Integrated production device and method of lithium niobate single domain crystal

Abstract

The application relates to a lithium niobate single-domain crystal integrated production device and a production method, which comprises the following steps: a furnace body is provided with an upper and lower separated crystal annealing chamber and a crystal growth chamber, the crystal annealing chamber and the crystal growth chamber are communicated through a communication hole, a first heating part is fixedly arranged in the crystal growth chamber, and a second heating part is fixedly arranged in the crystal annealing chamber; a crucible is arranged in the crystal growth chamber and opposite to the communication hole; a polarization assembly is arranged for polarizing the crystal, and the polarization assembly is provided with a polarization barrel for containing the crystal; a translation mechanism is arranged for driving the polarization barrel to horizontally move so as to open or close the communication hole; a pulling assembly is arranged for connecting a seed crystal; and a pulling mechanism is arranged for driving the pulling assembly to ascend and descend and for separating the pulling assembly from the seed crystal. The growing-annealing-polarizing operation is integrated in one device, the production process steps are optimized, the total production cycle is greatly shortened, and the single crystal production energy consumption is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of lithium niobate crystal production technology, specifically to an integrated production apparatus and method for lithium niobate single-domain crystals. Background Technology

[0002] Lithium niobate crystal (LiNbO3) is a crucial multifunctional ferroelectric material. Due to its excellent piezoelectric, acousto-optic and nonlinear optical properties, it is widely used in fields such as surface acoustic wave filters and quantum light sources.

[0003] Currently, the Czochralski method is mainly used for the growth of lithium niobate crystals in industrial production. However, the Czochralski growth process itself is extremely time-consuming. After growth, the lithium niobate crystal requires a separate high-temperature thermal annealing process to release internal thermal stress and obtain a uniform material suitable for device applications. Furthermore, lithium niobate is a ferroelectric material. Within its crystal lattice, the centers of positive and negative charges do not coincide, forming a tiny electric dipole moment, known as spontaneous polarization. In untreated crystals, these spontaneous polarization directions are randomly distributed, forming many small regions with different orientations, called domains. By applying a strong electric field (higher than the coercive field), the spontaneous polarization directions of almost all domains within the crystal can be aligned to the same side; this process is called polarization or single-domain treatment. After polarization, the crystal changes from a multi-domain state to a single-domain state.

[0004] Current lithium niobate crystal production processes require independent completion of each step in multiple devices, resulting in a lengthy cycle. The primary crystals grown using the Czochralski method exhibit significant thermal stress, making them susceptible to cracking and damage due to temperature variations. Under current methods, the grown crystals must be slowly cooled within the growth furnace over a certain period to release some stress before being removed. They are then transferred to a separate muffle furnace for secondary heating and prolonged annealing at temperatures above the Curie temperature (approximately 1142°C).

[0005] For example, patent CN 111206282A discloses a method for producing 8-inch lithium niobate crystals, which includes the following steps: (1) Preparation of polycrystalline raw materials: Lithium carbonate and niobium oxide raw materials are mixed, sintered, and then pressed and crushed to obtain polycrystalline raw materials; (2) Crystal growth: The polycrystalline raw material is placed in a platinum crucible located in a multi-layer temperature field, and the crystal is grown by the Czochralski method. After crystal pulling, necking, shoulder formation, shoulder reduction, constant diameter growth, and pulling, a multi-domain crystal is obtained. (3) Annealing and polarization of the crystal: The multi-domain crystal is embedded in the polycrystalline raw material and annealed and polarized to obtain the 8-inch lithium niobate crystal. The annealing process in step (3) is as follows: heating time from 30℃ to 200℃ is 170~190min, heating time from 200℃ to 1100℃ is 1070~1090min, heating time from 1100℃ to 1230℃±5℃ is 390~410min; holding time is 550~650min; cooling to 1170℃±10℃ after 170~190min, holding for 230~250min, cooling to 950℃ after 1650~1750min, cooling to 600℃ after 410~430min.

[0006] As can be seen from step 3, the annealing process involves first raising the temperature from room temperature (30℃) to 1230℃, then holding the temperature at 1230℃ for annealing, and finally cooling down, which is a very long process.

[0007] The crystals obtained through this patent's lengthy growth cycle must first be cooled to room temperature (30°C), then transferred to an annealing apparatus for a second heating process before undergoing annealing and polarization. This separate processing mode of "growth-cooling-transfer-heating-thermal annealing-polarization" results in a total preparation cycle of 3-4 weeks. This lengthy cycle not only extends product delivery time and limits production throughput, but also leads to repeated energy consumption and a significant increase in production costs. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing an integrated production apparatus and method for lithium niobate single-domain crystals. It integrates the growth-annealing-polarization processes, significantly shortening the overall production cycle and effectively reducing energy consumption in single-crystal production by optimizing the production process steps. This invention holds extremely urgent strategic significance and clear industrial necessity for enhancing my country's industrial competitiveness in lithium niobate crystal preparation, ensuring the independent and controllable supply of core materials, and promoting the innovative development of downstream optoelectronic industries.

[0009] The present invention is achieved through the following technical solution: an integrated production device for lithium niobate single-domain crystals, comprising: a furnace body, wherein the furnace body has a crystal annealing chamber and a crystal growth chamber separated by upper and lower sections, the crystal annealing chamber and the crystal growth chamber are connected by a connecting hole, a plurality of first heating elements are fixedly disposed in the crystal growth chamber, and a plurality of second heating elements are fixedly disposed in the crystal annealing chamber. A crucible, which is located in a crystal growth chamber and is positioned opposite to a connecting hole, with a number of first heating elements distributed around the crucible; A polarization assembly is used to polarize a crystal. The polarization assembly has a polarization barrel for holding the crystal. The polarization barrel is located in the crystal annealing chamber. Several second heating elements are distributed around the polarization barrel. The outer diameter of the polarization barrel is larger than the diameter of the connecting hole. Translation mechanism is used to drive the polarization barrel to move horizontally, so that the polarization barrel can open or close the connecting hole; A lifting assembly is used to connect the seed crystal. The lifting assembly includes a seed crystal rod and a seed crystal chuck. The seed crystal rod is vertically inserted through the top of the furnace body, and the lower end of the seed crystal rod is located inside the furnace body and is fixedly connected to the seed crystal chuck. The lifting mechanism is used to drive the lifting assembly to move up and down so that the seed crystal chuck can reciprocate between the crystal annealing chamber and the crystal growth chamber through the connecting hole. It is also used to drive the lifting assembly to separate from the seed crystal.

