Synthesis device and synthesis process of Tb-based ternary fluoride raw material

Abstract

The invention discloses a synthesis device and a synthesis process of a Tb-based ternary fluoride raw material. The synthesis device comprises a vacuum cavity, and a stirring part is arranged in the vacuum cavity; the heat preservation cavity is formed in the vacuum cavity, an opening is formed in the upper end of the heat preservation cavity, and a heating element is arranged in the heat preservation cavity; the high-temperature-resistant container is arranged in the heat preservation cavity; wherein the heating element is used for heating the high-temperature-resistant container; the stirring part is used for stirring reaction materials in the high-temperature-resistant container. The invention also discloses a synthesis process, and the oxygen-free and high-purity Tb-based ternary fluoride raw material can be prepared through the synthesis device and the synthesis process provided by the invention.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and in particular relates to a synthesis device and a synthesis process of a Tb-based ternary fluoride raw material for growing a magneto-optical functional crystal. Background Art

[0002] In recent years, with the development of high-power laser technology, magneto-optical isolators have been widely studied and applied. Magneto-optical isolators are a kind of laser unidirectional transmission component. Its basic structure includes polarizer, analyzer, annular permanent magnet along the axial direction and magneto-optical crystal material. Magneto-optical isolators can effectively isolate reflected light in high-power laser systems, thereby achieving the purpose of protecting the front-end system. Magneto-optical crystal material is the core component of magneto-optical isolators. Commonly used oxide magneto-optical crystal materials (such as Tb3Ga5O 12 、Tb3Sc2Al3O 12 ), generally have a high absorption coefficient (~0.2% cm -1 @1064nm), large thermo-optical coefficient (1.79×10 -5 / K), which limits its application in high-power laser systems.

[0003] Around 2017, SYNOPTICS of the United States launched LiTbF4 and KTb3F 10 Ternary fluoride magneto-optical crystals show low absorption (<0.02% cm -1 @1064nm), small thermo-optical coefficient (~1×10 -6 / K), large Verdet constant (>35rad / T·m), and other excellent properties. Based on this type of crystal element, a high-performance magneto-optical isolator was prepared, verifying its application in high-power laser systems. However, during the growth of ternary fluoride magneto-optical crystals, fluoride oxide inclusions, precipitation phases, bubbles, etc. are easily generated. High-quality LiTbF4, KTb3F 10 Crystal growth is difficult. This is mainly because the binary fluorides TbF3, LiF, and KF, the raw materials for growth, are very easy to deliquesce, forming crystal water and forming fluoride oxides during the growth stage.

[0004] Therefore, controlling LiTbF4, KTb3F 10 The oxygen content in the melt is the key to producing high-quality crystals. In the preparation of other similar ternary fluorides (LiYF4), the ingredients are usually prepared according to a specific ratio of YF3 and LiF, and the materials are chemically processed. The floating fluoride oxides are salvaged to reduce the oxygen content and increase the purity of the melt before the LiYF4 crystals are grown. However, in the preparation of LiTbF4 and KTb3F 10 During the crystal preparation process, TbF 31-x O xThe melting point is low and it will not float in the form of solid particles on LiTbF4 and KTb3F 10 The existing process can only provide binary fluoride raw materials such as TbF3, LiF, and KF, which cannot meet the requirements of high-quality LiTbF4, KTb3F 10 Crystal. SYNOPTICS of the United States has developed high-quality LiTbF4, KTb3F 10 Crystals, however, the details of high-purity raw material synthesis and crystal growth process technology are always kept secret. Therefore, it is urgent to synthesize high-purity, oxygen-free raw materials for high-quality LiTbF4, KTb3F 10 Crystal growth. Summary of the invention

[0005] In view of this, the primary purpose of the present invention is to provide a synthesis device and a synthesis process for a Tb-based ternary fluoride raw material, so as to prepare an oxygen-free, high-purity Tb-based ternary fluoride raw material.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The first aspect of the present invention provides a synthesis device for a Tb-based ternary fluoride raw material, comprising:

[0008] A vacuum cavity, wherein a stirring portion is provided in the vacuum cavity;

[0009] A heat preservation chamber is arranged inside the vacuum chamber, the upper end of the heat preservation chamber is open, and a heating element is arranged inside the heat preservation chamber;

[0010] and a high temperature resistant container, which is placed in the heat preservation chamber;

[0011] Wherein, the heating element is used to heat the high temperature resistant container; and the stirring part is used to stir the reaction material in the high temperature resistant container.

