CN115710744A - Large-size double perovskite structure single crystal material and preparation method thereof - Google Patents
Large-size double perovskite structure single crystal material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a large-size double perovskite structure single crystal material and a preparation method thereof, belonging to the technical field of perovskite single crystal materials, and the structural general formula is AB 1 B 2 X, wherein A is selected from Na, K, rb, cs and Ca; b is 1 Selected from Ag, in, sb, sn, li, cu, ni, pd, pt; b is 2 Selected from Bi, pb, S, Y, la, fe, zn; x is selected from Cl, br and I, and the preparation method comprises the following steps: putting raw materials for forming the double perovskite structure crystal into a quartz bottle subjected to vacuum sintering, and heating the quartz bottle in a high-temperature region of a Bridgman furnace to obtain a eutectic body; slowly moving the eutectic body along the longitudinal axis direction to a low-temperature region below the melting point of the eutectic body, solidifying and crystallizing the eutectic body, and slowly cooling toAt room temperature, the prepared double perovskite structure type crystal has the characteristics of large size, high hardness and few defects, and is convenient to process and use for photoelectric devices and the like.
Description
Technical Field
The invention relates to the technical field of perovskite single crystal materials, in particular to a large-size double perovskite structure single crystal material and a preparation method thereof.
Background
The double perovskite material has a structural general formula AB 1 B 2 And (4) X. Wherein A is selected from Na, K, rb, cs, ca and other elements, B 1 Selected from Ag, in, sb, sn, li, cu, ni, pd, pt and other elements, B 2 Elements selected from Bi, pb, S, Y, la, fe, zn and the like, and X is selected from halogen elements such as Cl, br, I and the like; in recent years, double perovskite materials are widely applied in the fields of solar cells, light emitting diodes, photodetectors and the like. The metal halide material has the advantages of low cost, high photoelectric conversion efficiency and the like. AB compared to conventional perovskite materials 1 B 2 The X can reduce the use of toxic elements such as Pb and the like while realizing the photoelectric property, protects the environment, has higher stability and is a hotspot research object in the field of photoelectric materials.
With the development of the electronics and semiconductor industries, there is an increasing demand for semiconductor single crystals that are large in size, can be sliced and polished, and can be used for manufacturing substrates. The Bridgman method for single crystal growth has the characteristics of low defect density, large volume and the like, and is a potential production method for preparing substrates in the semiconductor industry. For some time recently, there have also been some reports on the use of the bridgman method for the preparation of perovskite single crystals.
In 2021, the Chinese academy of sciences reported that Cs grew using the Bridgman method 3 Cu 2 I 5 Bulk crystals, a type of latent scintillator that can be used for x-ray and gamma-ray detection. Similarly, in 2021, shandong university in the literature "Li X, du X, zhang P, et al 3 Bi 2 Br 9 single crystals for high-performance X-ray detection[J]Science China Materials,2021,64 (6): 1427-1436, "reports the use of the Bridgman method to grow Cs 3 Bi 2 Br 9 Large-volume single crystal with diameter of 12mm and length of 40mm, transparency, no crack, and defect density of only 9.7 × 10 10 cm -3 The method can be applied to the fields of photoelectric detectors, X-ray imaging and the like.
The current literature reports that perovskite materials with an ABX (A and B are metal elements, and X is a halogen element) structural general formula are prepared only by using a Bridgman method, and the perovskite materials have the defects of large temperature fluctuation, easy generation of polycrystal, poor transparency and the like. The large-size double perovskite structure single crystal material has great potential in semiconductor processing and application, but the method for preparing the large-size double perovskite structure single crystal by using the Bridgman method has not been reported.
Disclosure of Invention
The present invention has an object to provide a large-sized double perovskite structure single crystal material, and another object to provide a method for producing such a large-sized perovskite structure single crystal material, which enables the single crystal to be successfully produced using the Bridgman method.
