A method for growing an LSGM single crystal by a pulling method

Abstract

The application discloses a method for growing LSGM single crystal by a pulling method and belongs to the technical field of single crystal growth. The method provided by the application comprises the following steps: ingredients of La2O3, SrCO3, Ga2O3 and MgO are prepared according to a mass ratio of (60.5-62.0):(2.5-3.5):(36.2-38.2):(0.6-1.2), mixed, pressed, and then solid-phase sintered to obtain LSGM embryo material; then the growth of LSGM single crystal is carried out by a pulling method; and the atmosphere used in the growth process is a mixed atmosphere of oxygen, carbon dioxide and nitrogen, and the volume ratio of oxygen, carbon dioxide and nitrogen is (0.5-2):(65-75):(25-35). The application effectively overcomes the volatilization and decomposition problems of Ga2O3 in the process of growing LSGM single crystal by a pulling method, and can grow high-quality LSGM single crystal meeting the requirements of a substrate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single crystal growth, in particular to a method for growing LSGM single crystal by Czochralski method. BACKGROUND

[0002] The information disclosed in the background section of the present application is only intended to increase an understanding of the general context of the present application and does not necessarily constitute an acknowledgement or any form of suggestion that this information forms part of the prior art already known to those skilled in the art.

[0003] LSGM (La 0.95 Sr 0.05 Ga 0.95 Mg 0.05 O 3-δ ) is a kind of fast ionic conductor material with perovskite structure, which has good ion transport performance and chemical stability, and shows excellent pure oxygen ion conductivity in medium temperature range, and is widely used in solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) and other fields. At present, the research report on the preparation of LSGM single crystal is very limited.

[0004] The patent with publication number CN107268073A reports a method for preparing LSGM fast ionic conductor single crystal by Czochralski growth. The patent successfully grows a 2-inch diameter LSGM single crystal using the Czochralski method in an argon atmosphere. Ghislain et al. (Journal of The Electrochemical Society, 2016, 163: F1189-F97) successfully grew a 20 mm diameter, about 35 mm length LSGM single crystal by the Czochralski method in a nitrogen atmosphere at a pulling rate of 2.5 mm / h and a rotation speed of 20 rpm.

[0005] However, the inventors found that when nitrogen or argon is used as the growth atmosphere, the stability of Ga2O3 is poor, and the volatilization and decomposition of Ga2O3 at high temperature is serious, which leads to the decrease of Ga2O3 content in the raw material, and the alloying of Ga produced by decomposition with iridium crucible and mold, resulting in the loss of precious metals. Therefore, how to provide a growth method for inhibiting Ga decomposition and obtaining high-quality LSGM single crystal is a problem to be solved. SUMMARY

[0006] Therefore, the present application provides a method for growing LSGM single crystal by Czochralski method, which can quickly and stably grow high-quality and large-size LSGM single crystal, and effectively slow down the loss of iridium.

[0007] The present application provides a method for growing LSGM single crystal by Czochralski method, comprising the following steps:

[0008] La2O3, SrCO3, Ga2O3 and MgO are proportioned according to a mass ratio of (60.5-62.0):(2.5-3.5):(36.2-38.2):(0.6-1.2), mixed, pressed, and then solid-phase sintered to obtain LSGM blanks;

[0009] Then, a LSGM single crystal is grown by using a pulling method; and the atmosphere used in the growing process is a mixed atmosphere of oxygen, carbon dioxide and nitrogen, and the volume ratio of oxygen, carbon dioxide and nitrogen is (0.5-2):(65-75):(25-35).

[0010] Compared with the prior art, the present application has the following beneficial effects:

[0011] The present application grows a LSGM single crystal by using a pulling method under a mixed atmosphere of oxygen, carbon dioxide and nitrogen, and Ga2O3 raw material is slightly excessive to compensate for the loss caused by volatilization at high temperature, thus effectively overcoming the volatilization and decomposition of Ga2O3 in the process of growing a LSGM single crystal by using a pulling method, effectively slowing down the loss of iridium crucibles, and growing a high-quality LSGM single crystal meeting the requirements of substrates. BRIEF DESCRIPTION OF DRAWINGS

[0012] The drawings constituting a part of the specification of the present application are used to provide further understanding of the present application, the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute improper limitations on the present application. Obviously, for those skilled in the art, other drawings can be obtained from these drawings without creative labor.