[0012] The second aspect of the present invention provides a synthesis process of a Tb-based ternary fluoride raw material based on the synthesis device described above, comprising the following steps:

[0013] S1. Mix the raw materials evenly in a high temperature resistant container and seal it under the condition of isolating water and oxygen;

[0014] S2, evacuate the vacuum chamber, and then introduce inert gas to 1.0×10 5 ~1.3×10 5 Pa;

[0015] S3, placing the sealed raw materials in a heat preservation chamber, and continuously introducing inactive gas into the vacuum chamber during the process;

[0016] S4, unsealing the raw material, evacuating the vacuum chamber again, and heating to melt the raw material;

[0017] S5, introducing CF4 and inactive gas into the vacuum chamber;

[0018] S6, maintaining the temperature in step S4, and fully stirring the melted raw materials;

[0019] S7, stop introducing CF4, and continue to introduce inactive gas;

[0020] S8. Cool the synthesis device to room temperature, stop introducing inactive gas, and take out the reaction raw materials.

[0021] Beneficial effects of the present invention:

[0022] The synthesis device and synthesis process of the present invention can prepare a high-purity, oxygen-free Tb-based ternary fluoride raw material, and the Tb-based ternary fluoride raw material can be used to prepare high-quality Tb-based ternary fluoride crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of a synthesis device in a preferred embodiment of the present invention.

[0024] Figure 2 This is the XRD characterization result of the LiTbF4 raw material in Example 1 of the present invention.

[0025] Figure 3 KTb3F in Example 2 of the present invention 10 XRD characterization results of raw materials.

[0026] In the figure: 10-vacuum chamber, 11-platform, 12-flange cover, 13-vacuum obtaining part, 14-first gas supply pipeline, 15-second gas supply pipeline; 20-stirring part, 21-liftable and rotatable part; 30-insulating chamber, 31-heating element; 40-high temperature resistant container, 41-melt. DETAILED DESCRIPTION

[0027] Embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In addition, unless otherwise specified, methods that do not specifically record conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial sources.

[0029] In a preferred embodiment of the present invention, a synthesis device for a Tb-based ternary fluoride raw material is first provided, and its structure is as follows: Figure 1 As shown in .

[0030] The synthesis device includes a vacuum chamber 10, which is used to provide a place for raw material synthesis and has the characteristics of high temperature resistance and corrosion resistance. A heat preservation chamber 30 is provided in the vacuum chamber 10, and a heating element 31 is provided in the heat preservation chamber 30. At the same time, a high temperature resistant container 40 for holding raw materials is placed in the heat preservation chamber 30. High-purity, oxygen-free Tb-based ternary fluoride raw materials can be prepared by the synthesis device.

