are required to solve the controversial. Recent studies on layered single crystal materials have shown that the thermoelectric properties of layered materials in particular directions are significantly improved due to bonding anisotropy, e.g. SnSe, Bi2And Te. The existing research shows that the AgCrS with isomorphism2The electric transport performance in the in-plane direction is found to be more than hundred times higher than that out-of-plane in the single crystal material; and, in AgCrSe2Higher electrical conductivity was found in the polycrystalline sample in the in-plane direction, while thermal conductance and seebeck coefficient were substantially consistent with the out-of-plane direction. Therefore, there is a need for AgCrSe having a layered crystal structure2Large-size single crystals are grown so as to study the problem of low thermal conductivity on the one hand and obtain high thermoelectric performance in the material plane on the other hand. Thus, how to grow AgCrSe with strong anisotropy2The large-size crystal has very important significance.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, it is an object of the invention to provide anisotropic large-size crystals and AgCrSe2The preparation method of (1). The preparation method adopts the oscillation heating temperature curve heating in the crystal growth process, not only can obtain large-size crystals with anisotropy, but also is beneficial to obtaining high thermoelectric transport performance in a special direction aiming at thermoelectric materials.
The present application is mainly proposed based on the following findings of the inventors:
the inventors have discovered that studying the manner in which fast ions move and their effects on the energy bands and phonons can explain the source of thermal and electrical anisotropy from the atomic to even electronic level and promote the development of fast ionic materials to even condensed state physics. On the basis of different energies required by step formation and diffusion in the crystal growth process, a large number of macroscopic crystal growth steps can be formed circularly by controlling various process parameters in the growth process such as an oscillation temperature curve, high and low temperature region gradients, transport medium proportion and the like, and the continuous growth of large-size crystals with strong anisotropic structures is promoted.
To this end, according to one aspect of the invention, a method of preparing anisotropic large-size crystals is proposed. According to the embodiment of the invention, the method adopts an oscillating heating temperature curve for heating in the crystal growth process. In the prior art, the size, thickness and quality of the crystal material can be improved by adopting the method, the anisotropic large-size crystal can be obtained, and the thermoelectric material is favorable for obtaining the thermoelectric transport performance in a special direction.
In addition, the method for preparing anisotropic large-sized crystals according to the above embodiment of the present invention may further have the following additional technical features:
in some embodiments of the present invention, a horizontal dual-temperature-zone vapor transport growth method is adopted in the crystal growth process, the dual-temperature-zone includes a low-temperature zone and a high-temperature zone, and at least one of the high-temperature zone and the low-temperature zone adopts an oscillation heating temperature curve.
According to the bookIn still another aspect of the present invention, the present invention provides a method for preparing large-sized AgCrSe having anisotropy2A method for producing the crystal. According to an embodiment of the invention, the method comprises:
(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.
The inventor finds that AgCrSe2The crystal material is a super-ion conductor material with typical intercalation structure characteristics, the step deposition speed is lower than the drift speed in the crystal growth process, the deposition speed of the step, namely the atomic deposition speed, can be increased by adopting temperature oscillation, and the crystal thickness can be increased only when the deposition speed is increased; moreover, if the heating time is too short, it is not possible to ensure sufficient crystal growth, and it is difficult to obtain AgCrSe of a desired large size2And (4) crystals. Preparation of Large-sized AgCrSe with anisotropy Using the above-described embodiments of the invention2The method of crystallization can utilize AgCrSe2The energy needed by the step formation and diffusion in the crystal growth process is different, and various process parameters in the growth process such as oscillation temperature curve, high and low temperature region gradient, transport medium proportion and the like are controlled, so that a large number of macroscopic crystal growth steps are formed in a circulating manner, and the AgCrSe with a strong anisotropic structure is promoted2The crystal grows continuously, thereby not only improving AgCrSe2The 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, specifically, the AgCrSe with the size up to 7 mm and the thickness up to 0.43 mm can be prepared by adopting the method2A crystalline material.
In addition, the preparation of large-sized AgCrSe having anisotropy according to the above-described embodiments of the present invention2The method of crystallization may also have the following additional technical features:
in some embodiments of the invention, in 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。
In some embodiments of the invention, in step (1), the transport 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 some embodiments of the present invention, in step (2), the dual-temperature region includes a high-temperature region and a low-temperature region, and at least one of the high-temperature region and the low-temperature region adopts an oscillating heating temperature curve.