[0010] This design integrates the crystal growth chamber and the crystal annealing chamber into a single furnace body. The two chambers can be heated separately by a first heating element and a second heating element. In operation, crystal growth is first performed in the crystal growth chamber. Driven by a lifting mechanism, the grown crystal is moved to the crystal annealing chamber for annealing and polarization. During annealing and polarization, the crystal is collected in a polarization container of the polarization assembly, facilitating both annealing and direct polarization afterward. This integrated growth-annealing-polarization process significantly improves production efficiency and saves costs. Since the crystal does not pass through external contaminants during movement, there is no need for cooling or secondary heating before annealing, greatly shortening the annealing process cycle and the overall production cycle. Furthermore, the device uses a translation mechanism to move the polarization container of the polarization assembly, facilitating crystal collection during use. Furthermore, during annealing, the connecting hole is closed by blocking the polarization barrel, which completely separates the crystal growth chamber and the crystal annealing chamber, thereby ensuring the stability of the temperature field in the two chambers.

[0011] As an optimization, the polarization assembly includes an upper electrode plate, a lower electrode plate, a feeding tube, and a polarization tank. The lower electrode plate is located at the bottom of the polarization tank, and the upper electrode plate is located at the top of the polarization tank. A polarization zone for polarizing the crystal is formed between the upper and lower electrode plates. The upper and lower electrode plates are respectively connected to the positive and negative terminals of an external power supply via platinum wires. The feeding tube is used to add polarized polycrystalline material into the polarization tank. This optimized scheme uses an external power supply to pass positive and negative currents to the upper and lower electrode plates, creating a strong electric field between them to polarize the multi-domain crystal. During polarization, to ensure a stable temperature and field in the chamber, the polarized polycrystalline material is added to the polarization tank through the feeding tube, eliminating the need to open the furnace door and improving ease of use.

[0012] As an optimization, the upper electrode plate is slidably mounted on the side wall of the polarization tank, with the sliding direction of the upper electrode plate being the same as the translation direction of the polarization tank. A first push-pull rod is slidably mounted on the side wall of the crystal annealing chamber, and the first push-pull rod is fixedly connected to the upper electrode plate and drives the upper electrode plate to slide. In this optimized solution, the upper electrode plate adopts a sliding pull-out setting. By pulling the upper electrode plate with the first push-pull rod, the top opening of the polarization tank is made available, making it easier to put the crystal into the polarization tank and improving the convenience of use.

[0013] As an optimization, the translation mechanism includes a second push-pull rod, which slides through the side wall of the crystal annealing chamber. The second push-pull rod is fixedly connected to the polarization barrel and drives the polarization barrel to translate. This optimized solution uses the second push-pull rod to pull the polarization barrel to slide, resulting in a simple structure and convenient use.

[0014] As an optimization, the seed crystal chuck has a U-shaped structure, and the seed crystal has a T-shaped structure. In this optimized design, the T-shaped seed crystal can be vertically clamped into the groove of the U-shaped seed crystal chuck, resulting in higher stability after connection. Furthermore, it facilitates separation during annealing, preventing heat conduction along the seed crystal chuck during crystal annealing and thus reducing annealing quality.

[0015] As an optimization, the lifting mechanism includes a vertical beam fixed to the top of the furnace body. A lifting seat is slidably mounted on one side of the vertical beam, and a supporting crossbeam is fixed to one side of the lifting seat. A fixed seat is slidably mounted on the bottom of the supporting crossbeam. A linear drive mechanism is provided on the supporting crossbeam to drive the fixed seat to slide horizontally. A first motor is mounted on the fixed seat, with the output shaft of the first motor facing downwards. An elongated sliding hole is opened at the top of the furnace body, and the upper end of the seed crystal rod passes through the elongated sliding hole and is fixedly connected to the output shaft of the first motor. In this optimized scheme, the lifting mechanism raises and lowers the lifting assembly by sliding the lifting seat up and down. The lifting assembly rotates through the output of the first motor and, in conjunction with the linear drive mechanism, drives the first motor to slide horizontally, causing the lifting assembly to shift horizontally, thereby achieving the separation of the seed crystal chuck from the seed crystal.

[0016] A method for producing the above-mentioned lithium niobate single-domain crystal using the aforementioned production apparatus is characterized by comprising the following steps: S1. Prepare lithium niobate polycrystalline material: Place the lithium niobate polycrystalline material, which is made by mixing and sintering lithium carbonate and niobium oxide raw materials, in a crucible and suspend the seed crystal on the seed crystal chuck of the pulling component. S2. Crystal growth: The crystal growth chamber is heated by the first heating element, which melts the lithium niobate polycrystalline material into liquid polycrystalline material; the lifting mechanism drives the lifting component to descend, so that the seed crystal moves to the crystal growth chamber, and the crystal is grown by the lifting method. After seeding, necking, shouldering, constant diameter growth, tailing, and pulling, lithium niobate multidomain crystal is obtained. S3. Annealing heating: After the lithium niobate multidomain crystal is made, it is not cooled down, but is kept warm in the crystal growth chamber. At the same time, it is heated by the second heating element to raise the temperature of the crystal annealing chamber and maintain it at the annealing temperature. S4. Crystal Annealing: The pulling mechanism drives the pulling assembly to rise, moving the uncooled lithium niobate multidomain crystal to the crystal annealing chamber; the translation mechanism drives the polarization barrel to move horizontally, closing the connecting hole; the pulling mechanism drives the pulling assembly to fall, placing the lithium niobate multidomain crystal in the polarization barrel; the pulling mechanism drives the seed crystal chuck of the pulling assembly to separate from the lithium niobate multidomain crystal; the lithium niobate multidomain crystal is held at the annealing temperature to complete the hot annealing operation and release the crystal thermal stress. S5. Crystal Polarization: After annealing, the lithium niobate multidomain crystal is added to the polarization tank through the feeding tube, so that the lithium niobate multidomain crystal is embedded in the polarization polycrystalline material; an external power supply is used to pass current through the upper and lower electrode plates to apply polarization current to the lithium niobate multidomain crystal; the current is maintained for a certain period of time to perform polarization operation on the lithium niobate multidomain crystal; then the annealing temperature is cooled to below the crystal Curie temperature and the current is removed to obtain a lithium niobate single-domain crystal; S6. Cool the lithium niobate single-domain crystal to room temperature in a stepwise manner.