[0031] Specifically, the inner wall of the vacuum chamber 10 is provided with a corrosion-resistant coating. The setting of these corrosion-resistant coatings is to prevent the raw materials from corroding the vacuum chamber 10 during the synthesis process, thereby affecting the service life of the device and even the purity of the corresponding subsequent synthesis environment. The materials of these corrosion-resistant coatings can be selected according to actual needs. In this embodiment, the corrosion-resistant coating is a polytetrafluoroethylene coating. A stirring part 20 is provided on the vacuum chamber 10, and the stirring end of the stirring part 20 extends into the interior of the vacuum chamber 10 to stir the melt 41 in the high-temperature resistant container 40. In this embodiment, the end of the stirring part 20 away from the stirring end is connected to a lifting and rotating part 21, which is fixed on the vacuum chamber 10. Through the drive of the lifting and rotating part 21, the stirring part 20 can realize the lifting and rotating operations. In addition, the stirring part 20 should be selected from a material that is inert to the raw materials and products of the reactants and the reaction gas. In this embodiment, the material of the stirring part 20 is platinum. Furthermore, the vacuum chamber 10 is also provided with an opening, which is sealed by a flange cover 12. On the one hand, the sealing requirement of the vacuum chamber 10 can be achieved, and on the other hand, the high temperature resistant container 40 can be conveniently taken out and placed by opening the flange cover 12. Furthermore, the vacuum chamber 10 is also provided with a plurality of openings connected to external pipelines, which can introduce corresponding gases or conditions according to experimental needs; in this embodiment, one of the openings is connected with a vacuum obtaining part 13, which refers to any device that can provide a vacuum environment for the vacuum chamber 10. In this embodiment, the vacuum obtaining part 13 is a molecular pump vacuum unit. In addition, there are two openings respectively connected with a first gas supply line 14 and a second gas supply line 15, the first gas supply line 14 is used to introduce CF4 gas into the vacuum chamber 10, and the second gas supply line 15 is used to introduce an inert gas into the vacuum chamber 10, wherein the inert gas refers to a gas that is inert to the reaction raw materials or other reaction gases, for example, it can be a rare gas, preferably helium or argon. In the present invention, the role of CF4 is to remove water and oxygen impurities contained in the raw materials through fluorination reaction. In the present invention, CF4 is used as a substitute for HF gas and has the advantage of high safety. At the same time, since CF4 is also corrosive to a certain extent, a certain inert gas is used to dilute the CF4 gas, and the reaction product is discharged through the air flow. Preferably, the volume ratio of CF4 to the inert gas is 1: (2 to 3).

[0032] It is understandable that corresponding valves are provided in these pipelines to facilitate the introduction and stopping of operating gas.

[0033] The heat preservation chamber 30 is a chamber with an opening at the top, and the heating element 31 is disposed in the heat preservation chamber 30 for heating the high temperature resistant container 40 in the heat preservation chamber 30. In the present embodiment, a platform 11 is disposed in the vacuum chamber 10, and the platform 11 penetrates the heat preservation chamber 30, so that the high temperature resistant container 40 is placed in the heat preservation chamber 30. The heat preservation chamber 30 and the heating element 31 are both made of graphite. In the present embodiment, the heat preservation chamber 30 is graphite felt, and the heating element 31 is hot pressed graphite.

[0034] Furthermore, the high temperature resistant container 40 contains a melt 41 of raw materials. In this embodiment, the high temperature resistant container 40 is a platinum crucible.

[0035] In another preferred embodiment of the present invention, a synthesis process of a Tb-based ternary fluoride raw material based on the synthesis device described above is provided, comprising the following steps:

[0036] S1. Mix the raw materials evenly in a high temperature resistant container and seal it under the condition of isolating water and oxygen;

[0037] S2, evacuate the vacuum chamber, and then introduce inert gas to 1.0×10 5 ~1.3×10 5 Pa;

[0038] S3, placing the sealed raw materials in a heat preservation chamber, and continuously introducing inactive gas into the vacuum chamber during the process;

[0039] S4, unsealing the raw material, evacuating the vacuum chamber again, and heating to melt the raw material;

[0040] S5, introducing CF4 and inactive gas into the vacuum chamber;

[0041] S6, maintaining the temperature in step S4, and fully stirring the melted raw materials;

[0042] S7, stop introducing CF4, and continue to introduce inactive gas;

[0043] S8. Cool the synthesis device to room temperature, stop introducing inactive gas, and take out the reaction raw materials.

[0044] In the present invention, the Tb-based ternary fluoride is a fluoride composed of three elements, one of which is Tb, and is particularly a ternary fluoride that can be used as a magneto-optical crystal, such as LiTbF4 or KTb3F 10 , but it is not limited to this.

[0045] In the present invention, the water-oxygen isolation condition refers to a water-oxygen content of less than 0.5 ppm, which can generally be achieved by a conventional glove box in the art, but is not limited thereto. The specific ratio of the raw materials can be prepared according to the actual molar ratio, so there is no special limitation.

[0046] In the present invention, the vacuum degree of the vacuum chamber can be adjusted according to actual needs, preferably not less than 5×10 -4 Pa shall prevail.

[0047] In the present invention, the temperature of melting the raw materials varies according to the raw materials, and can be within the melting point range of the raw materials. For example, for LiTbF4 raw materials, the temperature is set at 860-880°C; for KTb3F 10 Raw materials, the temperature is set at 1060 ~ 1080 ℃.