In some embodiments of the present invention, the 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 invention, the temperature of the low temperature region ranges from 750 ℃ to 870 ℃, and the temperature of the high temperature region is 25 ℃ to 70 ℃ higher than that of the low temperature region.
In some embodiments of the present invention, the oscillating heating temperature profile includes at least one oscillation period, and each oscillation period independently includes a low temperature stage, a temperature rising stage, a high temperature stage, and a temperature lowering stage.
In some embodiments of the present invention, only the high temperature region or only the low temperature region adopts an oscillation heating temperature curve, the temperature oscillation amplitude of the oscillation heating temperature curve is 10 to 40 ℃, and each oscillation period is independently 1 to 40 hours.
In some embodiments of the present invention, the high temperature region and the low temperature region adopt oscillation heating temperature curves at the same time, the temperature oscillation amplitude of the oscillation heating temperature curves of the high temperature region and the low temperature region is 5 to 20 ℃ respectively and independently, and each oscillation period is 1 to 40 hours respectively and independently.
In some embodiments of the present invention, the oscillating heating temperature profile includes a plurality of oscillating periods, and in at least two consecutive oscillating periods, a total duration of a next oscillating period is extended by 10 to 50% of a total duration of a previous oscillating period.
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, at least one of a low temperature stage duration, a temperature raising period duration, a high temperature stage duration, and a temperature lowering period duration of a next oscillating period is extended by 10 to 50% based on a duration of a corresponding stage of a previous oscillating period.
In some embodiments of the invention, the temperature gradient between the high temperature zone and the low temperature zone is 1-10 ℃/cm.
In some embodiments of the invention, 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.
In some embodiments of the invention, in step (i), the purity of the elemental particles is not less than 4N.
In some embodiments of the present invention, in the step (ii), the time of the ball milling treatment is 1 to 10 hours.
In some embodiments of the invention, step (iii) is directly evacuated to 10 deg.f-4Pa and sealing; or, vacuumizing and filling inert gas, repeating for 3 times, and vacuumizing to 10-1Pa and sealing.
In some embodiments of the present invention, in the step (iv), the temperature of the annealing treatment is 450 to 800 ℃ and the time is 5 to 50 hours.
In some embodiments of the invention, 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.
In some embodiments of the invention, in step (I), the elemental particles have a purity of not less than 4N.
In some embodiments of the invention, step (II) is directly evacuated to 10 deg.F-4Pa and sealing; or, vacuumizing and filling inert gas, repeating for 3 times, and vacuumizing to 10-1Pa and sealing.
In some embodiments of the present invention, in the step (III), the annealing temperature is 600 to 900 ℃ and the annealing time is 5 to 50 hours.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a flow chart of a method of preparing large size AgCrSe2 crystals with anisotropy according to one embodiment of the invention;
fig. 2 is a schematic view of the growth of a horizontal dual-temperature-zone vapor transport crystal according to an embodiment of the present invention, wherein a right circle is a high-temperature-zone heating body, a left circle is a low-temperature-zone heating body, and a dotted line is a transport medium transport manner.
FIG. 3 is a graph showing a heating temperature profile for crystal growth of comparative example 1 according to the present invention;
FIG. 4 shows AgCrSe grown by conventional vapor transport method according to comparative example 1 of the present invention2A wafer map;
FIG. 5 is a graph showing a heating temperature profile for crystal growth according to example 1 of the present invention;
FIG. 6 is AgCrSe grown according to example 1 of the present invention2A wafer map;
FIG. 7 is a graph of heating temperature for crystal growth according to example 2 of the present invention;
FIG. 8 is AgCrSe grown according to example 2 of the present invention2A wafer map;
FIG. 9 is a block diagram of an embodiment of the present inventionPreparation of examples AgCrSe2XRD (X-ray diffraction) patterns of ball-milled and annealed samples during polycrystalline sample preparation and AgCrSe obtained by oscillating and heating the annealed samples to realize crystal growth2The XRD pattern of the wafer was compared to a standard card.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
It should be noted that the innovation point of the invention is based on the improvement of the heating mode of the growth of the gas-phase transport crystal, and the obtained oscillation temperature field has the following characteristics: and periodically regulating saturated vapor pressure in the growth process to obtain continuous growth conditions of the crystal. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, any crystal growth method similar or equivalent to the described contents can be applied to the method of the present application. The preferred embodiments and materials described herein are intended to be exemplary only.