[0013] Figure 1 is a sample photo of a LSGM single crystal of Example 1 of the present application;

[0014] Figure 2 is an upper X-ray Laue diffraction pattern of an equal-diameter part of a LSGM single crystal of Example 1 of the present application;

[0015] Figure 3 is a lower X-ray Laue diffraction pattern of an equal-diameter part of a LSGM single crystal of Example 1 of the present application;

[0016] Figure 4 is an X-ray diffraction pattern of a LSGM single crystal of Example 1 of the present application and a LSGM blank prepared by high-temperature sintering in step (1);

[0017] Figure 5 is an X-ray Laue diffraction pattern of an equal-diameter part of a LSGM single crystal of Comparative Example 1 of the present application;

[0018] Figure 6is the LSGM single crystal isometric part X-ray Laue diffraction pattern of the present application comparative example 2;

[0019] Figure 7 is the LSGM single crystal isometric part X-ray Laue diffraction pattern of the present application comparative example 3;

[0020] Figure 8 is the LSGM single crystal conductivity change graph at different temperatures of the present application example 1 and comparative examples 1-3. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, 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 application belongs.

[0022] The present application provides a method for growing LSGM single crystal by Czochralski method, comprising the following steps:

[0023] La2O3, SrCO3, Ga2O3 and MgO are prepared according to the mass ratio (60.5-62.0) : (2.5-3.5) : (36.2-38.2) : (0.6-1.2), mixed, pressed, and then solid-phase sintered to obtain LSGM embryo material;

[0024] Then the LSGM single crystal is grown by Czochralski method; the atmosphere used in the growth process is a mixed atmosphere of oxygen, carbon dioxide and nitrogen, and the volume ratio of oxygen, carbon dioxide and nitrogen is (0.5-2) : (65-75) : (25-35).

[0025] The present application finds that when LSGM single crystal is grown in pure nitrogen or pure argon environment, the stability of Ga2O3 is poor, and the volatilization and decomposition phenomenon is serious at high temperature, and the quality of the obtained LSGM single crystal is poor. The present application obtains the optimal atmosphere condition for growing LSGM single crystal by Czochralski method through a large number of experiments, and the present application can effectively overcome the volatilization and decomposition problem of Ga2O3 in the process of growing LSGM single crystal by Czochralski method under the condition of a mixed atmosphere of oxygen, carbon dioxide and nitrogen in a specific ratio and slightly excessive Ga2O3 raw material, and effectively slows down the loss of iridium crucible, and can grow high-quality LSGM single crystal meeting the substrate requirements.

[0026] The purity of La2O3, SrCO3, Ga2O3 and MgO used in the present application is above 99.99%. The present application does not make special restrictions on the source of the raw materials with the above-mentioned purity, and commercially available raw materials with lower purity can be purified to obtain raw materials with high purity. The present application does not make special restrictions on the specific purification steps, and those skilled in the art can use common means in the art for purification.

[0027] In the present application, the rotation speed of the mixing process is 30-50 rpm, and the mixing time is 40-100 h. In one or more embodiments of the present application, the mixing process is carried out in a mixer, and the longer mixing time ensures that the four reactants are well mixed, which is beneficial to the occurrence of subsequent reactions and the preparation of high-quality LSGM single crystals with high uniformity. The present application does not make special restrictions on the pressing process, for example, a hydraulic press can be used to press into blocks or isostatic pressing to press into columnar rods, and those skilled in the art can choose according to actual needs.

[0028] In the present application, the process of solid phase sintering is specifically as follows: the pressed solid is sintered in an air atmosphere at 1100-1300℃ for 60-100 h.

[0029] In the present application, the specific process of growing LSGM single crystal by the Czochralski method is as follows: the LSGM embryo material is placed in a crystal growth furnace, a mixed atmosphere of oxygen, carbon dioxide and nitrogen is filled after vacuumizing, the LSGM embryo material is heated and melted, then necking, shoulder releasing, isodiametric growth and tailing are carried out, the crystal is pulled out after the crystal grows to the required size, and then the temperature is lowered to room temperature to obtain the LSGM single crystal.

[0030] In the present application, the filling pressure of the mixed atmosphere of oxygen, carbon dioxide and nitrogen is 1-1.1 bar, and more preferably one atmosphere.