[0017] This method integrates growth, annealing, and polarization into a single device. Since no external transfer is required during operation, the grown crystal does not need to be cooled or heated again before annealing, thus greatly shortening the annealing process cycle and significantly reducing the overall production cycle.

[0018] As an optimization, in step S4, the annealing temperature of the crystal annealing chamber is 1200℃, and the holding time is 9.5~10h.

[0019] As an optimization, in step S5, the polarization current density of the lithium niobate multidomain crystal is 2~3 mA / cm². 2 The external power supply is gradually applied to the polarization current at a rate of 1~2mA / min; after the polarization current is applied, it is held for 30-60min; the annealing temperature is reduced to 1100℃ at a rate of 15℃ / h, and then the current is removed at 1~2mA / min.

[0020] As an optimization, in step S6, the stepped cooling procedure is as follows: A. Cooling rate of 20℃ / h from 1100℃ to 800℃; B. Cooling down at 30℃ / h from 800℃ to 400℃; C. Reduce the temperature to room temperature at a rate of 40℃ / h below 400℃.

[0021] The beneficial effects of this invention are as follows: This device integrates the crystal growth chamber and the crystal annealing chamber into a single furnace body. Crystal growth can be performed first in the crystal growth chamber, and the grown crystal does not require cooling. It is then moved to the crystal annealing chamber for annealing and polarization operations, thus integrating growth, annealing, and polarization into a single device. This significantly improves production efficiency, saves costs, and greatly shortens the crystal annealing process cycle, thereby drastically reducing the overall production cycle. This invention not only integrates multiple lengthy steps such as cooling, transfer, reheating, and secondary cooling in traditional separate processes into a continuous flow, significantly shortening the crystal preparation cycle and increasing overall production efficiency by more than 50%, but also greatly reduces energy consumption caused by repeated heating. This provides a revolutionary solution for the efficient and energy-saving preparation of high-quality, low-stress lithium niobate crystals. Attached Figure Description

[0022] Figure 1 A schematic diagram showing the state of the seed crystal entering the crystal growth chamber; Figure 2 A schematic diagram showing the state of the crystal entering the crystal annealing chamber; Figure 3 This is a schematic diagram showing the state of the crystal separated from the pulling assembly; Figure 4 for Figure 3 Enlarged view of part A; Figure 5 for Figure 2 Side sectional view; Figure 6 for Figure 5 Enlarged view of part B; Figure 7 A schematic diagram of the seed crystal chuck and the three-dimensional structure of the seed crystal; As shown in the figure: 1. Furnace body; 101. Crystal growth chamber; 102. Crystal annealing chamber; 103. Connecting hole; 104. First heating element; 105. Second heating element; 106. First heat preservation temperature field; 107. Second heat preservation temperature field; 108. Refractory brick layer. 2. Crucible; 3. Corundum insulation container; 4. Polarization component; 41. Polarization barrel; 42. Upper electrode plate; 43. Lower electrode plate; 44. Feeding pipe; 45. First push-pull rod; 46. Polarized polycrystalline material. 5. Second push-pull rod; 6. Lifting assembly; 61. Seed crystal rod; 62. Seed crystal chuck; 7. Lifting mechanism; 70. Protective cover; 71. Vertical beam; 72. Lifting seat; 73. Support beam; 74. Fixed seat; 75. Linear drive mechanism; 751. Guide rod; 752. Sliding sleeve; 753. Lead screw; 754. Nut; 755. Second motor; 76. First motor; 77. Long strip sliding hole; 771. Heat insulation cover; 78. Guide rail; 79. Threaded rod; 791. Third motor. 8. Seed crystal. Detailed Implementation

[0023] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to describe the solution.

[0024] like Figures 1-7 As shown, an integrated production apparatus for lithium niobate single-domain crystals includes: The furnace body 1 has a crystal annealing chamber 102 and a crystal growth chamber 101 separated by upper and lower parts. The crystal annealing chamber 102 and the crystal growth chamber 101 are connected by a connecting hole 103. A plurality of first heating elements 104 are fixedly installed in the crystal growth chamber 101, and a plurality of second heating elements 105 are fixedly installed in the crystal annealing chamber 102.

[0025] like Figure 1 As shown, specifically, a horizontal partition is fixedly connected to the inner cavity of the furnace body 1, dividing the inner cavity of the furnace body 1 into a crystal annealing chamber 102 and a crystal growth chamber 101 distributed vertically. The connecting hole 103 is opened at the center of the horizontal partition, thereby connecting the crystal annealing chamber 102 and the crystal growth chamber 101. Typically, a front furnace door (not shown in the figure) is installed on the front side wall of the furnace body 1. Personnel can operate on the crystal growth chamber 101 and the crystal annealing chamber 102 by opening the front furnace door. When the front furnace door is closed, it seals the inner cavity of the furnace body 1. The front furnace door adopts the door structure of an existing clinker furnace, which is existing technology and will not be described in detail further.

[0026] Crucible 2 is used to hold lithium niobate polycrystalline material. Crucible 2 is located in crystal growth chamber 101 and is positioned opposite to the connecting hole 103. Several first heating elements 104 are distributed around the periphery of crucible 2.