According to one aspect of the present invention, a method of preparing anisotropic large-sized crystals is presented. According to the embodiment of the invention, the method adopts an oscillating heating temperature curve for heating in the crystal growth process. Preferably, a horizontal double-temperature-zone vapor transport growth method can be adopted in the crystal growth process, for example, a horizontal double-temperature-zone tube furnace can be used for horizontal double-temperature-zone heating; the dual-temperature zone includes a low-temperature zone and a high-temperature zone, wherein at least one of the high-temperature zone and the low-temperature zone may adopt an oscillation heating temperature curve, for example, a single-temperature zone oscillation heating may be adopted, only the high-temperature zone or only the single-temperature zone may adopt an oscillation heating temperature curve, or a dual-temperature zone oscillation heating may be adopted, that is, the high-temperature zone and the low-temperature zone may adopt an oscillation heating temperature curve at the same time. The inventor finds that the energy required by the step formation and diffusion in the crystal growth process is different, and on the basis, a large number of macroscopic crystal growth steps can be formed in a circulating mode by controlling various process parameters in the growth process such as an oscillation temperature curve, high and low temperature region gradients, transport medium proportion and the like, so that the continuous growth of large-size crystals with strong anisotropic structures is promoted. Therefore, compared with the prior art, the method for preparing the anisotropic large-size crystal can not only improve the size, thickness and quality of the crystal material and obtain the anisotropic large-size crystal, but also is beneficial to obtaining the thermoelectric transport performance in a special direction aiming at the thermoelectric material.
According to still another aspect of the present invention, there is provided a method for preparing large-sized AgCrSe having anisotropy2A method for producing the crystal. According to an embodiment of the invention, as shown in fig. 1, the method comprises:
s100: mixing AgCrSe2The polycrystalline powder and the transmission medium are mixed, and the mixture is placed in a sealable container to be vacuumized and sealed. The finally prepared AgCrSe can be further improved by vacuumizing the mixture2Purity and thermoelectric properties of the crystal.
According to a specific embodiment of the present invention, the transmission medium may be CrCl3，CrCl3With AgCrSe2The mass-volume ratio of the polycrystalline powder can be 0.1-1 mg/cm3For example, it may be 0.1mg/cm3、0.2mg/cm3、0.3mg/cm3、0.4mg/cm3、0.5mg/cm3、0.6mg/cm3、0.7mg/cm3、0.8mg/cm3Or 0.9mg/cm3The inventor finds that if the using amount of the transmission medium is too small, the crystal nucleus cannot be rapidly grown, and if the using amount of the transmission medium is too large, the crystal nucleus and the crystal growth are too fast, so that the crystal size is small as a whole, the number is large, and the quality of the crystal is difficult to control. In the invention, CrCl is controlled3The addition amount is in the range, which is more favorable for obtaining AgCrSe with larger size and higher purity2Crystals of AgCrSe2The crystal has high thermoelectric transport performance in a specific direction.
According to still another embodiment of the inventionFor example, the transport medium may be CrCl3And I2Mixture of (1), CrCl3And I2Is not less than 1, for example the mass ratio may be 1.5, 1.2 or 1, etc., CrCl3And I2With AgCrSe2The mass-volume ratio of the polycrystalline powder is 0.15-1.2 mg/cm3For example, it may be 0.15mg/cm3、0.2mg/cm3、0.3mg/cm3、0.4mg/cm3、0.5mg/cm3、0.6mg/cm3、0.7mg/cm3、0.8mg/cm3、0.9mg/cm3、1mg/cm3、1.1mg/cm3Or 1.2mg/cm3And the like. The inventors have found that CrCl can be utilized3Promoting crystal growth while utilizing I2Promote step deposition if CrCl3And I2The total dosage of the crystal nucleus is too little, the growth of the crystal nucleus can not be rapidly realized, and if the total dosage of the crystal nucleus and the crystal nucleus is too much, the crystal nucleus and the growth are too fast, so that the whole crystal size is small, the quantity is too much, and the situation that the crystal quality is difficult to control can also occur. In the invention, CrCl is controlled3And I2The proportion and the addition range are more favorable for obtaining AgCrSe with larger size, larger thickness and higher purity2Crystals of AgCrSe2The crystal has high thermoelectric transport performance in a specific direction.
