Strontium lanthanum tantalate aluminate bicrystal seed crystal and preparation method of crystal of strontium lanthanum tantalate aluminate bicrystal seed crystal

Abstract

The invention relates to the technical field of bicrystal substrates, and particularly discloses a preparation method of a strontium lanthanum tantalum aluminate bicrystal seed crystal, which comprises the following steps: preparing a first strontium lanthanum tantalum aluminate bicrystal crystal base material by using a sintering method, cutting a crystal blank with an intact crystal boundary from the first strontium lanthanum tantalum aluminate bicrystal crystal base material, and carrying out rough polishing, chemical polishing and ion beam polishing to obtain a first bicrystal seed crystal; preparing a large-size or small-size second strontium lanthanum tantalate aluminate bicrystal crystal base material from the first bicrystal seed crystal by using a pulling method, and cutting a crystal blank from the second strontium lanthanum tantalate aluminate bicrystal crystal base material to obtain the strontium lanthanum tantalate aluminate bicrystal seed crystal. The preparation method comprises the following steps: preparing a first strontium lanthanum tantalate aluminate bicrystal crystal base material by using a sintering method, cutting a crystal blank with an intact crystal boundary from the first strontium lanthanum tantalate aluminate bicrystal crystal base material by using diamond wire cutting to serve as a first bicrystal seed crystal, preparing a large-size strontium lanthanum tantalate aluminate bicrystal crystal by using a pulling method, and cutting the crystal blank from the large-size strontium lanthanum tantalate aluminate bicrystal crystal to serve as a seed crystal of a subsequent growth crystal; the crystal boundary of the grown bicrystal crystal is naturally closed, and the bicrystal crystal is free of voids, defects and external dust particle pollution and is compact and uniform in structure.

Description

Technical Field

[0001] The present invention relates to the technical field of twin crystal substrates, and in particular to a strontium lanthanum tantalate aluminate twin crystal seed crystal and a preparation method of the crystal. Background Art

[0002] The lattice constant of lanthanum strontium aluminate tantalate (LSAT) crystal is close to that of high-temperature superconducting thin film material yttrium barium copper oxide (YBCO), and the lattice match is good. Therefore, it is often used as the substrate material for growing and preparing high-temperature superconducting thin film material yttrium barium copper oxide (YBCO).

[0003] Yttrium barium copper oxide (YBCO), a high-temperature superconducting thin film material, is a key material for high-temperature superconducting quantum interference devices (HT-SQUIDs). YBCO is grown on a lanthanum strontium aluminate (LSAT) bicrystalline substrate using physical deposition (pulsed laser deposition, PLD, magnetron sputtering, etc.) or chemical deposition (MOCVD, etc.). Therefore, the quality of the LSAT bicrystalline substrate affects the quality of the YBCO high-temperature superconducting thin film, and thus the performance of the HT-SQUID. Currently, lanthanum strontium aluminate tantalate (LSAT) bi-crystal substrates for fabricating yttrium barium copper oxide (YBCO) high-temperature superconducting thin films are mostly produced using a sintering method. This process involves first preparing a single crystal of lanthanum strontium aluminate (LSAT) material, then determining the angle and size of the twin grain boundary. The LSAT is then cut, ground, and polished. Two LSAT ingots are then bonded together and sintered at high temperature using a hot press. During the preparation of these LSAT bi-crystal substrates, the bonding process often takes place in a non-vacuum, low-grade cleanroom environment. This process inevitably introduces dust particles, contaminating the grain boundaries and causing defects such as grain boundary discontinuities. This significantly reduces the yield of the finished YBCO bi-crystal high-temperature superconducting thin film. Therefore, it is necessary to find a method to improve the quality of the LSAT twin grain boundaries. Summary of the Invention

[0004] In view of the above shortcomings, the present invention provides a method for preparing a strontium lanthanum tantalate twinned seed crystal and its crystal. The prepared twinned crystal has naturally closed grain boundaries, no voids, no defects, no external dust particle pollution, and a dense and uniform structure. The specific technical solution is as follows:

[0005] A strontium lanthanum tantalate twinned seed crystal is prepared by the following method: first, a first strontium lanthanum tantalate twinned crystal mother material is prepared by a sintering method, a rectangular solid crystal blank with intact grain boundaries is cut out from the mother material, and the blank is used as a first twinned seed crystal after rough polishing, chemical polishing, and ion beam polishing; a large-sized or small-sized second strontium lanthanum tantalate twinned crystal mother material is prepared from the first twinned seed crystal by a Czochralski method, and a rectangular solid crystal blank is cut out from the second strontium lanthanum tantalate twinned crystal mother material to obtain the strontium lanthanum tantalate twinned seed crystal.