In order to achieve the purpose, the invention provides the following scheme:
the invention provides a preparation method of a large-size double perovskite structure single crystal material, which comprises the following steps:
1) Selecting high-purity raw materials with corresponding mass according to the atomic ratio of the molecular formula of the expected product, uniformly mixing, grinding by using a mortar, and placing in a quartz tube with a circle of concave on the tube wall;
2) Placing a quartz column with a diameter slightly smaller than the inner diameter of the quartz tube to clamp the quartz column at the recessed position, and pumping the gas pressure in the quartz tube to a value lower than 1 × 10 by using a molecular pump -3 Pa；
3) Sintering the quartz tube along the recessed position, preferably by using a hydrogen-oxygen water welding machine;
4) Operating a Bridgman furnace having at least two temperature zones, wherein the temperature of the higher temperature zone is set slightly above the melting point of the desired product and the temperature of the lower temperature zone is set below the melting point of the desired product;
5) Placing the quartz tube in a high-temperature region of a Bridgman furnace, and slowly increasing the high-temperature region and the low-temperature region of the Bridgman furnace from room temperature to a target temperature;
6) Keeping the quartz tube at the position after the quartz tube reaches the preset temperature in the high-temperature area, and preserving the heat for 8-24h at the temperature; heating the sintered mixture in a high-temperature area above a Bridgman furnace to obtain a eutectic body;
7) The quartz tube slowly and vertically moves from a high-temperature area to a low-temperature area of the Bridgman furnace at a certain speed, the step is a directional solidification process, the aim is to enable the eutectic to pass through a melting point and undergo a process of solidification and crystallization from bottom to top, a solid-liquid interface is a convex interface or a flat interface when the eutectic moves to the low-temperature area lower than the melting point in the directional solidification process, and the average temperature gradient is higher than 10 ℃/cm and lower than 60 ℃/cm;
8) After the quartz tube is vertically lowered to a position lower than the melting point temperature of the expected product, slowly lowering the Bridgman furnace to the room temperature;
9) And taking out the quartz tube, carefully knocking the quartz tube apart along the depression for sintering, and taking out the single crystal inside, namely the large-size double perovskite structure single crystal material.
The preparation method comprises the following steps: a heating and melting process, namely placing the raw materials forming the double perovskite structure crystal into a quartz bottle subjected to vacuum sintering, and heating the raw materials in a high-temperature region above a Bridgman furnace to obtain a eutectic body; a directional solidification process, namely, the obtained eutectic slowly moves downwards along the longitudinal axis direction to a low-temperature region lower than the melting point of the eutectic, so that the eutectic undergoes a solidification crystallization process from bottom to top; and a slow cooling process, namely slowly cooling the large-size crystal with the double perovskite structure to room temperature. The prepared double perovskite structure type crystal has the characteristics of large size, high hardness and few defects, and is convenient to process and use in photoelectric devices and the like.
Preferably, the melting point of the large-sized double perovskite structure single crystal material is 400 ℃ or more and less than 620 ℃.
Preferably, in the step 1), the wall thickness of the quartz tube is 0.5-2mm, preferably 1mm, the upper part of the quartz tube is a hollow cylinder, and the bottom of the quartz tube is a round bottom or a pointed bottom with a cone angle of 20-120 degrees; when a quartz tube with an angle at the bottom is used, the wall thickness is more than 1mm, and the output power of the oxyhydrogen water welding machine is more than 288W; the purity of the high-purity raw material is 4N or more.
Preferably, in step 4), the temperature of the high temperature zone is set to 10 to 150 ℃ higher than the melting point of the desired product, and the temperature of the low temperature zone is set to 10 to 200 ℃ lower than the melting point of the desired product. The large temperature gradient, although the nucleation driving force is strong, easily causes crystal cracking, so when growing a large-volume single crystal, the temperature gradient needs to be precisely controlled.
Preferably, in the step 4), a material with low thermal conductivity, such as mica or aluminum silicate, is placed between the high-temperature region and the low-temperature region of the Bridgman furnace, so that the thermal conductivity between the high-temperature region and the low-temperature region is adjusted, and the temperature gradient is adjusted.
Preferably, in the step 5), the average temperature rise rate of the high-low temperature region of the Bridgman furnace is 30-80 ℃/h.
Preferably, in step 7), the average moving rate of the vertical movement of the quartz tube is 0.1 to 4mm/h, and the average moving rate of the vertical falling is preferably 0.1 to 0.5mm/h.
Preferably, in the step 8), the average temperature reduction rate of the Bridgman furnace is 20-80 ℃/h.
Preferably, in step 9), after taking out the single crystal, checking the obtained crystal (complete shape and no crack on the surface), and if the obtained crystal is accompanied by impurity precipitation, repeating the steps 4) to 8) to purify and remove the precipitated impurity; in the purification process, the vertical descending average moving speed of the quartz tube in the step 7) is 0.5-4mm/h.