According to an embodiment of the invention, AgCrSe is used in the invention2The source of the polycrystalline powder is not particularly limited and may be selected by those skilled in the art according to practical needs, for example, AgCrSe2The polycrystalline powder can be a commercial product, and can also be synthesized by Ag, Cr and Se according to a stoichiometric ratio.
According to one embodiment of the invention, AgCrSe2The polycrystalline powder can be prepared by the following steps: (i) according to AgCrSe2The elementary particles Ag, Cr and Se are mixed according to the stoichiometric ratio, wherein the purity of each elementary particle can be not less than 4N, and can be 99.999% or 99.9999%, and the like; (ii) placing the mixture in a ball milling tank and performing ball milling treatment in an inert atmosphere, for example, the mixture can be placed in a clean high-energy ball milling tank, filled with high-purity argon gas, and the ballsGrinding for 1-10 hours, specifically 3 hours, 5 hours, 7 hours or 9 hours; (iii) placing the ground fine powder in a sealable container, and evacuating and sealing, for example, the ground fine powder can be directly charged into a quartz tube and evacuated to 10 deg.C-4Sealing the pipe by Pa; or vacuumizing first and then filling inert gas, repeating for 3 times, and vacuumizing to 10-1Pa and sealing the tube, thereby further improving the purity of the prepared product; (iv) the sealed container is placed in a high-temperature environment for annealing treatment, for example, the quartz tube filled with the material can be placed in a muffle furnace for annealing at the temperature of 450 ℃ and 800 ℃ for 5-50 hours, specifically, the annealing temperature can be 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃ or 800 ℃, and the like, and the annealing time can be 10h, 15h, 20h, 25h, 30h, 35h, 40h or 45h, and the like2Quality of polycrystalline samples. Wherein, FIG. 9 shows AgCrSe obtained by ball-milling a sample, annealing the sample, and performing oscillation heating on the annealed sample to realize crystal growth2The XRD pattern of the wafer is compared with that of a standard card, and the AgCrSe obtained by annealing can be seen from figure 92Polycrystalline sample and AgCrSe2The images of the fitting peaks (standard crystal structures) are completely consistent, which shows that AgCrSe is successfully synthesized after annealing treatment2Polycrystalline samples.
According to yet another embodiment of the invention, AgCrSe2The polycrystalline powder can be prepared by the following steps: (I) according to AgCrSe2The elementary particles Ag, Cr and Se are mixed according to the stoichiometric ratio, wherein the purity of each elementary particle can be not less than 4N, and can be 99.999% or 99.9999%, and the like; (II) Cold pressing the mixture into blocks and placing the block material in a sealable container, evacuating and sealing, for example, the block material may be placed in a quartz tube and evacuated to 10 deg.C-4Sealing the pipe by Pa; or vacuumizing first and then filling inert gas, repeating for 3 times, and vacuumizing to 10-1Pa and sealing the tube, thereby further improving the purity of the prepared product; (III) annealing the sealed container in a high temperature environment, e.g. byThe quartz tube filled with the materials can be put into a muffle furnace and annealed at the temperature of 600 plus materials and 900 ℃ for 5-50 hours, specifically, the annealing temperature can be 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃ or 900 ℃ and the like, and the time can be 10h, 15h, 20h, 25h, 30h, 35h, 40h or 45h and the like, thereby not only considering the annealing efficiency, but also ensuring the finally obtained AgCrSe2Quality of polycrystalline samples.
S200: and (3) heating the sealed container in a horizontal double-temperature-zone heating environment, so that one side of the container, which contains the mixture, is located in a high-temperature zone (as shown in figure 2), wherein a vibration heating temperature curve is adopted in the heating process, and the heating time is 5-15 days. The inventor finds that AgCrSe2The crystal material is a super-ion conductor material with typical intercalation structure characteristics, the step deposition speed is lower than the drift speed in the crystal growth process, the deposition speed of the step, namely the atomic deposition speed, can be increased by adopting temperature oscillation, and the crystal thickness can be increased only when the deposition speed is increased; moreover, if the heating time is too short, it is not possible to ensure sufficient crystal growth, and it is difficult to obtain AgCrSe of a desired large size2The crystal is more beneficial to obtaining the large-size AgCrSe by adopting the vibration heating mode and the heating time2And (4) crystals.