[0006] On the other hand, the present invention also provides a method for preparing the above-mentioned strontium lanthanum tantalate aluminate twinned seed crystal, comprising the following steps:

[0007] (1) preparing a first twinned crystal base material of strontium lanthanum aluminate tantalate by sintering, and cutting it by diamond wire cutting at a cutting speed of 0.1 to 1 mm / min to obtain a contamination-free rectangular solid crystal blank with uniform grain boundaries and grain boundary line widths in the nanometer scale as the first twinned seed crystal;

[0008] (2) The first twin crystal seed crystal is subjected to surface treatment, which includes rough polishing, chemical polishing, and ion beam polishing to obtain the treated first twin crystal seed crystal. The outer dimension error of the treated first twin crystal seed crystal is required to be ±0.01 mm, and the surface roughness is

[0009]

[0010] (3) placing the first twinned seed crystal into a pulling device, and performing twinned growth by pulling in an oxygen atmosphere to obtain a second strontium lanthanum tantalate aluminum twinned crystal mother material;

[0011] (4) Cutting the second strontium lanthanum aluminate twin crystal mother material obtained in step (3) into a cubic crystal blank with uniform grain boundaries and grain boundary line widths at the nanometer scale to obtain a strontium lanthanum aluminate twin crystal seed crystal for preparing a strontium lanthanum aluminate twin crystal.

[0012] Preferably, in the above-mentioned method for preparing lanthanum strontium aluminate tantalate twinned seed crystals, the lanthanum strontium aluminate tantalate (LSAT) twinned mother material requires: crystal purity ≥ 99.9999%, no twins, and no bubbles.

[0013] Preferably, in the above-mentioned method for preparing strontium lanthanum tantalate aluminate twinned seed crystals, the first twinned seed crystals and the strontium lanthanum tantalate aluminate twinned seed crystals are rectangular parallelepipeds with dimensions of 3-5 mm×3-5 mm×5-10 mm.

[0014] Preferably, in the above-mentioned method for preparing strontium lanthanum tantalate aluminate twinned seed crystals, the twinned grain boundary angle is 6°, 12°, 18°, 24°, 30° or 36°.

[0015] Preferably, in the above-mentioned method for preparing lanthanum strontium aluminate twinned seed crystals, the pulling device includes a furnace body, a furnace cover, and a growth system. The furnace cover is removably and sealedly mounted above the furnace body. The growth system is located inside the furnace body and includes a crucible. The bottom of the crucible is provided with a base, an induction heating coil is provided on the outer wall of the crucible, an insulation layer is provided around the crucible, a pulling rod is suspended above the crucible, and the pulling rod can move up and down and rotate. The furnace cover is provided with an air inlet and an air inlet valve, and the bottom of the furnace body is provided with an exhaust port and an exhaust valve. The base is adjustable to adjust the height of the crucible to cooperate with the crystal pulling operation and adapt to various crucible models. A thermal insulation layer is added around the crucible to ensure a uniform temperature field.

[0016] Preferably, in the above-mentioned preparation method of lanthanum strontium aluminate twinned seed crystal, the twinned crystal pulling and growing process includes: placing the lanthanum strontium aluminate raw material into the bottom of the crucible, sealing the pulling device, heating through the induction coil, completely melting the raw material, and when the melt flow line is clear and stable, slowly lowering the seed crystal from the side containing the grain boundary in the seed crystal, and after the seed crystal contacts the melt surface, adjusting the furnace temperature to 1500-1700°C, the oxygen pressure to 1-5atm, the pulling speed to 1-3mm / h and the rotation speed to 15-25rpm, and pulling and growing the twinned crystal. In order to ensure the uniformity, defect-freeness and crystal quality of the pulled twin crystal boundaries, it is necessary to ensure the thermodynamic and kinetic balance at the grain boundaries, that is, by reducing the heating power in the early stage of grain boundary formation to reduce the disturbance of the melt convection on the interface; by appropriately reducing the pulling speed to reduce the stress accumulation at the grain boundary; by appropriately increasing the rotation speed to optimize the melt convection and promote uniform mixing of the melt on both sides of the grain boundary, so as to ensure the uniformity of the grain boundary, reduce defects and improve the crystal quality.