[0031] In the present application, the LSGM embryo material is placed in an iridium crucible in the crystal growth furnace; the iridium crucible has good high-temperature resistance and thermal deformation resistance; but Ga produced by decomposition may form an alloy with the iridium crucible and the mold during the growth of the LSGM single crystal, resulting in its loss. The present application effectively overcomes the volatilization and decomposition of Ga2O3 through atmosphere control, thereby effectively slowing down the loss of the iridium crucible,

[0032] In the present application, the LSGM embryo material is placed in a crystal growth furnace, and the vacuum degree is (0.5-2) x 10 -4 Pa.

[0033] The present application does not make special restrictions on the heating method for heating and melting the LSGM embryo material, and the present application preferably uses a medium-frequency induction heating method.

[0034] The present application does not make special restrictions on the specific necking, shoulder, equal-diameter growth and tailing stages, and the commonly used pulling method process in the art can be used. The necking process in the present application is preferably that the LSGM seed crystal is introduced and necked under the condition that the temperature is 1-3°C higher than the melting point of the LSGM melt; and the LSGM seed crystal is selected from a <110> direction seed crystal. After the <110> direction seed crystal is selected, the present application further includes the steps of cutting, ultrasonic cleaning and drying.

[0035] In the present application, the pulling speed of the necking, shoulder, equal-diameter growth and tailing stages is 0.8-1.2 mm / h, and the rotation speed is 5-20 rpm.

[0036] In the present application, after the crystal is grown to the required size, the temperature is increased by 15-30°C, kept constant for 20-40 min, and then the crystal is pulled out. In the present application, the cooling rate of the process of reducing to room temperature is 10-30°C / h.

[0037] The technical solutions of the present application are further described below in combination with specific examples. The present application does not make special restrictions on the sources of the reagents used in the following examples, and commercially available goods well known to those skilled in the art can be used. The purity of La2O3, SrCO3, Ga2O3 and MgO in the following examples is all 99.99%.

[0038] Example 1

[0039] The present embodiment provides a method for growing LSGM single crystal by the pulling method. Specifically, the method includes the following steps:

[0040] (1) Selection and treatment of raw materials

[0041] La2O3, SrCO3, Ga2O3 and MgO are weighed according to the mass ratio of 61.1:2.9:36.5:0.8, then the above four kinds of raw materials are mixed for 72 hours, and then pressed into a sheet. Then, the temperature is increased to 1200°C at a heating rate of 50°C / h, and sintered for 72h to obtain LSGM blank, which is ready for use.

[0042] (2) Selection of seed crystal

[0043] The LSGM seed crystal is selected from a <110> direction seed crystal, which is cut, ultrasonically cleaned, dried and ready for use.

[0044] (3) Growing LSGM single crystal by the melt pulling method

[0045] The LSGM blank of step (1) is loaded into an iridium crucible in the crystal growth furnace, and the size of the crucible is Φ60mm×60mm; the crystal growth furnace is vacuumed to 1×10 -4Pa, oxygen, carbon dioxide and nitrogen are filled to one atmosphere, and the volume fractions of oxygen, carbon dioxide and nitrogen are 1%, 70% and 29% respectively; the LSGM billet is heated and melted by using a medium frequency induction heating mode.

[0046] The LSGM seed crystal is introduced at 2℃ higher than the melting point of the melt, and the necking is performed, and when the diameter of the seed crystal is thinned to 2mm, the shoulder is performed, and after the equal-diameter growth, the finishing stage is entered; the pulling speed in the necking, shoulder, equal-diameter growth and finishing stages is 1mm / hour, and the rotation speed is 10rpm.

[0047] After the crystal is grown to the required size, the temperature is increased by 20℃, and the crystal is pulled out of the melt after constant temperature for 30 minutes.

[0048] After the crystal is pulled out, the temperature is decreased to room temperature at a rate of 15℃ / h, and the LSGM single crystal is obtained.

[0049] The LSGM single crystal prepared in the embodiment is shown in Figure 1 .

[0050] The growth direction and single crystal nature of the LSGM single crystal prepared in the embodiment are tested by X-ray Laue diffraction method, and the results are shown in Figure 2 and Figure 3 . Figure 2 and Figure 3 The diffraction point patterns are measured for the near (110) surface, and the test points are in the upper and lower parts of the equal-diameter part of the crystal. From Figure 2 and Figure 3 , it can be seen that the diffraction point distribution is clear and obvious, and the crystal quality is good; the diffraction pattern is consistent with the theory, and the patterns of the upper and lower parts are the same, which indicates that the directional growth of the crystal is realized.