According to an embodiment of the present invention, the crystal growth process may 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, the lengths of the high-temperature zone and the low-temperature zone of the horizontal dual-temperature zone tube furnace may be respectively 30cm, as understood with reference to the directions 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 may be 1-10 ℃/cm, for example, 1-5 ℃/cm, 2 ℃/cm, 4 ℃/cm, 6 ℃/cm, or 8 ℃/cm, etc., the sealable container may be a quartz crucible, and the diameter of the quartz crucible may be 10-30 mm. The inventors found that if the temperature gradient between the high temperature region and the low temperature region is too small, crystal growth is too slow; if the temperature gradient between the high-temperature area and the low-temperature area is too large, crystallization is too fast, on one hand, nucleation is too much and growth is difficult, on the other hand, one-dimensional whisker crystals appear, and high-quality crystals can be obtained only in a reasonable gradient range; in the invention, the temperature gradient is controlled between the two components, andis beneficial to obtaining AgCrSe with larger size, larger thickness and higher purity2Crystals of AgCrSe2The crystal has high thermoelectric transport performance in a specific direction.
According to another embodiment of the present invention, at least one of the high temperature region and the low temperature region may adopt an oscillation heating temperature curve, and the inventors found that the purpose of increasing the deposition rate of the step and increasing the crystal thickness can be achieved by adopting either single-temperature region oscillation heating or dual-temperature region oscillation heating, and that the oscillation effects of the single-temperature region and the dual-temperature region are close to each other under the condition that the sum of the oscillation temperature amplitudes is close to each other, and 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 the raw materials are all utilized.
According to another embodiment of the present invention, the temperature of the low temperature region may be 750 to 870 ℃, for example 770 ℃, 790 ℃, 810 ℃, 830 ℃, 850 ℃ or 870 ℃, and the temperature of the high temperature region may be 25 to 70 ℃ higher than that of the low temperature region, for example, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃ or 70 ℃, and the inventors found that if the temperature of the low temperature region or the high temperature region is too low, not only the reaction is slow, the crystal growth cycle is long, but also it is difficult to make the AgCrSe have a long crystal growth cycle2Fully reacting the polycrystalline powder sample; if the temperature is too high, the crystal growth is too fast, and the difficulty of controlling the product quality is increased. According to the invention, the temperature ranges of the low-temperature region and the high-temperature region are respectively controlled, so that AgCrSe with expected size and high purity can be obtained more conveniently2Crystals of AgCrSe2The crystal has high thermoelectric transport performance in a specific direction.
According to another embodiment of the present invention, the oscillating heating temperature profile may include at least one oscillating period, each oscillating period independently includes a low temperature stage, a temperature raising stage, a high temperature stage and a temperature lowering stage, for example, referring to fig. 5 or fig. 7, the temperature may be raised to a first temperature in advance, after the temperature is maintained at the first temperature for a period of time, the temperature is raised to a second temperature within the oscillating temperature range, then the temperature is maintained at the second temperature for a period of time, and then the temperature is lowered to the first temperature,the incubation at the first temperature may then continue into the next oscillation cycle. Wherein, in the temperature shock process, the growth on the step of deposit is realized in order to realize the crystal from low temperature platform to high temperature platform, realizes the size increase, and the purpose of heat preservation is for step deposit and stable, and the deposit is in order to increase the crystal step from high temperature platform to low temperature platform. Preferably, the oscillation heating temperature curve may include a plurality of oscillation cycles, for example, the number of oscillation cycles may be 1 to 100, such as 5, 10, 20, 50, 80, or 100, and the inventors found that increasing the number of oscillation cycles may allow the crystal growth to be more sufficient until the raw material is fully utilized, which may be more beneficial to improving the finally prepared AgCrSe2The size of the crystals.