[0048] In the present invention, the role of introducing CF4 gas is to safely remove water and oxygen impurities contained in the raw materials through fluorination reaction. At the same time, since CF4 also has a certain corrosiveness, the volume of CF4: inactive gas = 1: (2 to 3) is used to dilute the CF4 gas, and the reaction product is discharged through the air flow.

[0049] In the present invention, the melt is continuously stirred to ensure full reaction of the reaction raw materials, and during the stirring process, the gas is introduced to discharge the reaction products as much as possible by using the gas flow to improve the purity of the raw materials.

[0050] In the present invention, the cooling rate is not particularly limited and can be selected according to actual conditions, and preferably can be 50-60° C. / h.

[0051] The technical solution of the present invention is more clearly described below through specific embodiments.

[0052] Example 1

[0053] This embodiment provides a synthesis process of LiTbF4 raw material, and the specific steps are as follows:

[0054] (1) In a glove box with a water and oxygen content of less than 0.5 ppm, 5 kg of raw materials were weighed according to a molar ratio of LiF:TbF3 = 57:43, mixed evenly in a high-temperature resistant container 40 with an inner diameter of 120 mm, a depth of 150 mm, and a thickness of 1 mm, and the loaded high-temperature resistant container 40 was sealed with a sealing bag and taken out of the glove box.

[0055] (2) Evacuate the vacuum chamber 10 to 5×10 -4 Pa, and then high-purity Ar (5N) gas was filled into the vacuum chamber 10 at 200 sccm to a pressure of 1.1×10 5 Pa, open the flange cover 12 and continue to introduce high-purity Ar (5N) gas.

[0056] (3) After the loaded high temperature resistant container 40 is placed into the heat preservation chamber 30 of the vacuum chamber 10 , the sealing bag is cut open and taken out, and the flange cover 12 is put on to seal the vacuum chamber 10 .

[0057] (4) The vacuum chamber 10 is evacuated again to a temperature of 5×10 -4 After Pa, the temperature in the heat preservation chamber 30 is raised to 860-880°C to melt the raw materials.

[0058] (5) Open the CF4 valve in the first gas supply line 14 and the Ar valve in the second gas supply line 15 respectively, and introduce CF4 and Ar at a rate of 30 sccm and 70 sccm.

[0059] (6) Slowly extend the stirring portion 20 into the melt 41 in the high temperature resistant container 40, and stir the melt 41 forwardly and reversely at a rate of 10 rad / min.

[0060] (7) Maintain the temperature at 860-880°C and stir thoroughly for 12 hours.

[0061] (8) Close the CF4 gas valve and continue to introduce Ar gas.

[0062] (9) The temperature of the heat preservation chamber 30 is cooled to room temperature at a rate of 60°C / h, the Ar gas valve is closed, the flange cover 12 is opened, and the high temperature resistant container 40 containing the synthesized LiTbF4 raw material is taken out.

[0063] Figure 2 The XRD spectrum of the LiTbF4 raw material prepared in this embodiment is shown in FIG. 1 . It can be seen that the polycrystalline diffraction peak is relatively sharp, and the peak position can correspond one by one to the diffraction peak in the standard card, indicating that there are no other phase impurities in the raw material, which meets the definition of high purity.

[0064] Comparative Example 1

[0065] This comparative example provides another synthesis process of LiTbF4 raw material, and the specific steps are as follows:

[0066] (1) In a glove box, weigh 5 kg of raw materials according to the molar ratio of LiF:TbF3=57:43, mix them evenly in a platinum boat with a length of 120 mm, a width of 80 mm, a depth of 50 mm, and a thickness of 1 mm; put the platinum boat into a corundum tube, seal the two ends of the corundum tube with flanges, and take it out of the glove box.

[0067] (2) Place the corundum tube into a horizontal double-temperature zone furnace, and connect one end of the corundum tube to the CF4 and Ar gas pipelines with a flange.

[0068] (3) Raise the temperature in the furnace to 860-880°C to melt the raw materials.

[0069] (4) Open the CF4 valve and Ar valve respectively, and introduce CF4 and Ar at rates of 30 Sccm and 70 Sccm.

[0070] (5) Maintain the temperature at 1060-1080°C for 12 hours.