The large-size double perovskite structure single crystal material prepared by the preparation method has a structural general formula of AB 1 B 2 X, wherein A is selected from Na, K, rb, cs and Ca; b 1 Selected from Ag, in, sb, sn, li, cu, ni, pd, pt; b is 2 Selected from Bi, pb, S, Y, la, fe, zn; x is selected from Cl, br and I.
The invention discloses the following technical effects:
the raw material powder is put into a quartz tube and sintered under a high vacuum condition, so that the raw material powder is prevented from reacting with air components at a high temperature to cause crystal defects, and the quality of crystals is improved.
The Bridgman furnace adopts a tubular hearth and is provided with at least two temperature zones. Wherein the temperature of the high temperature region is higher than the melting point of the eutectic, and the temperature of the low temperature region is lower than the melting point of the eutectic, so that a temperature gradient which is reduced from the melting point higher than the eutectic to the melting point lower than the eutectic is generated between the high temperature region and the low temperature region. When the quartz tube is heated and insulated in the high-temperature region and is fully melted, the quartz tube slowly moves vertically to the low-temperature region, and the eutectic body undergoes the crystallization process from bottom to top.
When the quartz tube with the bottom at a specific angle is adopted, only a single crystal nucleus has enough space to grow upwards according to the geometric elimination rule to form a single crystal. This process effectively avoids crystal cracking. In addition, when the temperature gradient between the high temperature region and the low temperature region is larger, the segregation effect can be fully utilized to enrich the impurities into the melt due to the fact that the solubility of the impurities in the solid phase is different from that of the impurities in the liquid phase. Therefore, under the condition of large temperature gradient, the directional solidification process is repeated, so that the purification effect can be achieved, the crystal defects are reduced, and the transparency is improved. In addition, the melt is excessively cooled due to the excessively high reduction speed, so that crystals are not directional and cracked, and the crystallization quality can be effectively improved due to the adoption of the low reduction speed after purification.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic diagram of a method for preparing a large-sized single crystal material with a double perovskite structure according to the present invention;
FIG. 2 shows Cs obtained by the temperature-decreasing crystallization method of comparative example 1 2 AgBiBr 6 Comparing a single crystal powder X-ray diffraction pattern (XRD) with an X-ray powder diffraction pattern obtained by simulation calculation;
FIG. 3 shows large-size Cs obtained by the Bridgman method in example 1 2 AgBiBr 6 Comparing a single crystal powder X-ray diffraction pattern (XRD) with an X-ray powder diffraction pattern obtained by simulation calculation;
FIG. 4 shows large-size Cs obtained by the Bridgman method in example 1 2 AgBiBr 6 Schematic diagram of single crystal unit cell structure.
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in the present disclosure, it is understood that each intervening value, to the upper and lower limit of that range, is also specifically disclosed. Every intervening value, to the extent any stated or intervening value in a stated range, and every other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
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 to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the documents are cited. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. It is intended that the specification and examples be considered as exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.
The room temperature in the present invention means 25. + -. 2 ℃.
The schematic diagram of the preparation method of the large-size double perovskite structure single crystal material is shown in figure 1.
Comparative example 1 preparation of Cs 2 AgBiBr 6 Perovskite single crystal (use ofWidely reported cooling crystallization method
1) Solution preparation
The method comprises the following specific steps: 0.0852g CsBr powder, 0.0376g AgBr powder and 0.0916g BiBr powder were mixed and dissolved in 2mL HBr and heated at 150 ℃ for 5h until the solution was sufficiently dissolved.
2) Crystal growth
The resulting solution was cooled to 110 ℃ at a rate of 2 ℃/h and crystal nucleation was observed. Adjusting the cooling rate to 1 ℃/h, cooling to 60 ℃, and keeping at 60 ℃ for 5 hours to ensure that the crystal basically finishes growing. Adjusting the cooling rate to 5 ℃/h, and cooling to room temperature. The obtained crystal was taken out using tweezers, washed and dried. Cs obtained by cooling crystallization 2 AgBiBr 6 The perovskite single crystal has a maximum dimension of only about 0.2cm x 0.15cm.