[0027] like Figure 1As shown, specifically, a first heat-insulating temperature field 106 is attached to the circumferential inner wall of the crystal growth chamber 101, and a refractory brick layer 108 is laid at the bottom of the crystal growth chamber 101 to improve the heat insulation effect. In this embodiment, the first heat-insulating temperature field 106 is made of alumina fiber insulation material or ceramic fiber insulation material. A corundum heat-insulating barrel 3 is placed on the refractory brick layer 108, and the corundum heat-insulating barrel 3 is located at the center of the crystal growth chamber 101. The top of the corundum heat-insulating barrel 3 is covered with a heat-insulating cover, and a through hole is opened on the heat-insulating cover, which is arranged opposite to the connecting hole 103. In this embodiment, the first heating element 104 is a resistance silicon carbide rod, and the number of first heating elements 104 is 4 to 6. Multiple first heating elements 104 are evenly distributed circumferentially on the outside of the corundum heat-insulating barrel 3 to uniformly heat the crystal growth chamber 101. In this embodiment, the crucible 2 is a platinum crucible 2, which is placed in the corundum heat-insulating barrel 3 to further enhance the heat insulation of the system.

[0028] Polarization component 4 is used to polarize the crystal. Polarization component 4 has a polarization tank 41 for holding the lithium niobate crystal, and the polarization tank 41 is located in the crystal annealing chamber 102. Several second heating elements 105 are distributed around the polarization tank 41, and the outer diameter of the polarization tank 41 is larger than the diameter of the connecting hole 103.

[0029] A translation mechanism is used to drive the polarization barrel 41 to move horizontally so that the polarization barrel 41 opens or closes the communication hole 103. like Figure 1 As shown, specifically, a second heat-insulating temperature field 107 is attached to the circumferential inner wall of the crystal annealing chamber 102 to improve the heat insulation effect of the crystal annealing chamber 102. In this embodiment, the second heat-insulating temperature field 107 is made of zirconium oxide insulation material. In this embodiment, the second heating element 105 is also a resistance silicon carbide rod, and the number of second heating elements 105 is 4 to 6. The multiple second heating elements 105 are evenly distributed circumferentially within the second heat-insulating temperature field 107 to uniformly heat the crystal annealing chamber 102.

[0030] Specifically, the polarization barrel 41 is a corundum barrel, which is placed on a horizontal partition. The polarization barrel 41 is moved laterally by a translation mechanism. When the polarization barrel 41 and the connecting hole 103 are coaxial, the polarization barrel 41 closes the connecting hole 103. When the polarization barrel 41 moves laterally away from the connecting hole 103, the connecting hole 103 is opened.

[0031] like Figure 1 , 4As shown, the translation mechanism in this embodiment includes a second push-pull rod 5, which slides through the side wall of the crystal annealing chamber 102. The second push-pull rod 5 is fixedly connected to the polarization barrel 41 and drives the polarization barrel 41 to translate. The extension direction of the second push-pull rod 5 is the same as the translation direction of the polarization barrel 41. The second push-pull rod 5 is slidably sealed to the side wall of the crystal annealing chamber 102 through a mechanical sealing sleeve, ensuring the sealing effect between the two and reducing heat leakage. In actual use, the second push-pull rod 5 can be manually pushed. For example, a handle can be installed on the outer end of the second push-pull rod 5, allowing personnel to push and pull it. The second push-pull rod 5 can also be mechanically pushed. For example, a telescopic cylinder can be installed outside the furnace body 1, and the extension and retraction of the telescopic cylinder can drive the pushing and pulling action of the second push-pull rod 5. Depending on the actual working conditions, any pushing method can be freely selected, which will not be elaborated further here.

[0032] like Figure 4 As shown, specifically, the polarization assembly 4 includes an upper electrode plate 42, a lower electrode plate 43, a feeding pipe 44, and the polarization tank 41. The lower electrode plate 43 is disposed at the inner bottom of the polarization tank 41, and the upper electrode plate 42 is disposed at the top of the polarization tank 41, forming a polarization zone for polarizing the crystal between the upper electrode plate 42 and the lower electrode plate 43. The upper electrode plate 42 and the lower electrode plate 43 are respectively connected to the positive and negative terminals of an external power supply via platinum wires. The platinum wires are threaded through the furnace body 1 with a certain length reserved to allow sufficient slack to follow the movement of the polarization tank 41. The feeding pipe 44 is used to add polarized polycrystalline material 46 into the polarization tank 41.

[0033] Specifically, both the upper electrode 42 and the lower electrode 43 are platinum electrode sheets, which have good high-temperature resistance. The lower electrode 43 is fixed to the inner bottom of the polarization tank 41. The upper electrode 42 is slidably inserted through the side wall of the polarization tank 41, and the sliding direction of the upper electrode 42 is the same as the translation direction of the polarization tank 41. A through hole is provided in the upper part of the side wall of the polarization tank 41 for the upper electrode 42 to pass through. A first push-pull rod 45 is slidably inserted through the side wall of the crystal annealing chamber 102. The first push-pull rod 45 is fixed to the upper electrode 42 and drives the upper electrode 42 to slide.

[0034] In this embodiment, the extension direction of the first push-pull rod 45 is the same as the sliding direction of the upper electrode plate 42, and the first push-pull rod 45 is parallel to the second push-pull rod 5. The first push-pull rod 45 is sealed and slidably connected to the side wall of the crystal annealing chamber 102 through a mechanical sealing sleeve, ensuring the sealing effect between the two and reducing heat leakage. One end of the first push-pull rod 45 extends into the crystal annealing chamber 102 and is fixed to the upper electrode plate 42, while the other end is located outside the furnace body 1 for easy pushing. In actual use, the first push-pull rod 45 can be pushed manually. For example, if a handle is installed on the outer end of the first push-pull rod 45, it can be pushed and pulled by personnel. The first push-pull rod 45 can also be driven mechanically. For example, a telescopic cylinder can be set outside the furnace body 1, and the pushing and pulling action of the first push-pull rod 45 can be driven by the extension and retraction of the telescopic cylinder. Depending on the actual working conditions, any pushing method can be freely selected, which will not be elaborated on here. The upper electrode plate 42 is pushed and pulled horizontally by the first push-pull rod 45. When the upper electrode plate 42 slides outward, it will not block the top opening of the polarization barrel 41, thus facilitating the placement of the lithium niobate crystal into the polarization barrel 41 and improving ease of use. After the lithium niobate crystal is placed into the polarization barrel 41, the upper electrode plate 42 slides inward to insert into the polarization barrel 41, so that the lithium niobate crystal is located within the polarization zone, facilitating the polarization operation.