[0017] Preferably, in the above-mentioned method for preparing strontium lanthanum tantalate aluminate twinned seed crystals, the furnace temperature is 1500-1700°C, the oxygen pressure is 1-5 atm, the pulling speed is 1-3 mm / h and the rotation speed is 15-25 rpm.

[0018] Preferably, in the above-mentioned method for preparing lanthanum strontium aluminate twinned seed crystals, the polishing process adopts mechanical polishing for rough polishing, wherein the diamond suspension particle size is 3-9 μm and the pressure is 10-20 N / cm 2 , the speed is 100-200rpm; chemical polishing is used for fine polishing, wherein the polishing liquid is alkaline colloidal silica (pH 9-11) and aluminum oxide nanoparticles (0.05-0.2μm), the ratio of polishing liquid to water is 1:5, and the pressure is 5-10N / cm 2 , the speed is 30~60rpm, and the time is 2~4h; finally, ion beam polishing is used for final polishing to make the surface roughness The energy of the argon ion beam is 1 to 3 keV, the incident angle is 5° to 15°, and the scanning speed is 0.1 to 0.5 mm / s.

[0019] On the other hand, the present invention also provides a method for preparing a strontium lanthanum tantalate twinned crystal, wherein the strontium lanthanum tantalate twinned crystal seed is pulled and grown to obtain the strontium lanthanum tantalate twinned crystal, which specifically comprises the following steps:

[0020] S1. Surface treatment is performed on the lanthanum strontium aluminate twinned seed crystal to obtain the treated lanthanum strontium aluminate twinned seed crystal. The outer dimension error of the treated seed crystal is required to be ±0.01mm and the surface roughness is

[0021] S2. Place the strontium lanthanum aluminate twinned seed crystal processed in step S1 into a pulling device and perform twinned growth in an oxygen atmosphere to obtain a strontium lanthanum aluminate twinned crystal. The grown strontium lanthanum aluminate twinned crystal is annealed in an oxygen atmosphere, specifically by naturally cooling the grown strontium lanthanum aluminate twinned crystal to 1000-1100°C in an oxygen atmosphere, then maintaining the temperature at 1000-1100°C for 2-10 hours, and then slowly cooling the crystal at a rate of 20-50°C / h. This is to adjust the oxygen content, eliminate oxygen vacancy defects, and eliminate grain boundary residual stress.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention first uses a traditional sintering method to prepare a first strontium lanthanum aluminate tantalate twin crystal mother material, from which a rectangular crystal blank is cut as a seed crystal, and then uses a pulling method to prepare a large-sized strontium lanthanum aluminate tantalate twin crystal, from which a rectangular crystal blank is cut as a seed crystal for subsequent growth of crystals; the twin crystals grown in this way have naturally closed grain boundaries, no voids, no defects, no external dust particle contamination, and a dense and uniform structure, which solves the problem of twin crystal grain boundary contamination.

[0024] 2. When the twin crystal seed crystal is pulled and grown, the present invention adjusts the oxygen pressure of the furnace through the air inlet and exhaust port on the pulling device to isolate external dust and avoid the loss of oxygen during the crystal growth process; a thermal insulation layer is added around the crucible to ensure a uniform temperature field. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0026] Figure 1Schematic diagram of the first twinned seed crystal structure of the present invention: (a) crystal plane index; (b) actual image of the grain boundary.

[0027] Figure 2 Schematic diagram of the cross-sectional structure of the pulling device of the present invention;

[0028] Main legend:

[0029] 1-furnace body, 2-furnace cover, 3-crucible, 4-induction heating coil, 5-insulation layer, 6-exhaust port, 7-exhaust valve, 8-air inlet, 9-air inlet valve, 10-lifting rod, 11-twinned seed crystal. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Unless otherwise defined, all technical terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

[0031] Example 1

[0032] A method for preparing strontium lanthanum tantalate twinned seed crystals comprises the following steps:

[0033] (1) A sintering method is used to prepare a first strontium lanthanum tantalate twinned crystal matrix, the specific steps being:

[0034] A1. Select lanthanum strontium aluminate single crystals with a purity of ≥99.9999%, good single crystallinity, no twins, no inclusions, no bubbles, no scattering, and all crystal faces immersed in the melt are (001) crystal faces with an angle of 6° between the crystal faces;

[0035] A2. Orient, cut, rough polish, chemical polish, and ion beam polish according to the required twin crystal boundary angle and size. The surface roughness of the twin crystal interface is required to be

[0036] A3. Use optical adhesive to completely bond the two crystal blocks together. The crystal interface after optical adhesive bonding must be completely bonded without any bubbles.