After the single crystal is prepared, the single crystal is subjected to X-ray powder diffraction test, and Cs prepared by a cooling crystallization method 2 AgBiBr 6 The single crystal powder X-ray diffraction pattern (XRD) is compared to the X-ray powder diffraction pattern calculated by simulation, as shown in fig. 2. The test angle range (2 θ) is 20 ° -45 °, the interval between adjacent scan points is 0.02 °, the dwell time on each scan point is 0.1s, and the peaks corresponding to the (220), (222) and (400) crystallographic planes are found at 2 θ =22.25 °,2 θ =27.37 ° and 2 θ =31.68 °, respectively.
EXAMPLE 1 preparation of Cs of Large size by the Bridgman method 2 AgBiBr 6 Perovskite single crystal
1) Preparation of raw materials
The method comprises the following specific steps: 3.7280g CsBr powder, 1.6447g AgBr powder and 4.0062g BiBr 3 The powders were mixed homogeneously and placed in a quartz tube having a wall thickness of 1 mm. The pipe wall of the quartz pipe is provided with a circle of recess, which is convenient for subsequent welding and sealing. The bottom of the quartz tube is provided with a sharp corner with an angle of 40 degrees.
2) Vacuum sealing tube
And (5) placing the quartz column with the inner diameter slightly smaller than the inner diameter of the quartz tube, and clamping the quartz column at the concave position. Reducing the gas pressure in the quartz tube to 1 × 10 by using a molecular pump -3 After Pa is less than Pa, the quartz tube is sintered along the concave position by using a hydrogen-oxygen water welding machine. The output power of the oxyhydrogen water welding machine is378W。
3) Synthesis of polycrystalline Material
The resulting quartz tube was placed in a bridgeman furnace. The quartz tube was positioned from room temperature over 6h to 460 ℃ and incubated at 460 ℃ for 12h and finally cooled to room temperature over 8h. The quartz tube was removed, carefully broken and the quality of the polycrystalline material obtained was checked.
4) Heating and melting
And (5) repeating the step 2) to sinter the quartz tube in vacuum.
The arrangement of a high-temperature region and a low-temperature region of the Bridgman furnace is regulated, two layers of heat insulation rings made of mica materials are added in the high-temperature region and the low-temperature region, the heat insulation rings are concentric rings with the outer diameter of 8cm, the inner diameter of 6cm and the height of 1cm, and the thermal conductivity of the heat insulation rings is 0.15W/mk. The temperature in the furnace can be gradually transited from 480 ℃ to 350 ℃ after being regulated, and the average temperature gradient is about 25 ℃/cm.
The quartz tube was placed in the high temperature zone of the bridgeman furnace at 480 ℃. The bridgeman furnace was started and after 8h the above process conditions were reached.
The quartz tube is kept at 480 ℃ for 12h in the Bridgman furnace.
5) Directional solidification
The quartz tube is kept at 480 ℃ for 12 hours in a Bridgman furnace and then slowly moves to 350 ℃ at the speed of 0.5mm/h, and in the process, the polycrystalline material undergoes a recrystallization process from bottom to top in the quartz tube. The angle of the bottom of the quartz tube plays a role in geometric elimination of a plurality of crystal nuclei.
6) Slowly cool down
After the quartz tube reaches the 350 ℃ position of the low-temperature zone of the Bridgman furnace, the temperature is slowly reduced to the room temperature for 24 hours.
7) Checking the quality of the crystals
Taking out the quartz tube, carefully knocking the quartz tube open along the recess for sintering, and taking out the Cs therein 2 AgBiBr 6 Single crystal, detecting the product. Cs obtained by the Bridgman method 2 AgBiBr 6 The diameter of the single crystal is about 1.2cm, the length of the single crystal is about 15cm, and the size of the single crystal is far larger than that of Cs obtained by the cooling crystallization method in comparative example 1 2 AgBiBr 6 And (3) single crystal.