[0035] The polarization assembly 4 supplies positive and negative currents to the upper electrode plate 42 and the lower electrode plate 43 via an external power source, creating a strong electric field between them to polarize the multi-domain lithium niobate crystal. During polarization, to ensure a stable temperature field in the chamber, polarized polycrystalline material 46 is added to the polarization tank 41 via a feeding pipe 44, eliminating the need to open the front furnace door and improving ease of use. In this embodiment, the feeding pipe 44 is slidably installed on the side wall of the crystal annealing chamber 102. The feeding pipe 44 is inclined, with its lower inclined end located inside the crystal annealing chamber 102 and above the polarization tank 41. The upper inclined end of the feeding pipe 44 is located outside the furnace body 1. When the polarization tank 41 closes the connecting hole 103, the feeding pipe 44 slides into the furnace body 1, and its lower inclined end reaches directly above the polarization tank 41, thereby adding polarized polycrystalline material 46 into the polarization tank 41. When it is not necessary to add polarized polycrystalline material 46, the feeding tube 44 can be slid outward away from the polarization tank 41 without affecting the translation of the polarization tank 41 or the placement of lithium niobate crystals. The end of the feeding tube 44 located outside the furnace body 1 is detachably fitted with a sealing cap to prevent heat from dissipating from the feeding tube 44 and to enhance temperature stability.

[0036] like Figure 2 As shown, the lifting assembly 6 is used to connect the seed crystal 8. The lifting assembly 6 includes a seed crystal rod 61 and a seed crystal chuck 62. The seed crystal rod 61 is vertically inserted through the top of the furnace body 1, and the lower end of the seed crystal rod 61 is located inside the furnace body 1 and is fixedly connected to the seed crystal chuck 62.

[0037] The lifting mechanism 7 is used to drive the lifting assembly 6 to move up and down, so that the seed crystal chuck 62 can reciprocate between the crystal annealing chamber 102 and the crystal growth chamber 101 through the connecting hole 103. It is also used to drive the lifting assembly 6 to separate from the seed crystal 8.

[0038] like Figure 7 As shown, specifically, the seed crystal chuck 62 has a U-shaped structure, and the seed crystal 8 has a T-shaped structure. The cross-section of the seed crystal chuck 62 in a top view is a U-shaped structure. The cross-section of the seed crystal 8 in a front view is a T-shaped structure. The groove size of the U-shaped seed crystal chuck 62 is adapted to the outer diameter of the vertical section of the T-shaped seed crystal 8. When seed crystal rod 61 is connected to seed crystal 8, the vertical section of seed crystal 8 is inserted into the groove of seed crystal chuck 62, and the horizontal section of seed crystal 8 rests on the two protrusions of seed crystal chuck 62. The T-shaped seed crystal 8 can be vertically engaged in the groove of the U-shaped seed crystal chuck 62, allowing the seed crystal 8 to be suspended and connected to the seed crystal chuck 62, resulting in higher stability after connection. Furthermore, during annealing, the two are easier to separate, preventing heat conduction along the seed crystal chuck 62 during annealing and reducing annealing quality.

[0039] like Figure 2 , 3 As shown in Figures 5 and 6, specifically, the lifting mechanism 7 includes a vertical beam 71 fixed to the top of the furnace body 1, with a lifting seat 72 slidably mounted on one side of the vertical beam 71. A supporting crossbeam 73 is fixed to one side of the lifting seat 72, and a fixed seat 74 is slidably mounted on the bottom of the supporting crossbeam 73. A linear drive mechanism 75 for driving the fixed seat 74 to slide horizontally is provided on the supporting crossbeam 73. A first motor 76 is mounted on the fixed seat 74, with the output shaft of the first motor 76 facing downwards. An elongated sliding hole 77 is opened at the top of the furnace body 1, and the upper end of the seed crystal rod 61 passes through the elongated sliding hole 77 and is fixedly connected to the output shaft of the first motor 76.

[0040] It should be noted that the extension direction of the elongated sliding hole 77 is the same as the horizontal sliding direction of the fixing seat 74, that is, the same as the translational direction of the seed crystal rod 61. The width of the elongated sliding hole 77 is adapted to the outer diameter of the seed crystal rod 61, and the length is preferably 3~5cm, which is sufficient to allow the lifting assembly 6 to move horizontally and detach from the lithium niobate crystal, so as to minimize heat loss. Since the size of the elongated sliding hole 77 is small, the heat dissipation effect is minimal and does not affect the temperature stability inside the crystal annealing cavity.

[0041] Preferably, a heat insulation cover 771 is fitted onto the seed crystal rod 61. The heat insulation cover 771 is located on top of the furnace body 1 and covers the elongated sliding hole 77. The covering area of ​​the heat insulation cover 771 is larger than the diameter of the elongated sliding hole 77. When the heat insulation cover 771 moves horizontally with the seed crystal rod 61, it can still cover the elongated sliding hole 77, ensuring the stability of the internal temperature field. The heat insulation cover 771 is made of ceramic fiber material. In use, the heat insulation cover is fitted onto the seed crystal rod and placed on top of the furnace body, thereby sealing the elongated sliding hole. This does not affect the movement of the seed crystal rod and also prevents heat from escaping.

[0042] In this embodiment, two fixing plates are fixedly connected to one side of the upright beam 71, with the two fixing plates distributed vertically. A vertical guide rail 78 is fixed between the two fixing plates, and the lifting seat 72 is slidably connected to the guide rail 78 to achieve the vertical sliding effect of the lifting seat 72. A threaded rod 79 is rotatably installed between the two fixing plates, passing through the lifting seat 72, and the lifting seat 72 is threadedly connected to the threaded rod 79. A third motor 791 is fixedly connected to the fixing plates, and the output end of the third motor 791 is fixedly connected to one end of the threaded rod 79. The third motor 791 drives the threaded rod 79 to rotate, thereby causing the threaded lifting seat 72 to rise and fall along the guide rail 78, which in turn drives the support beam 73 to rise and fall, causing the lifting assembly 6 to move vertically.