[0037] A4. The bonded twin ingot was placed in a high-temperature sintering furnace in an argon and 4% oxygen atmosphere for pre-sintering and high-temperature sintering. The pre-sintering temperature was 750°C for 3 hours, and the high-temperature sintering temperature was 1600°C for 4 hours. The sintering pressure was 150 MPa. The ingot was then annealed at a cooling rate of 500°C / hour to obtain the first lanthanum strontium aluminate twinned crystal matrix.

[0038] (2) Using diamond wire, the first twin crystal of strontium aluminum tantalate (grain boundary physical picture see Figure 1 (b)) A contamination-free, uniform grain boundary with a grain boundary line width in the nanometer scale is cut out. Figure 1 As shown in (a), as the first twinned seed crystal, the twinned seed crystal has a size of 5 mm × 5 mm × 10 mm, and the three crystal plane indices are (100) (plane C), (010) (plane B), and (001) (plane A, immersed in the melt) crystal planes;

[0039] (2) The first twin crystal seed crystal is subjected to rough polishing, chemical polishing, and ion beam polishing to obtain the processed first twin crystal seed crystal. The outer dimension error of the processed first twin crystal seed crystal is required to be ±0.01mm, and the surface roughness is

[0040] (3) placing the first twinned seed crystal into a pulling device for pulling growth;

[0041] Lifting device such as Figure 2 As shown, it includes a furnace body 1, a furnace cover 2, and a growth system. The furnace cover 2 is removably and sealed and installed above the furnace body 1. The growth system is located inside the furnace body 1 and includes a crucible 3 and a lifting rod 10. An induction heating coil 4 is installed on the outer wall of the crucible 3. A bottom support 12 is provided at the bottom of the crucible 3. The bottom support 12 can be adjusted up and down to adjust the height of the crucible 3 to cooperate with the crystal lifting operation of the lifting rod 10 and adapt to various types of crucibles. An insulation layer 5 is provided around the crucible 3 to ensure a uniform temperature field. The lifting rod 10 is suspended above the crucible 3 and can move up and down and rotate. The furnace cover 2 is provided with an air inlet 8 and an air inlet valve 9. The bottom of the furnace body 1 is provided with an exhaust port 6 and an exhaust valve 7.

[0042] The pulling growth process specifically includes: placing lanthanum strontium aluminate tantalate raw material at the bottom of a crucible, fixing the twinned seed crystal on a pulling rod using a molybdenum mechanical fixture, sealing the pulling device, heating through an induction coil, and when the raw material is completely melted and the melt flow line is clear and stable, introducing oxygen through an air inlet, using the (001) crystal plane of the seed crystal as the immersion surface in the melt, slowly lowering the seed crystal, and after the seed crystal contacts the melt surface, adjusting the furnace temperature to 1500-1700°C, the oxygen pressure to 1-5 atm, the pulling speed to 1-3 mm / h, and the rotation speed to 15-25 rpm to pull and grow the twinned crystal;

[0043] (4) Using a diamond wire, a cubic crystal blank of 5 mm × 5 mm × 10 mm with uniform grain boundaries and a grain boundary line width of no more than 1 nm is cut from the second strontium lanthanum aluminate twin crystal mother material obtained in step (3) to obtain a strontium lanthanum aluminate twin crystal seed crystal for preparing a strontium lanthanum aluminate twin crystal.

[0044] The above rough polishing, chemical polishing and ion beam polishing are specifically as follows:

[0045] The polishing process adopts mechanical polishing method for rough polishing, in which the diamond suspension particle size is 3-9μm and the pressure is 10-20N / cm 2 , the speed is 100-200rpm; chemical polishing is used for fine polishing, wherein the polishing liquid is alkaline colloidal silica (pH 9-11) and aluminum oxide nanoparticles (0.05-0.2μm), the ratio of polishing liquid to water is 1:5, and the pressure is 5-10N / cm 2 , the speed is 30~60rpm, and the time is 2~4h; finally, ion beam polishing is used for final polishing to make the surface roughness The energy of the argon ion beam is 1 to 3 keV, the incident angle is 5° to 15°, and the scanning speed is 0.1 to 0.5 mm / s.