[0051] The LSGM single crystal prepared and the LSGM billet prepared by high-temperature sintering in step (1) are respectively subjected to X-ray diffraction test. The results are shown in Figure 4 , the black line is the standard PDF card of LaGaO3 crystal, the No. 2 line is the test result of the raw material after high-temperature sintering, and the No. 1 line is the test result of the prepared LSGM single crystal. From Figure 4 , it can be seen that the LSGM billet after high-temperature sintering and the prepared LSGM single crystal do not have impurity peaks.

[0052] Example 2

[0053] The embodiment provides a method for growing LSGM single crystal by a pulling method. Specifically, the method comprises the following steps:

[0054] (1) Selection and treatment of raw materials

[0055] La2O3, SrCO3, Ga2O3 and MgO are proportioned according to the mass ratio of 61.9:2.8:37.1:0.9, and then the above four raw materials are mixed for 72 hours and pressed into a sheet. After that, the temperature is raised to 1200℃ high temperature sintering at a temperature rising rate of 50℃ / h for 72h, to obtain LSGM blank, ready for use.

[0056] (2) Selection of seed crystal

[0057] The LSGM seed crystal is selected in the direction of <110>, and after cutting, ultrasonic cleaning and drying, it is ready for use.

[0058] (3) Growth of LSGM single crystal by melt pulling method

[0059] The LSGM blank of step (1) is loaded into the iridium crucible in the crystal growth furnace, and the crucible size is Φ60mm×60mm; the crystal growth furnace is vacuumed to 1×10 -4 Pa, and oxygen, carbon dioxide and nitrogen are filled to one atmosphere, wherein the volume fractions of oxygen, carbon dioxide and nitrogen are 2%, 72% and 26% respectively; the LSGM blank is heated and melted by using the intermediate frequency induction heating method.

[0060] The LSGM seed crystal is inserted at 2℃ higher than the melting point of the melt and is necked, and when the diameter of the seed crystal is thinned to 2mm, the shoulder is released, and after the constant diameter growth, the tailing stage is entered; the pulling speed of the necking, shoulder releasing, constant diameter growth and tailing stage: 2mm / hour, rotation speed: 10 revolutions / minute.

[0061] After the crystal is grown to the required size, the temperature is raised by 20℃, and the temperature is kept constant for 30 minutes, and the crystal is pulled out of the melt.

[0062] After the crystal is pulled out, the temperature is lowered to room temperature at a rate of 15℃ / h, and the LSGM single crystal is obtained.

[0063] Example 3

[0064] The present embodiment provides a method for growing LSGM single crystal by pulling method. Specifically, it comprises the following steps:

[0065] (1) Selection and treatment of raw materials

[0066] La2O3, SrCO3, Ga2O3 and MgO are proportioned according to the mass ratio of 61.9:2.8:37.1:0.9, and then the above four raw materials are mixed for 72 hours and pressed into a sheet. After that, the temperature is raised to 1200℃ high temperature sintering at a temperature rising rate of 50℃ / h for 72h, to obtain LSGM blank, ready for use.

[0067] (2) Selection of seed crystal

[0068] The LSGM seed crystal is selected in <110> direction, cut, ultrasonically cleaned, and dried for standby.

[0069] (3) Growth of LSGM single crystal by melt pulling method

[0070] The LSGM embryo material of step (1) is loaded into an iridium crucible in a crystal growth furnace, and the crucible size is Φ60mm*60mm; the crystal growth furnace is vacuumed to 1*10 -4 Pa, and oxygen, carbon dioxide and nitrogen are filled to one atmosphere pressure, wherein the volume fractions of oxygen, carbon dioxide and nitrogen are 1%, 70% and 29% respectively; the LSGM embryo material is heated and melted by a medium frequency induction heating method.

[0071] The LSGM seed crystal is inserted at 2℃ higher than the melting point of the melt and necked down, and the shoulder is performed when the seed crystal diameter is thinned to 2mm, and after the constant diameter growth, the tailing stage is entered; the pulling speed of the necking, shoulder, constant diameter growth and tailing stage is 1mm / hour, and the rotation speed is 13rpm.