[0043] Preferably, a protective cover 70 is also fixedly installed on the top of the furnace body 1, and the supporting cross plate extends into the protective cover 70. An opening is provided on the side wall of the protective cover 70 near the vertical beam 71 for the supporting cross plate to slide up and down. A guide rail 78 is also fixedly connected to the side wall of the protective cover 70 away from the vertical beam 71, and the end of the supporting cross beam 73 away from the vertical beam 71 is slidably connected to the guide rail 78 to improve stability during sliding. The fixed base 74, the linear drive mechanism 75, and the first motor 76 are all located inside the protective cover 70 and protected by the protective cover 70.

[0044] The linear drive mechanism 75 described in this embodiment is a lead screw 753 and nut 754 assembly. A guide rod 751 is fixedly mounted on the bottom surface of the supporting beam 73. The guide rod 751 extends along the length of the supporting beam 73 and is parallel to the supporting beam 73. A sliding sleeve 752 is fitted on the guide rod 751. The fixed seat 74 is fixedly connected to the sliding sleeve 752, thereby achieving a sliding connection with the supporting beam 73. The lead screw 753 and nut 754 assembly includes a lead screw 753, a nut 754, and a second motor 755. The lead screw 753 is rotatably mounted on the bottom surface of the supporting beam 73, extending along the length of the supporting beam 73 and parallel to the guide rod 751. The nut 754 is screwed onto the lead screw 753, and the fixed seat 74 and nut 754 are fixedly connected. The second motor 755 is fixed to the bottom of the supporting beam 73 and drives the lead screw 753 to rotate. The second motor 755 drives the lead screw 753 to rotate, causing the nut 754 to move along the lead screw 753. With the guidance of the guide rod 751, the fixed seat 74 drives the first motor 76 to move horizontally, thereby causing the lifting assembly 6 to move horizontally. The lead screw 753 and nut 754 pair is a commonly used linear drive mechanism 75, which will not be described in detail here.

[0045] The lifting mechanism 7 drives the lifting seat 72 to slide up and down, causing the lifting assembly 6 to rise and fall, thus allowing the seed crystal chuck 62 to reciprocate between the crystal annealing chamber 102 and the crystal growth chamber 101. The first motor 76 drives the lifting assembly 6 to rotate, which can be used for rotational lifting during crystal growth. When it is necessary to separate the lifting assembly 6 from the seed crystal 8, the linear drive mechanism 75 drives the lifting assembly 6 to move horizontally, causing the U-shaped seed crystal chuck 62 to move laterally away from the T-shaped seed crystal 8. The vertical section of the T-shaped seed crystal 8 disengages from the groove of the seed crystal chuck 62, and then the telescopic cylinder drives the lifting assembly 6 to move upward, thus achieving the separation of the lifting assembly 6 from the crystal.

[0046] A method for producing the above-mentioned lithium niobate single-domain crystal using the aforementioned production apparatus includes the following steps: S1. Prepare lithium niobate polycrystalline material: Place the lithium niobate polycrystalline material, which is made by mixing and sintering lithium carbonate and niobium oxide raw materials, in crucible 2, and suspend seed crystal 8 on seed crystal chuck 62 of lifting component 6. In step S1, lithium carbonate and niobium oxide raw materials are mixed in a certain molar ratio, and then pre-calcined, intensified mixing and secondary calcination are performed to synthesize lithium niobate polycrystalline material. This is a conventional process for preparing lithium niobate polycrystalline material and can be prepared in advance. During operation, personnel can open the front furnace door, put the pre-prepared lithium niobate polycrystalline material into crucible 2, and suspend the seed crystal 8 on the seed crystal chuck 62.

[0047] S2. Crystal growth: The crystal growth chamber 101 is heated by the first heating element 104, which melts the lithium niobate polycrystalline material into liquid polycrystalline material; the lifting mechanism 7 drives the lifting assembly 6 to descend, so that the seed crystal 8 moves to the crystal growth chamber 101, and the crystal is grown by the lifting method. After seeding, necking, shouldering, constant diameter growth, tailing, and pulling, lithium niobate multidomain crystal is obtained. In step S2, during the crystal growth stage, the polarization tank 41 opens the connecting hole 103, so that the crystal growth chamber 101 and the crystal annealing chamber 102 are in a connected state; the first heating element 104 heats the crystal growth chamber 101 to maintain it at the crystal growth temperature (around 1240℃), and the first heating element 104 heats at a heating rate of 20~30℃ / h; since the crystal growth chamber 101 and the crystal annealing chamber 102 are connected, the heat from the crystal growth chamber 101 will diffuse to the crystal annealing chamber 102 for preheating, thereby improving the heating efficiency during annealing.

[0048] S3. Annealing heating: After the lithium niobate multidomain crystal is made, it is not cooled down, but is kept warm in the crystal growth chamber 101. At the same time, it is heated by the second heating element 105, so that the crystal annealing chamber 102 is heated and maintained at the annealing temperature. In step S3, the second heating element 105 is heated at a heating rate of 20~30℃ / h, and the annealing temperature of the crystal annealing chamber 102 is 1200℃.

[0049] S4. Crystal Annealing: The lifting mechanism 7 drives the lifting assembly 6 to rise, moving the uncooled lithium niobate multidomain crystal to the crystal annealing chamber 102; the translation mechanism drives the polarization barrel 41 to move horizontally, causing the polarization barrel 41 to close the connecting hole 103; the lifting mechanism 7 drives the lifting assembly 6 to fall, placing the lithium niobate multidomain crystal in the polarization barrel 41; the lifting mechanism 7 drives the seed crystal chuck 62 of the lifting assembly 6 to separate from the lithium niobate multidomain crystal; the lithium niobate multidomain crystal is kept at the annealing temperature to complete the hot annealing operation and release the crystal thermal stress; In step S4, the annealing temperature of the crystal annealing chamber 102 is 1200℃, and the holding time is 9.5~10h.