[0071] (6) Close the CF4 gas valve and continue to introduce Ar gas.

[0072] (7) Cool the furnace temperature to room temperature at a rate of 60°C / h, close the Ar gas valve, open the flange cover, and take out the platinum boat containing the synthetic raw materials.

[0073] Table 1 shows the EDS energy spectrum analysis results of the LiTbF4 raw materials in Example 1 and Comparative Example 1.

[0074] Table 1 EDS spectrum analysis results of LiTbF4 raw materials

[0075] Check out elements Tb(at%) F(at%) O(at%) C (at%) Tb:F Example 1 24.8 75.2 0 0 1:3.03 Comparative Example 1 22.5 61.1 9.6 6.8 1:2.72

[0076] EDS energy spectrum scanning can semi-quantitatively characterize the content of each element in the sample. The test results in Table 1 show that no oxygen impurities appear in the ternary fluoride LiTbF4 raw material synthesized by the synthesis process in Example 1. It should be noted that since the Li element is relatively light and cannot be detected by EDS energy spectrum, it is not listed in Table 1.

[0077] Example 2

[0078] This embodiment provides a KTb3F 10 The synthetic process of raw materials, the specific steps are as follows:

[0079] (1) In a glove box, 5 kg of raw materials were weighed according to the molar ratio of KF:TbF3=57:43, mixed evenly in a high temperature resistant container 40 with an inner diameter of 120 mm, a depth of 150 mm, and a thickness of 1 mm, and the loaded high temperature resistant container 40 was sealed with a sealing bag and taken out of the glove box.

[0080] (2) At the same time, the vacuum chamber 10 is evacuated to 5×10 -4 Pa, and then high-purity Ar (5N) gas was filled into the vacuum chamber 10 at 200 sccm to a pressure of 1.1×10 5 Pa, open the flange cover 12 and continue to introduce high-purity Ar (5N) gas.

[0081] (3) After the loaded high temperature resistant container 40 is placed into the heat preservation chamber 30 of the vacuum chamber 10 , the sealed bag is cut open and taken out, and the flange cover 12 is covered.

[0082] (4) The vacuum chamber 10 is evacuated again to a temperature of 5×10 -4After Pa, the temperature in the heat preservation chamber 30 is raised to 1060-1080°C to melt the raw materials.

[0083] (5) Open the CF4 valve in the first gas supply line 14 and the Ar valve in the second gas supply line 15 respectively, and introduce CF4 and Ar at a rate of 30 sccm and 70 sccm.

[0084] (6) Slowly extend the stirring portion 20 into the melt 41, stir the melt 41 forwardly and reversely at a rate of 10 rad / min, and keep the melt 41 constant at 1060-1080° C. and stir it fully for 12 h.

[0085] (7) Close the CF4 gas valve and continue to introduce Ar gas.

[0086] (8) Cool the temperature of the heat preservation chamber 30 to room temperature at a rate of 60°C / h, close the Ar gas valve, open the flange cover 12, and take out the KTb3F 10 A high temperature resistant container 40 for raw materials.

[0087] Figure 3 The KTb3F prepared in this example is shown in 10 From the XRD spectrum of the raw material, it can be seen that the polycrystalline diffraction peak is relatively sharp, and the peak position can correspond one by one with the diffraction peak in the standard card, indicating that there are no other phase impurities in the raw material, which meets the definition of high purity.

[0088] Comparative Example 2

[0089] This comparative example provides another KTb3F 10 The synthetic process of raw materials, the specific steps are as follows:

[0090] (1) In the glove box, weigh 5 kg of raw materials according to the molar ratio of KF:TbF3=57:43, and mix them evenly in a platinum boat with a length of 120 mm, a width of 80 mm, a depth of 50 mm, and a thickness of 1 mm. Put the platinum boat into the corundum tube, seal the two ends of the corundum tube with flanges, and take it out of the glove box.

[0091] (2) Place the corundum tube into a horizontal double-temperature zone furnace, and connect one end of the corundum tube to the CF4 and Ar gas pipelines with a flange.

[0092] (3) Raise the temperature in the furnace to 1060-1080°C to melt the raw materials.