[0046] Example 2

[0047] A method for preparing strontium lanthanum tantalate twinned crystals comprises the following steps:

[0048] S1. The strontium lanthanum aluminate twin seed crystals obtained in Example 1 are ground, polished, chemically polished, and cleaned to obtain the treated strontium lanthanum aluminate twin seed crystals. The outer dimension error of the treated seed crystals is required to be ±0.01 mm, and the surface roughness is

[0049] S2. Place the lanthanum strontium aluminate tantalate raw material at the bottom of the crucible, fix the twin crystal seed crystal on the pulling rod, seal the pulling device, and heat it through the induction coil. When the raw material is completely melted and the melt flow line is clear and stable, introduce oxygen through the air inlet, use the (001) crystal plane of the seed crystal as the immersion surface in the melt, slowly lower the seed crystal, and after the seed crystal contacts the melt surface, adjust the furnace temperature to 1500-1700℃, the oxygen pressure to 1-5atm, the pulling speed to 1-3mm / h and the rotation speed to 15-25rpm to pull and grow the twin crystal. To ensure uniformity, defect-freeness, and crystal quality of the pulled twin crystal boundaries, it is necessary to maintain thermodynamic and kinetic balance at the grain boundaries. That is, in the early stages of grain boundary formation, the heating power should be reduced to reduce the disturbance of the melt convection on the interface; the pulling speed should be appropriately reduced to reduce stress accumulation at the grain boundaries; and the rotation speed should be appropriately increased to optimize melt convection and promote uniform mixing of the melt on both sides of the grain boundary, thereby ensuring grain boundary uniformity, reducing defects, and improving crystal quality.

[0050] S3. Annealing the grown strontium lanthanum aluminate tantalate twin crystals in an oxygen atmosphere. Specifically, the grown strontium lanthanum aluminate tantalate twin crystals are naturally cooled to 1000-1100°C in the oxygen atmosphere, then maintained at 1000-1100°C for 2-10 hours, and then slowly cooled at a rate of 20-50°C / h. This eliminates grain boundary residual stress and repairs oxygen vacancies.

[0051] The above rough polishing, chemical polishing and ion beam polishing are specifically as follows:

[0052] The polishing process adopts mechanical polishing method for rough polishing, in which the diamond suspension particle size is 3-9μm and the pressure is 10-20N / cm 2 , the speed is 100-200rpm; chemical polishing is used for fine polishing, wherein the polishing liquid is alkaline colloidal silica (pH 9-11) and aluminum oxide nanoparticles (0.05-0.2μm), the ratio of polishing liquid to water is 1:5, and the pressure is 5-10N / cm 2 , the speed is 30~60rpm, and the time is 2~4h; finally, ion beam polishing is used for final polishing to make the surface roughness The energy of the argon ion beam is 1 to 3 keV, the incident angle is 5° to 15°, and the scanning speed is 0.1 to 0.5 mm / s.

[0053] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A twinned strontium lanthanum tantalate aluminate seed crystal, characterized in that: The strontium lanthanum tantalate aluminate twinned seed crystal is prepared by the following method: first, a first strontium lanthanum tantalate aluminate twinned crystal mother material is prepared by a sintering method, and a rectangular crystal blank with intact grain boundaries is cut out from the first twinned crystal mother material as a first twinned seed crystal; a large-sized second strontium lanthanum tantalate aluminate twinned crystal mother material is prepared by a pulling method, and then a rectangular crystal blank is cut out from the second strontium lanthanum tantalate aluminate twinned crystal mother material to obtain a strontium lanthanum tantalate twinned seed crystal.

2. A method for preparing a twinned seed crystal of strontium lanthanum tantalate aluminate according to claim 1, characterized in that: The following steps are involved: (1) preparing a first twinned crystal base material of strontium lanthanum aluminate tantalate by a sintering method, and cutting it by diamond wire cutting at a cutting speed of 0.1 to 1 mm / min to obtain a rectangular solid crystal blank with uniform grain boundaries and grain boundary line widths in the nanometer scale as a first twinned seed crystal; (2) The first twin crystal seed crystal is subjected to surface treatment, which includes rough polishing, chemical polishing, and ion beam polishing to obtain the treated first twin crystal seed crystal. The outer dimension error of the treated first twin crystal seed crystal is required to be ±0.01 mm, and the surface roughness is (3) placing the first twinned seed crystal into a pulling device, and performing twinned growth by pulling in an oxygen atmosphere to obtain a second strontium lanthanum tantalate aluminum twinned crystal mother material; (4) Cutting the second strontium lanthanum aluminate twin crystal mother material obtained in step (3) into a rectangular solid with uniform grain boundaries and grain boundary line widths in the nanometer scale to obtain a strontium lanthanum aluminate twin crystal seed crystal for preparing a strontium lanthanum aluminate twin crystal.