[0050] S5. Crystal Polarization: After annealing, the lithium niobate multidomain crystal is added to the polarization tank 41 through the feeding pipe 44, so that the lithium niobate multidomain crystal is embedded in the polarization polycrystalline material 46; an external power supply is used to pass current through the upper electrode plate 42 and the lower electrode plate 43 to apply polarization current to the lithium niobate multidomain crystal; the current is kept on for a certain period of time to perform polarization operation on the lithium niobate multidomain crystal; then the annealing temperature is cooled down to below the crystal Curie temperature and the current is removed to obtain a lithium niobate single-domain crystal; In step S5, the polarization current density of the lithium niobate multidomain crystal is 2~3 mA / cm². 2The external power supply is gradually applied to the polarization current at a rate of 1~2mA / min; after the polarization current is applied, it is held for 30~60min; the annealing temperature is reduced to 1100℃ at a rate of 15℃ / h, and then the current is removed at 1~2mA / min.

[0051] S6. Cool the lithium niobate single-domain crystal to room temperature in a stepwise manner. The stepwise cooling procedure in step S6 is as follows: A. Cooling rate of 20℃ / h from 1100℃ to 800℃; B. Cooling down at 30℃ / h from 800℃ to 400℃; C. Reduce the temperature to room temperature at a rate of 40℃ / h below 400℃.

[0052] This method integrates growth, annealing, and polarization into a single device. Since no external transfer is required during operation, the grown crystal does not need to be cooled or heated again before annealing, thus greatly shortening the annealing process cycle and significantly reducing the overall production cycle.

[0053] The following is a detailed example: (1) Lithium niobate polycrystalline material was synthesized by high-temperature sintering of lithium carbonate and niobium oxide raw materials with a solid-liquid isotropic ratio (molar ratio 48.38 / 51.62). The synthesized lithium niobate polycrystalline material was placed in a platinum crucible 2, and the seed crystal 8 was suspended and connected to the seed crystal chuck 62.

[0054] (2) The first heating element 104 is set to heat the crystal growth chamber 101 at a heating rate of 30℃ / h, so that the crystal growth chamber 101 reaches the growth temperature of 1240℃ (about 50℃ higher than the melting point of lithium niobate polycrystalline material) and is maintained. The temperature is kept constant for 3 hours to melt the lithium niobate polycrystalline material into liquid lithium niobate polycrystalline material.

[0055] (3) The telescopic cylinder extends, causing the suspended seed crystal 8 to slowly descend into the crystal growth chamber 101 at a speed of 10 mm / min, and the seed crystal 8 contacts the liquid surface of the liquid lithium niobate polycrystalline material to form a stable solid-liquid interface. Using the Czochralski method, after seeding, necking, shouldering, constant diameter growth, and tailing, a lithium niobate multidomain crystal is obtained. After the growth is completed, the lithium niobate multidomain crystal is pulled off at a rate of 20 mm / min to complete the crystal growth process.

[0056] (4) No cooling is performed after crystal growth. A second heating element 105 is set up to heat the crystal annealing chamber 102 at a heating rate of 20℃ / h, so that the crystal annealing chamber 102 reaches the annealing temperature of 1200℃ and is maintained. After the temperature stabilizes, the telescopic cylinder retracts to lift the uncooled lithium niobate multidomain crystal to the heated crystal annealing chamber 102 at a speed of 20 mm / h. The polarization barrel 41 is pushed by the second push-pull rod 5 to move horizontally below the lithium niobate multidomain crystal at a speed of 20 mm / min, while sealing the connecting hole 103.

[0057] (5) A portion of the polarized polycrystalline material 46 is added to the polarization tank 41 through the feeding pipe 44 to cover the lower electrode sheet 43. The telescopic cylinder extends, lowering the lithium niobate multidomain crystal into the polarization tank 41 at a speed of 10 mm / min, so that the lithium niobate multidomain crystal is placed on the polarized polycrystalline material 46. The lifting assembly 6 is driven to move horizontally 100 mm relative to the seed crystal 8 by the linear drive mechanism 75, so that the lifting assembly 6 is separated from the seed crystal 8. Then the telescopic cylinder retracts, causing the lifting assembly 6 to be rapidly raised 150 mm, so that the lifting assembly 6 is away from the lithium niobate multidomain crystal. The lithium niobate multidomain crystal is held at 1200℃ for 10 h to complete the thermal annealing operation, release the thermal stress of the crystal, and continue the polarization operation.

[0058] (6) After annealing, continue adding polarized polycrystalline material 46 into the polarization tank 41 through the feeding pipe 44, so that the polarized polycrystalline material 46 fills the polarization tank 41, thereby covering the lithium niobate multidomain crystal. Push the upper electrode plate 42 to slide and press it against the upper end of the polarized polycrystalline material 46 through the first push-pull rod 45. Control the external power supply to slowly apply current to the electrode plate at 1 mA / min, and adjust the current according to the crystal size at 2 mA / cm. 2 A current (e.g., 100 mA for a 3-inch lithium niobate crystal) is applied and kept energized for 30 min to perform polarization. Then, the temperature is reduced to 1100 °C at a rate of 15 °C / h, and the current is removed at 1 mA / min to complete the polarization, yielding a lithium niobate single-domain crystal.

[0059] (6) Finally, a stepped cooling procedure was used: A. 1100℃~800℃, cooling at 20℃ / h for 15h; B. 800℃~400℃, cooling at 30℃ / h for 13.5h; C. Below 400℃, cooling at 40℃ / h to room temperature (25℃) for 9.5h, completing the in-situ thermal annealing and polarization operation, obtaining a stress-uniform single-domain crystal, and removing the lithium niobate single-domain crystal. This achieves an integrated preparation operation of lithium niobate crystal growth, thermal annealing, and polarization.