After the single crystal is prepared, the method is carried outX-ray powder diffraction measurements were performed. Large-size Cs prepared by Bridgman method 2 AgBiBr 6 The single crystal powder X-ray diffraction pattern (XRD) is compared to the X-ray powder diffraction pattern calculated by simulation, as shown in fig. 3. The test angle range (2 θ) is 20 ° -45 °, the interval between adjacent scan points is 0.02 °, the dwell time on each scan point is 0.1s, and the peaks corresponding to the (220), (222) and (400) crystallographic planes are found at 2 θ =22.29 °,2 θ =27.28 ° and 2 θ =31.84 °, respectively. The crystal obtained by using SHELX and OLEX2.35 is subjected to structural analysis and modification, and can be obtained as belonging to Fm-3m (cubic) space group, wherein
α = β = γ =90 °, cell volume of
Atoms occupy the following Wyckoff positions: cs:8c (0.25, 0.75); ag:4b (0.5 ); bi:4a (0, 0.5); br:24e (0.25082, 0.5), a schematic of the crystal structure, as shown in FIG. 4. Crystallographic parameters obtained using SHELX and OLEX2.35, as shown in table 1; cs 2 AgBiBr 6 The single crystal has an indirect band gap of 1.95eV, has complete appearance, no cracks on the surface and no impurities, is applied to a photoelectric detector, and has the characteristics of high detection rate and high responsivity.
TABLE 1
Example 2 Bridgman method for preparing voluminous Rb 2 AgBiI 6 Perovskite single crystal
1) Preparation of raw materials
The method comprises the following specific steps: 5.3093g of RbI powder, 2.9346g of AgI powder and 7.3711g of BiI powder 3 The powders were mixed homogeneously and placed in a quartz tube having a wall thickness of 1 mm. The pipe wall of the quartz pipe is provided with a circle of concave parts, so that the subsequent sealing is convenient.
2) Vacuum sealing tube
Put into a quartz tube with the inner diameter slightly smaller than that of the quartz tubeThe quartz column with the diameter is clamped in the concave position. Reducing the gas pressure in the quartz tube to 1 × 10 by using a molecular pump -4 And after Pa, sintering the quartz tube along the concave position by using a hydrogen-oxygen water welding machine. The output power of the oxyhydrogen water welding machine is 378W.
3) Synthesis of polycrystalline Material
The resulting quartz tube was placed in a bridgeman furnace. The quartz tube was positioned from room temperature to 470 ℃ over 8h, and was kept at 470 ℃ for 12h, and finally cooled to room temperature over 12h. The quartz tube was removed, carefully broken and the quality of the polycrystalline material obtained was checked.
4) Heating and melting
And (5) repeating the step 2) to sinter the quartz tube in vacuum.
The arrangement of a high-temperature region and a low-temperature region of the Bridgman furnace is regulated and controlled, three layers of heat insulation rings made of mica materials are added in the high-temperature region and the low-temperature region, the heat insulation rings are concentric rings with the outer diameter of 8cm, the inner diameter of 6cm and the height of 1cm, and the thermal conductivity of the heat insulation rings is 0.15W/mk. The temperature in the furnace can be gradually transited from 490 ℃ to 300 ℃ after regulation, and the average temperature gradient is about 35 ℃/cm.
The quartz tube was placed in the high temperature region 490 c of the bridgeman furnace. The bridgeman furnace was started and after 12h the above process conditions were reached.
The quartz tube is kept at 490 ℃ for 16h in the Bridgman furnace.
5) Directional solidification
The quartz tube was held at 490 ℃ for 16 hours in a Bridgman furnace and then slowly moved at a rate of 1mm/h to a 300 ℃ region, during which the polycrystalline material underwent a bottom-up recrystallization process in the quartz tube. The angle of the bottom of the quartz tube plays a role in geometric elimination of a plurality of crystal nuclei.
6) Slowly cool down
After the quartz tube reaches the 300 ℃ position of the low-temperature zone of the Bridgman furnace, the temperature is slowly reduced to the room temperature after 36 hours.
7) Checking the quality of the crystals
Taking out the quartz tube, carefully knocking the quartz tube apart along the recess for sintering, and taking out Rb in the quartz tube 2 AgBiI 6 Single crystal, detecting the product, the obtained product has complete shape, no crack on the surface and no impurity。
Rb 2 AgBiI 6 The optical band gap of the optical band gap is 1.98eV, and the optical band gap has wide potential of being applied to photoelectric devices.
Example 3 Bridgman method for preparing bulky Cs 2 AgInCl 6 Perovskite single crystal
1) Preparation of raw materials
The method comprises the following specific steps: 4.2090g CsCl powder, 1.7915g AgCl powder and 2.7648g InCl 3 The powders were mixed homogeneously and placed in a quartz tube with a wall thickness of 0.5 mm. The pipe wall of the quartz pipe is provided with a circle of concave parts, so that subsequent sealing is facilitated.