[0093] (4) Open the CF4 valve and Ar valve respectively, and introduce CF4 and Ar at rates of 30 Sccm and 70 Sccm.

[0094] (5) Maintain the temperature at 1060-1080°C for 12 hours.

[0095] (6) Close the CF4 gas valve and continue to introduce Ar gas.

[0096] (7) Cool the furnace temperature to room temperature at a rate of 60°C / h, close the Ar gas valve, open the flange cover, and take out the platinum boat containing the synthetic raw materials.

[0097] Table 2 shows the KTb3F in Example 2 and Comparative Example 2. 10 EDS energy spectrum analysis results of raw materials.

[0098] Table 2KTb3F 10 EDS spectrum analysis results of raw materials

[0099]

[0100]

[0101] It can be concluded from the test results in Table 2 that the ternary fluoride KTb3F synthesized by the synthesis process in Example 2 10 No oxygen impurities are present in the raw materials.

[0102] By comparing Examples 1-2 and Comparative Examples 1-2, it can be concluded that the ratio of each element in the Tb-based ternary fluoride raw material synthesized using the process of the present invention is closer to the stoichiometric ratio, does not contain impurities such as O and C, and has a higher purity.

[0103] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0104] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A synthesis device for Tb-based ternary fluoride raw materials, characterized in that: include: A vacuum cavity, wherein a stirring portion is provided in the vacuum cavity; A heat preservation chamber is arranged inside the vacuum chamber, the upper end of the heat preservation chamber is open, and a heating element is arranged inside the heat preservation chamber; and a high temperature resistant container, which is placed in the heat preservation chamber; Wherein, the heating element is used to heat the high temperature resistant container; and the stirring part is used to stir the reaction material in the high temperature resistant container.

2. The synthesis device according to claim 1, characterized in that The inner wall of the vacuum cavity is provided with a corrosion-resistant coating, and the vacuum cavity is provided with a sealable opening; Preferably, the corrosion-resistant coating is a polytetrafluoroethylene coating, and the opening is sealed with a flange cover.

3. The synthesis device according to claim 1, characterized in that The vacuum cavity is provided with a vacuum obtaining part, and the vacuum obtaining part is used to provide a vacuum environment inside the vacuum cavity.

4. The synthesis device according to claim 1, characterized in that The vacuum chamber is provided with a plurality of valves, and the valves are used to provide a reaction atmosphere into the vacuum chamber; Preferably, the reaction atmosphere is CF4 gas and / or inert gas; Preferably, the inert gas is a rare gas; Preferably, the inert gas is argon or helium.

5. The synthesis device according to claim 1, characterized in that The heat preservation chamber and the heating element are both made of graphite; Preferably, the insulation chamber is graphite felt, and the heating element is hot-pressed graphite.

6. The synthesis device according to claim 1, characterized in that The high temperature resistant container is a platinum crucible; and / or the stirring part is a liftable stirring rod, and the material of the stirring part is platinum.

7. A synthesis process of a Tb-based ternary fluoride raw material, the synthesis process is carried out based on the synthesis device according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Place the raw materials in a high temperature resistant container, mix them evenly and seal them under the condition of isolating water and oxygen; S2, evacuate the vacuum chamber, and then introduce inert gas to 1.0×10 5 ~1.3×10 5 Pa; S3, placing the sealed raw materials in a heat preservation chamber, and continuously introducing inactive gas into the vacuum chamber during the process; S4, unsealing the raw material, evacuating the vacuum chamber again, and heating to melt the raw material; S5, introducing CF4 and inactive gas into the vacuum chamber; S6, maintaining the temperature in step S4, and fully stirring the melted raw materials; S7, stop introducing CF4, and continue to introduce inactive gas; S8. Cool the synthesis device to room temperature, stop introducing inactive gas, and take out the reaction raw materials.

8. The synthesis process according to claim 7, characterized in that In steps S2 and S4, the vacuum degree of the vacuum chamber is not less than 5×10 -4 Pa.

9. The synthesis process according to claim 7, characterized in that: In step S4, the temperature of the molten raw material is 860-1080°C.

10. The synthesis process according to claim 7, characterized in that: In step S5, the flow rate of the CF4 gas is 20-30 sccm, and the flow rate of the inactive gas is 60-70 sccm.

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