According to another embodiment of the present invention, a single-temperature zone oscillation heating mode may be adopted in the crystal growth process, that is, an oscillation heating temperature curve is adopted only in the high-temperature zone or only in the low-temperature zone, the temperature oscillation amplitude of the adopted oscillation heating temperature curve may be 10 to 40 ℃, for example, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃ or 40 ℃, each oscillation period may be 1 to 40 hours, for example, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours or 40 hours, respectively, and the inventor finds that, when single-temperature zone oscillation heating is adopted, if the oscillation amplitude is too small, the effect of accelerating step deposition is not performed, and if the oscillation amplitude is too large, an excessive temperature gradient is generated, which results in too fast crystal growth, the obtained AgCrSe2The quality of the crystal is also reduced, and the control of the temperature oscillation amplitude range is more favorable for meeting the requirements of increasing the step deposition speed of the crystal and improving the thickness and the quality of the crystal. It should be noted that the temperature oscillation amplitude in the present invention refers to the temperature difference between the high temperature platform and the low temperature platform in the oscillation heating temperature curve.
According to another embodiment of the present invention, the crystal growth process may adopt a dual-temperature zone oscillation heating manner, that is, the high-temperature zone and the low-temperature zone may adopt oscillation heating temperature curves at the same time, and the temperature oscillation amplitude of the oscillation heating temperature curves of the high-temperature zone and the low-temperature zone may be 5 to 20 ℃, for example, 5 ℃, 8 ℃, 11 ℃, 14 DEG C17 ℃ or 20 ℃ and the like, wherein each oscillation period can be 1-40 h independently, for example, 5h, 10h, 15h, 20h, 25h, 30h, 35h or 40h and the like, and the inventor finds that when the double-temperature-zone oscillation heating is adopted, if the sum of the oscillation amplitudes of the high-temperature zone and the low-temperature zone is too small, the effect of accelerating step deposition cannot be achieved, and if the sum of the oscillation amplitudes of the high-temperature zone and the low-temperature zone is too large, an overlarge temperature gradient is generated, so that the crystal growth is too fast, the obtained AgCrSe is obtained2The quality of the crystal is also reduced, and the control of the temperature oscillation amplitudes of the high-temperature area and the low-temperature area to be in the ranges is more favorable for meeting the requirements of increasing the step deposition speed of the crystal and improving the thickness of the crystal.
According to another embodiment of the present invention, the oscillating heating temperature curve may include a plurality of oscillating periods, and in at least two consecutive oscillating periods, the low temperature platform duration and the high temperature platform duration of the next oscillating period may be extended by 10% to 50% on the basis of the previous oscillating period, for example, by 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%; preferably, the high/low temperature stage of the latter cycle may be gradually increased on the basis of the former cycle during the plurality of oscillation cycles. The inventor finds that in the temperature oscillation process, the temperature is increased from high to low to increase the step deposition of the crystal, the heat preservation is performed for the step deposition and stabilization, the temperature is increased from low to high to grow the crystal on the deposited step, the size is increased, the number of steps capable of being accommodated is increased along with the increase of the size of the crystal, the required step deposition time and the required step stabilization time are correspondingly increased, the increase of the thickness of the crystal is more facilitated by prolonging the duration of the oscillation period, particularly the duration of the heat preservation period, and particularly when the duration of the oscillation period is within the range, the thickness of the crystal can be remarkably increased within the same crystal growth time.
According to one embodiment of the invention, AgCrSe is used in the invention2The single crystal growth is carried out by adopting a horizontal gas phase transportation method and a horizontal double-temperature-zone tube furnace, and the implementation method can comprise the following steps: according to the chemical formula AgCrSe2The method adopts simple substance particles or powder with the purity of 5N (99.999 percent) to prepare the materials according to the chemical proportion(ii) a Putting the raw materials into a high-energy ball milling tank which is cleaned, filling high-purity argon, and carrying out ball milling for 2-5 hours; loading the ground fine powder into a quartz tube, and vacuumizing to 10%-4Sealing the pipe by Pa; putting the quartz tube filled with the materials into a muffle furnace, and annealing for 10-20 hours at the temperature of 450-; the synthesized AgCrSe2Polycrystalline powder and transmission medium CrCl3Or I2Mixing the raw materials according to a certain proportion, sealing the mixture in a quartz crucible, vacuumizing and sealing the quartz crucible, putting the quartz crucible into a horizontal double-temperature-zone tube furnace, placing one end of the raw materials in a high-temperature zone, setting an oscillation temperature curve, and preserving heat for 5-15 days to grow crystals.