2) Vacuum sealing tube
And (5) placing the quartz column with the inner diameter slightly smaller than the inner diameter of the quartz tube, and clamping the quartz column at the concave position. Reducing the gas pressure in the quartz tube to 1x10 using a molecular pump -4 And after Pa, sintering the quartz tube along the concave position by using a hydrogen-oxygen water welding machine. The output power of the oxyhydrogen water welding machine is 288W.
3) Synthesis of polycrystalline Material
The resulting quartz tube was placed in a Bridgman furnace. The quartz tube was positioned from room temperature to 565 ℃ over 8h, and incubated at 565 ℃ for 12h and finally cooled to room temperature over 6h. The quartz tube was removed, carefully broken and the quality of the polycrystalline material obtained was checked.
8) Heating and melting
And (5) repeating the step 2) to sinter the quartz tube in vacuum.
The arrangement of a high-temperature region and a low-temperature region of the Bridgman furnace is regulated, a layer of heat insulation ring made of mica material is added in the high-temperature region and the low-temperature region, the heat insulation ring is a concentric ring with the outer diameter of 8cm, the inner diameter of 6cm and the height of 1cm, and the thermal conductivity of the concentric ring is 0.15W/mk. The temperature in the furnace can be gradually transited from 580 ℃ to 450 ℃ after being regulated, and the average temperature gradient is about 20 ℃/cm.
The quartz tube was placed in the high temperature zone of the Bridgman furnace at 580 ℃. The bridgeman furnace was started and after 18h the above process conditions were reached.
The quartz tube is kept at 580 ℃ for 18h in the Bridgman furnace.
9) Directional solidification
The quartz tube was held at 580 ℃ for 18 hours in a Bridgman furnace and then slowly moved at a rate of 0.1mm/h to a 450 ℃ region, during which the polycrystalline material underwent a bottom-up recrystallization process in the quartz tube. The angle of the bottom of the quartz tube plays a role in geometric elimination of a plurality of crystal nuclei.
10 Slow cooling
After the quartz tube reaches the 450 ℃ position of the low-temperature zone of the Bridgman furnace, the temperature is slowly reduced to the room temperature after 36 hours.
11 Checking the quality of the crystal
Taking out the quartz tube, carefully knocking the quartz tube open along the recess for sintering, and taking out the Cs therein 2 AgInCl 6 And (3) single-crystallizing, detecting the product, wherein the obtained product has no impurities, complete appearance and no cracks on the surface.
Comparative example 2
Preparation of raw materials
The method comprises the following specific steps: 3.7280g CsBr powder, 1.6447g AgBr powder and 4.0062g BiBr 3 The powders were mixed homogeneously and placed in a quartz tube having a wall thickness of 1 mm. The pipe wall of the quartz pipe is provided with a circle of concave, which is convenient for subsequent welding and sealing. The bottom of the quartz tube is provided with a sharp corner with an angle of 40 degrees.
1) Vacuum sealing tube
And (4) placing the quartz column with the inner diameter slightly smaller than the inner diameter of the quartz tube, and clamping the quartz column at the concave position. Reducing the gas pressure in the quartz tube to 1 × 10 by using a molecular pump -3 After Pa is less than Pa, the quartz tube is sintered along the concave position by using a hydrogen-oxygen water welding machine. The output power of the oxyhydrogen water welding machine is 378W.
2) Synthesis of polycrystalline Material
The resulting quartz tube was placed in a bridgeman furnace. The quartz tube was positioned from room temperature over 6h to 460 ℃ and incubated at 460 ℃ for 12h and finally cooled to room temperature over 8h. The quartz tube was removed, carefully broken and the quality of the polycrystalline material obtained was checked.
3) Heating and melting
And (3) repeating the step 2) to sinter the quartz tube in vacuum.
The arrangement of a high-temperature and low-temperature region of the Bridgman furnace is regulated and controlled, two layers of heat insulation rings made of mica materials are added in the high-temperature and low-temperature region, the heat insulation rings are concentric rings with the outer diameter of 8cm, the inner diameter of 6cm and the height of 1cm, and the thermal conductivity of the heat insulation rings is 0.15W/mk. The regulated temperature in the furnace can be gradually transited from 480 ℃ to 350 ℃, and the average temperature gradient is about 20 ℃/cm.