[0072] After the crystal is grown to the required size, the temperature is increased by 20℃, and the temperature is kept constant for 30 minutes, and the crystal is pulled out from the melt.

[0073] After the crystal is pulled out, the temperature is decreased to room temperature at a rate of 15℃ / h, and the LSGM single crystal is obtained.

[0074] Example 4

[0075] The embodiment provides a method for growing LSGM single crystal by a pulling method. Specifically, the method comprises the following steps:

[0076] (1) Selection and treatment of raw materials

[0077] La2O3, SrCO3, Ga2O3 and MgO are weighed according to the mass ratio of 61.0:2.9:36.7:1.0, then the four kinds of raw materials are fully mixed for 72 hours, and then pressed into a sheet. Then, the temperature is increased to 1200℃ at a rate of 50℃ / h, and sintered for 72h to obtain LSGM embryo material for standby.

[0078] (2) Selection of seed crystal

[0079] The LSGM seed crystal is selected in <110> direction, cut, ultrasonically cleaned, and dried for standby.

[0080] (3) Growth of LSGM single crystal by melt pulling method

[0081] The LSGM embryo material of step (1) is loaded into an iridium crucible in a crystal growth furnace, and the crucible size is Φ60mm*60mm; the crystal growth furnace is vacuumed to 1*10 -4Pa, oxygen, carbon dioxide and nitrogen are filled to one atmosphere pressure, wherein the volume fractions of oxygen, carbon dioxide and nitrogen are 0.8%, 68% and 31.2% respectively; the LSGM embryo is heated and melted by using a medium frequency induction heating mode.

[0082] The LSGM seed crystal is introduced at 2℃ higher than the melting point of the melt and is necked down, the shoulder is formed when the diameter of the seed crystal is necked down to 2mm, after the equal diameter growth, the finishing stage is entered; the pulling speed in the necking down, shoulder forming, equal diameter growth and finishing stages is 2mm / hour, and the rotation speed is 10rpm.

[0083] After the crystal is grown to the required size, the temperature is increased by 20℃, and the crystal is pulled out of the melt after constant temperature for 30 minutes.

[0084] After the crystal is pulled out, the temperature is decreased to room temperature at a rate of 15℃ / h, and the LSGM single crystal is obtained.

[0085] Example 5

[0086] The present embodiment provides a method for growing LSGM single crystal by the Czochralski method. Specifically, the method comprises the following steps:

[0087] (1) Selection and treatment of raw materials

[0088] La2O3, SrCO3, Ga2O3 and MgO are weighed according to the mass ratio of 61.0:3.0:36.8:0.9, then the above four kinds of raw materials are mixed for 72 hours, and are pressed into a sheet. Then the temperature is increased to 1200℃ at a rate of 50℃ / h, and sintered for 72h to obtain LSGM embryo, which is ready for use.

[0089] (2) Selection of seed crystal

[0090] The LSGM seed crystal is selected in the direction of <110>, and is cut, ultrasonically cleaned and dried for standby use.

[0091] (3) Growing LSGM single crystal by the melt pulling method

[0092] The LSGM embryo of step (1) is loaded into the iridium crucible in the crystal growth furnace, and the size of the crucible is Φ60mm×60mm; the crystal growth furnace is vacuumed to 1×10 -4 Pa, oxygen, carbon dioxide and nitrogen are filled to one atmosphere pressure, wherein the volume fractions of oxygen, carbon dioxide and nitrogen are 0.8%, 68% and 31.2% respectively; the LSGM embryo is heated and melted by using a medium frequency induction heating mode.

[0093] The LSGM seed crystal was introduced into the melt at 2℃ higher than the melting point of the melt and necked down, and when the diameter of the seed crystal was reduced to 3mm, the shoulder was formed, and after the equal-diameter growth, the end was formed. The pulling speed in the necking, shoulder forming, equal-diameter growth and end forming stages was 2mm / hour, and the rotation speed was 10rpm.

[0094] After the crystal was grown to the required size, the temperature was increased by 20℃, and kept constant for 30 minutes, and the crystal was pulled out from the melt.

[0095] After the crystal was pulled out, the temperature was decreased to room temperature at a rate of 15℃ / h, and the LSGM single crystal was obtained.

[0096] Comparative Example 1

[0097] The difference between the present comparative example and Example 1 is that in the present comparative example, the volume fractions of oxygen, carbon dioxide and nitrogen are 0.5%, 80% and 19.5%, respectively.