In conclusion, the preparation of large-size AgCrSe with anisotropy according to the above embodiment of the invention2The method of the crystal can fully utilize AgCrSe by improving the growth condition of the crystal and adopting a gas phase transportation method with an oscillation heating temperature curve2The energy needed by the step formation and diffusion in the crystal growth process is different, and various process parameters in the growth process such as oscillation temperature curve, high and low temperature region gradient, transport medium proportion and the like are controlled, so that a large number of macroscopic crystal growth steps are formed in a circulating manner, and the AgCrSe with a strong anisotropic structure is promoted2The crystal grows continuously, thereby not only improving AgCrSe2The 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, specifically, the AgCrSe with the size up to 7 mm and the thickness up to 0.43 mm can be prepared by adopting the method2A crystalline material.
The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
Comparative example 1
The synthesized AgCrSe2Polycrystalline powder 1g and 15mg of transmission medium CrCl3Mixing and vacuumizing to 10-4Pa sealing the tube (as shown in the figure)2) putting the material into a double-temperature-zone tube furnace, setting the temperature of a high-temperature section to be 1143K and the temperature of a low-temperature section to be 1083K according to a conventional vapor transport growth mode, heating the material to a target temperature after 5 hours, preserving the heat for 240 hours, finally cooling the material to 373K after 17 hours, turning off a power supply, cooling the material to room temperature along with the furnace, and finishing crystal growth. 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 AgCrSe2Polycrystalline powder 1g and transmission medium CrCl 8mg3Mixing and vacuumizing to 10-4And Pa, sealing the tube, putting the tube into a double-temperature-zone tube furnace, and growing crystals according to an improved gas phase transport method. The temperature of the high-temperature section is set to 1123K, the temperature of the low-temperature section is set to 1103K, the temperature is raised to the target temperature after 5 hours, then the low-temperature section keeps constant temperature, the temperature of the high-temperature section is oscillated, and the saturated vapor pressure is adjusted. Firstly preserving heat for 7h at 1123K, then heating to 1143K for 1h, preserving heat for 20h, then cooling to 1123K for 7h after 1h, oscillating for 8 times in such a cycle, finally cooling to 373K after 17 h, turning off a power supply, cooling to room temperature along with the furnace, and finishing crystal growth. The heating procedure is shown in FIG. 5, and the resulting wafer is 170 μm thick, as shown in FIG. 6.
Example 2
The synthesized AgCrSe2Polycrystalline powder 1g and transmission medium CrCl 8mg3(7mg)+I2(1mg) mixing and evacuating to 10 deg.C- 4And Pa, sealing the tube, putting the tube into a double-temperature-zone tube furnace, and growing crystals according to a further improved gas phase transport method. The temperature of the high-temperature section is set to 1138K, the temperature of the low-temperature section is set to 1123K, the temperature is raised to the target temperature after 5 hours, then the low-temperature area keeps constant temperature, and the high-temperature area is subjected to temperature oscillation. Firstly, the temperature is maintained for 7 hours at 1138K, then the temperature is raised to 1173K and maintained for 10 hours after 0.5 hour, then the temperature is lowered to 1138K and maintained for 1 hour after 0.5 hour, then the temperature is raised to 1173K after 0.5 hour, the temperature is maintained for 11 hours, and therefore the last time of the once-circulation high-temperature platform heat-preservation time base is prolonged by 10 percent and the vibration is circulated for 10 times. Finally, the temperature is reduced to 373K after 17 hours, the power supply is turned off, and the temperature is cooled to room temperature along with the furnace, and the crystal growth is finished. The soak heating procedure is shown in FIG. 7, and the resulting wafer is 430 μm thick, as shown in FIG. 8.
Results and conclusions: prepared in examples 1 and 2Characteristic peak of XRD of wafer and AgCrSe in figure 92The characteristic peaks of the single crystal samples are completely consistent, which shows that AgCrSe is successfully prepared in examples 1 and 22A single crystal sample. Comparing example 1 with comparative example 1, it can be seen that the thickness of the finally prepared crystal can be significantly increased by adopting the oscillation heating process on the premise that the total time of the crystal growth is equivalent; comparing example 1 with example 2, it can be seen that, on the premise that the total crystal growth duration is equivalent, the number of oscillation periods is increased, and the heat preservation time of the high and low temperature platforms in the oscillation periods is gradually prolonged, so that the thickness of the finally prepared crystal can be further remarkably increased.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer 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, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A method for preparing anisotropic large-size crystals is characterized in that oscillation heating temperature curves are adopted for heating in the crystal growth process.