The quartz tube was placed in the high temperature zone of the bridgeman furnace at 480 ℃. The bridgeman furnace was started and after 8h the above process conditions were reached.
The quartz tube is kept at 480 ℃ for 12h in the Bridgman furnace.
4) Directional solidification
The quartz tube was kept at 480 ℃ for 12 hours in a Bridgman furnace and then moved to 350 ℃ at a rate of 3mm/h, during which the polycrystalline material underwent a recrystallization process from bottom to top in the quartz tube. The angle of the bottom of the quartz tube plays a role in geometric elimination of a plurality of crystal nuclei.
5) Slowly cool down
After the quartz tube reaches the 350 ℃ position of the low-temperature zone of the Bridgman furnace, the temperature is slowly reduced to the room temperature for 24 hours.
6) Checking the quality of the crystals
Taking out the quartz tube, carefully knocking the quartz tube apart along the depression for sintering, and taking out the Cs therein 2 AgBiBr 6 And (5) crystals are detected. The cracking of the crystal is serious, and the quality of the crystal is not good. The reason for this is that the drop rate is selected too fast and the melt is supercooled rapidly at multiple locations, resulting in inconsistent orientation of the crystals and ultimately in cracking and inhomogeneity of the crystals.
As can be seen from example 1 and comparative example 2, cs grows at an excessively fast fall rate 2 AgBiBr 6 It causes severe cracking of the crystals.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (8)
1. A preparation method of a large-size double perovskite structure single crystal material is characterized by comprising the following steps:
1) Selecting high-purity raw materials with corresponding mass according to the atomic ratio of the molecular formula of the expected product, uniformly mixing, grinding, and placing in a quartz tube with a circle of concave on the tube wall;
2) Placing a quartz column with a diameter slightly smaller than the inner diameter of the ampere tube of the quartz tube to be clamped at the concave position, and pumping the air pressure in the quartz tube to be lower than 1 × 10 -3 Pa；
3) Sintering the quartz tube along the recessed position;
4) Operating a Bridgman furnace having at least two temperature zones, wherein the temperature of the high temperature zone is set slightly above the melting point of the desired product and the temperature of the low temperature zone is set below the melting point of the desired product;
5) Placing the quartz tube in a high-temperature region of a Bridgman furnace, and raising the high-temperature region and the low-temperature region of the Bridgman furnace from room temperature to a target temperature;
6) Keeping the quartz tube at the position after the quartz tube reaches the preset temperature in the high-temperature area, and preserving the heat for 8-24 hours at the temperature;
7) The quartz tube vertically moves from a high-temperature area to a low-temperature area of the Bridgman furnace at a certain speed;
8) After the quartz tube is vertically lowered to a position below the melting point temperature of the desired product, the Bridgman furnace is lowered to room temperature;
9) And taking out the quartz tube, carefully knocking the quartz tube apart along the depression for sintering, and taking out the single crystal inside, namely the large-size double perovskite structure single crystal material.
2. The production method according to claim 1, wherein in step 1), the wall thickness of the quartz tube is 1mm; the purity of the high-purity raw material is more than 4N.
3. The method of claim 1, wherein in the step 4), the temperature of the high temperature region is set to 10 to 150 ℃ higher than the melting point of the desired product, and the temperature of the low temperature region is set to 10 to 200 ℃ lower than the melting point of the desired product.
4. The method as claimed in claim 1, wherein mica or aluminum silicate is placed between the high and low temperature regions of the Bridgman furnace in the step 4).
5. The method according to claim 1, wherein in the step 5), the average temperature rise rate in the high and low temperature regions of the Bridgman furnace is 30-80 ℃/h.
6. The production method according to claim 1, wherein in the step 7), the average moving speed of the vertical movement of the quartz tube is 0.1 to 4mm/h.
7. The method according to claim 1, wherein in step 8), the average temperature reduction rate of the Bridgman furnace is 20-80 ℃/h.
8. A large-sized single crystal material with a double perovskite structure prepared by the preparation method according to any one of claims 1 to 7, wherein the structural formula is AB 1 B 2 X, wherein A is selected from Na, K, rb, cs and Ca; b 1 Selected from Ag, in, sb, sn, li, cu, ni, pd, pt; b is 2 Selected from Bi, pb, S, Y, la, fe, zn; x is selected from Cl, br and I.
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