3. The method for preparing strontium lanthanum tantalate aluminate twinned seed crystals according to claim 2, characterized in that: The first twinned seed crystal and the strontium lanthanum aluminate tantalate twinned seed crystal are rectangular parallelepipeds with a size of 3-5 mm×3-5 mm×5-10 mm.

4. The method for preparing strontium lanthanum tantalate aluminate twinned seed crystals according to claim 2, wherein: The twin grain boundary angle is 6°, 12°, 18°, 24°, 30° or 36°.

5. The method for preparing strontium lanthanum tantalate aluminate twinned seed crystals according to claim 2, wherein: The pulling device includes a furnace body, a furnace cover, and a growth system. The furnace cover is detachably and sealedly installed above the furnace body. The growth system is located inside the furnace body and includes a crucible. A base is provided at the bottom of the crucible, an induction heating coil is provided on the outer wall of the crucible, and an insulation layer is provided around the crucible. A pulling rod is suspended above the crucible and can move up and down and rotate. An air inlet and an air inlet valve are provided on the furnace cover, and an exhaust port and an exhaust valve are provided at the bottom of the furnace body.

6. The method for preparing strontium lanthanum tantalate aluminate twinned seed crystals according to claim 5, characterized in that: The twin crystal pulling and growing process includes: placing lanthanum strontium aluminate tantalate raw material into the bottom of a crucible, sealing a pulling device, heating through an induction coil, completely melting the raw material, and when the melt flow lines are clear and stable, slowly lowering the seed crystal from the side containing the grain boundary of the seed crystal. After the seed crystal contacts the melt surface, the furnace temperature, oxygen pressure, pulling speed and rotation speed are adjusted to pull and grow the twin crystal.

7. The method for preparing strontium lanthanum tantalate aluminate twinned seed crystals according to claim 6, characterized in that: The furnace temperature is 1500-1700° C., the oxygen pressure is 1-5 atm, the pulling speed is 1-3 mm / h, and the rotation speed is 15-25 rpm.

8. The method for preparing strontium lanthanum tantalate aluminate twinned seed crystals according to claim 2, wherein: The polishing process adopts mechanical polishing method for rough polishing, wherein the diamond suspension particle size is 3-9 μm and the pressure is 10-20 N / cm 2 , the speed is 100-200rpm; chemical polishing is used for fine polishing, wherein the polishing liquid is alkaline colloidal silica (pH 9-11) and aluminum oxide nanoparticles (0.05-0.2μm), the ratio of polishing liquid to water is 1:5, and the pressure is 5-10N / cm 2 , the speed is 30~60rpm, and the time is 2~4 hours; finally, ion beam polishing is used for final polishing to make the surface roughness The energy of the argon ion beam is 1 to 3 keV, the incident angle is 5° to 15°, and the scanning speed is 0.1 to 0.5 mm / s.

9. A method for preparing twinned crystals of strontium lanthanum tantalate aluminate, characterized in that: The strontium lanthanum aluminate tantalate twinned crystal seed crystal according to claim 1 is subjected to Czochralski growth to obtain the strontium lanthanum aluminate twinned crystal, which specifically comprises the following steps: S1. Surface treatment is performed on the lanthanum strontium aluminate twinned seed crystal to obtain the treated lanthanum strontium aluminate twinned seed crystal. The outer dimension error of the treated seed crystal is required to be ±0.01mm and the surface roughness is S2. Place the strontium lanthanum aluminate twinned seed crystal processed in step S1 into a pulling device, and perform twinned crystal pulling growth in an oxygen atmosphere to obtain a strontium lanthanum aluminate twinned crystal.

10. The method for preparing strontium lanthanum tantalate aluminate twinned crystals according to claim 9, characterized in that: In step S2, the grown strontium lanthanum aluminate tantalate twin crystal is naturally cooled to 1000-1100° C. in an oxygen atmosphere, then kept at 1000-1100° C. for 2-10 hours, and then cooled at a cooling rate of 20-50° C. / h.

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