[0098] The X-ray Laue diffraction pattern of the LSGM single crystal obtained in the present comparative example is shown in Figure 5 It can be seen that the diffraction point distribution is not as clear as Figure 2 and Figure 3 , indicating that the crystal quality obtained in the present example is not as good as that of Example 1.

[0099] Comparative Example 2

[0100] The difference between the present comparative example and Example 1 is that in the present comparative example, the atmosphere in the crystal growth furnace is oxygen and carbon dioxide, and the volume fractions of oxygen and carbon dioxide are 1% and 99%, respectively.

[0101] The X-ray Laue diffraction pattern of the LSGM single crystal obtained in the present comparative example is shown in Figure 6 It can be seen that the diffraction point distribution is not as clear as Figure 2 and Figure 3 , indicating that the crystal quality obtained in the present example is not as good as that of Example 1.

[0102] Comparative Example 3

[0103] The difference between the present comparative example and Example 1 is that in the present comparative example, the atmosphere in the crystal growth furnace is pure nitrogen.

[0104] The X-ray Laue diffraction pattern of the LSGM single crystal obtained in the present comparative example is shown in Figure 7 It can be seen that the diffraction point distribution is not as clear as Figure 2 and Figure 3 , indicating that the crystal quality obtained in the present example is not as good as that of Example 1.

[0105] Test Example

[0106] The LSGM single crystals prepared in Example 1 and Comparative Examples 1 to 3 were subjected to conductivity measurement at different temperatures, and the results are shown in Table 1. Figure 8 As can be seen, the LSGM single crystal prepared in Example 1 has the most excellent conductivity.

[0107] The above descriptions are merely preferred embodiments of the present application, but not intended to limit the present application. Various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall within the scope of the present application.

Claims

1. A method for growing LSGM single crystals using the Czochralski method, characterized in that, Includes the following steps: La2O3, SrCO3, Ga2O3 and MgO were mixed in a mass ratio of (60.5~62.0):(2.5~3.5):(36.2~38.2):(0.6~1.2), pressed, and then solid-state sintered to obtain LSGM blank. Then, the Czochralski method was used to grow LSGM single crystals; the atmosphere used in the growth process was a mixed atmosphere of oxygen, carbon dioxide and nitrogen, and the volume ratio of oxygen, carbon dioxide and nitrogen was (0.5~2):(65~75):(25~35).

2. The method as described in claim 1, characterized in that, The mixing process involves a rotation speed of 30–50 rpm and a mixing time of 40–100 h.

3. The method as described in claim 1, characterized in that, The solid-state sintering process specifically involves placing the pressed solid in an air atmosphere at 1100–1300°C for sintering for 60–100 hours.

4. The method as described in claim 1, characterized in that, The specific process of growing LSGM single crystals using the Czochralski method is as follows: The LSGM preform is placed in a crystal growth furnace, and after vacuuming, a mixed atmosphere of oxygen, carbon dioxide and nitrogen is introduced. The LSGM preform is heated and melted, and then necking, shouldering, constant diameter growth and tailing are performed. After the crystal grows to the required size, the crystal is removed and cooled to room temperature to obtain the LSGM single crystal.

5. The method as described in claim 4, characterized in that, The filling pressure of the mixed atmosphere of oxygen, carbon dioxide and nitrogen is 1 to 1.1 bar.

6. The method as described in claim 4, characterized in that, The LSGM preform was placed in an iridium crucible within the crystal growth furnace; a vacuum was then evacuated to a vacuum level of (0.5–2) × 10⁻⁶. -4 Pa.

7. The method as described in claim 4, characterized in that, The lifting speed during the necking, shoulder expansion, equal diameter growth, and tailing stages is (0.8~1.2) mm / h, and the rotation speed is 5~20 rpm.

8. The method as described in claim 4, characterized in that, After the crystal has grown to the required size, heat it to 15–30°C and hold it at that temperature for 20–40 minutes, then remove the crystal.

9. The method as described in claim 4, characterized in that, The cooling rate during the process of reducing the temperature to room temperature is 10–30 °C / h.

10. The method as described in claim 4, characterized in that, The necking process involves inserting an LSGM seed crystal and necking it at a temperature 1–3°C above the melting point of the LSGM melt; the LSGM seed crystal is selected from... <110> Seed crystals in a specific direction.

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