2. The method according to claim 1, wherein a horizontal dual-temperature zone vapor transport growth method is adopted in the crystal growth process, the dual-temperature zone comprises a low-temperature zone and a high-temperature zone, and at least one of the high-temperature zone and the low-temperature zone adopts an oscillating heating temperature curve.
3. 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) 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.
4. The method according to claim 3, wherein in step (1), the transport 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。
5. The method according to claim 3 or 4, wherein in the step (2), the dual-temperature zone comprises 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.
6. The method of claim 5, wherein step (2) satisfies at least one of the following conditions:
the step (2) is carried out in a horizontal double-temperature-zone tube furnace, the sealable container is a quartz crucible, and the diameter of the quartz crucible is 10-30 mm;
the temperature range of the low-temperature area is 750-870 ℃, and the temperature of the high-temperature area is 25-70 ℃ higher than that of the low-temperature area;
the oscillation heating temperature curve comprises at least one oscillation period, and each oscillation period independently comprises a low-temperature platform, a temperature rising section, a high-temperature platform and a temperature reducing section.
7. The method according to claim 6, wherein only the high temperature zone or only the low temperature zone adopts an oscillation heating temperature curve, the temperature oscillation amplitude of the oscillation heating temperature curve is 10-40 ℃, and each oscillation period is independently 1-40 h; or,
the high-temperature area and the low-temperature area adopt oscillation heating temperature curves at the same time, the temperature oscillation amplitude of the oscillation heating temperature curves of the high-temperature area and the low-temperature area is 5-20 ℃ respectively and independently, and each oscillation period is 1-40 h respectively and independently.
8. The method according to claim 6 or 7, characterized in that at least one of the following conditions is fulfilled:
the oscillation heating temperature curve comprises a plurality of oscillation periods, and 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;
the oscillation heating temperature curve comprises a plurality of oscillation cycles, and in at least two continuous oscillation cycles, at least one of the low-temperature platform time length, the heating-up section time length, the high-temperature platform time length and the cooling-down section time length of the next oscillation cycle is prolonged by 10-50% on the basis of the time length of the corresponding stage of the previous oscillation cycle;
the temperature gradient between the high-temperature area and the low-temperature area is 1-10 ℃/cm.
9. The method of claim 6, 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) the sealed container is placed in a high-temperature environment for annealing treatment,
optionally, in step (i), the purity of the elementary substance particles is not lower than 4N;
optionally, in the step (ii), the ball milling treatment time is 1-10 h;
optionally, in step (iii), directly evacuating to 10-4Pa and sealing; or, vacuumizing and filling inert gas, repeating for 3 times, and vacuumizing to 10-1Pa and sealing;
optionally, in the step (iv), the temperature of the annealing treatment is 450-800 ℃ and the time is 5-50 h.
10. The method of claim 6, 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;
(III) placing the sealed container in a high-temperature environment for annealing treatment,
optionally, in step (I), the purity of the elemental particles is not less than 4N;
optionally, in step (II), directly evacuating to 10-4Pa and sealing; or, vacuumizing and filling inert gas, repeating for 3 times, and vacuumizing to 10-1Pa and sealing;
optionally, in the step (III), the temperature of the annealing treatment is 600-900 ℃ and the time is 5-50 h.
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| CN105926030A (en) * | 2016-05-04 | 2016-09-07 | 南京安京太赫光电技术有限公司 | Method for growing large-size two-dimension material monocrystal through temperature wobble |
| WO2018023335A1 (en) * | 2016-08-01 | 2018-02-08 | 三和德盛（洛阳）蓝宝石晶体制造有限公司 | Method and apparatus for preparing sapphire crystal by moving temperature-field gradient |
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| US20130234375A1 (en) * | 2012-03-09 | 2013-09-12 | Zhifeng Ren | Methods of Synthesizing Thermoelectric Materials |
| WO2016123866A1 (en) * | 2015-02-05 | 2016-08-11 | 中国电子科技集团公司第二十六研究所 | Method for preparing large-sized slablike ce3+ ion doped rare-earth orthosilicate-series scintillation crystals by means of horizontal directional solidification |
| CN105926030A (en) * | 2016-05-04 | 2016-09-07 | 南京安京太赫光电技术有限公司 | Method for growing large-size two-dimension material monocrystal through temperature wobble |
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