[0060] Using a method for producing 8-inch lithium niobate crystals disclosed in patent CN 111206282A as a comparative example, the annealing process of this patent is as follows: heating from 30℃ to 200℃ for 170~190min, heating from 200℃ to 1100℃ for 1070~1090min, heating from 1100℃ to 1230℃±5℃ for 390~410min; holding time for 550~650min; cooling to 1170℃±10℃ for 170~190min, holding for 230~250min, cooling to 950℃ for 1650~1750min, and cooling to 600℃ for 410~430min.

[0061] It is known that this annealing process, starting from room temperature (30℃) and then heating to 1230℃ for a second heating, takes 27-29 hours. In addition, after crystal growth, it needs to be cooled to room temperature and undergo a certain period of stress release before it can be removed for the aforementioned second heating, resulting in a long production cycle.

[0062] The crystals of this invention do not require cooling or secondary heating after growth. Because the process is continuous within a single growth apparatus, the grown crystals are directly and slowly pulled into the crystal annealing chamber 102 for annealing-polarization. This significantly reduces cycle time and improves annealing quality, reduces stress, and decreases the crystal cracking rate.

[0063] Of course, the above description is not limited to the examples above. Technical features not described in this invention can be implemented by or using existing technology, and will not be repeated here. The above embodiments and drawings are only used to illustrate the technical solutions of this invention and are not intended to limit this invention. This invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention do not depart from the spirit of this invention and should also fall within the scope of protection of the claims of this invention.

Claims

1. An integrated production apparatus for lithium niobate single-domain crystals, characterized in that, include: The furnace body (1) has a crystal annealing chamber (102) and a crystal growth chamber (101) that are separated into upper and lower parts. The crystal annealing chamber (102) and the crystal growth chamber (101) are connected through a connecting hole (103). A number of first heating elements (104) are fixedly installed in the crystal growth chamber (101), and a number of second heating elements (105) are fixedly installed in the crystal annealing chamber (102). The crucible (2) is located in the crystal growth chamber (101) and is opposite to the connecting hole (103). Several first heating elements (104) are distributed around the crucible (2). The polarization component (4) is used to polarize the crystal. The polarization component (4) has a polarization barrel (41) for holding the crystal. The polarization barrel (41) is located in the crystal annealing chamber (102). Several second heating elements (105) are distributed around the polarization barrel (41). The outer diameter of the polarization barrel (41) is larger than the diameter of the connecting hole (103). Translation mechanism is used to drive the polarization barrel (41) to move horizontally so that the polarization barrel (41) opens or closes the connecting hole (103). The lifting assembly (6) is used to connect the seed crystal (8). The lifting assembly (6) includes a seed crystal rod (61) and a seed crystal chuck (62). The seed crystal rod (61) is vertically inserted through the top of the furnace body (1). The lower end of the seed crystal rod (61) is located inside the furnace body (1) and is fixedly connected to the seed crystal chuck (62). The lifting mechanism (7) is used to drive the lifting assembly (6) to rise and fall so that the seed crystal chuck (62) passes through the connecting hole (103) and moves back and forth between the crystal annealing chamber (102) and the crystal growth chamber (101), and is also used to drive the lifting assembly (6) to separate from the seed crystal (8).

2. The integrated production apparatus for lithium niobate single-domain crystals according to claim 1, characterized in that: The polarization assembly (4) includes an upper electrode plate (42), a lower electrode plate (43), a feeding tube (44), and the polarization tank (41). The lower electrode plate (43) is disposed at the bottom of the polarization tank (41), and the upper electrode plate (42) is disposed at the top of the polarization tank (41). A polarization zone for polarizing crystals is formed between the upper electrode plate (42) and the lower electrode plate (43). The upper electrode plate (42) and the lower electrode plate (43) are respectively connected to the positive and negative terminals of an external power supply through platinum wires. The feeding tube (44) is used to add polarized polycrystalline material (46) into the polarization tank (41).

3. The integrated production apparatus for lithium niobate single-domain crystals according to claim 2, characterized in that: The upper electrode plate (42) is slidably disposed on the side wall of the polarization barrel (41). The sliding direction of the upper electrode plate (42) is the same as the translation direction of the polarization barrel (41). A first push-pull rod (45) is slidably disposed on the side wall of the crystal annealing chamber (102). The first push-pull rod (45) is fixedly connected to the upper electrode plate (42) and drives the upper electrode plate (42) to slide.

4. The integrated production apparatus for lithium niobate single-domain crystals according to claim 1, characterized in that: The translation mechanism includes a second push-pull rod (5), which slides through the side wall of the crystal annealing chamber (102). The second push-pull rod (5) is fixed to the polarization barrel (41) and drives the polarization barrel (41) to translate.

5. The integrated production apparatus for lithium niobate single-domain crystals according to claim 1, characterized in that: The seed crystal chuck (62) has a concave shape, and the seed crystal (8) has a T-shaped structure.

6. The integrated production apparatus for lithium niobate single-domain crystals according to claim 5, characterized in that: The lifting mechanism (7) includes a vertical beam (71) fixed to the top of the furnace body (1), a lifting seat (72) is slidably installed on one side of the vertical beam (71), a supporting crossbeam (73) is fixedly installed on one side of the lifting seat (72), a fixed seat (74) is slidably installed at the bottom of the supporting crossbeam (73), a linear drive mechanism (75) for driving the fixed seat (74) to slide horizontally is provided on the supporting crossbeam (73), a first motor (76) is installed on the fixed seat (74), the output shaft of the first motor (76) faces downward, a long sliding hole (77) is opened at the top of the furnace body (1), the upper end of the seed crystal rod (61) passes through the long sliding hole (77) and is fixedly connected to the output shaft of the first motor (76).

7. The production method of the lithium niobate single-domain crystal production apparatus according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Prepare lithium niobate polycrystalline material: Place the lithium niobate polycrystalline material, which is made by mixing and sintering lithium carbonate and niobium oxide raw materials, into a crucible (2), and suspend the seed crystal (8) on the seed crystal chuck (62) of the lifting assembly (6). S2. Crystal growth: The crystal growth chamber (101) is heated by the first heating element (104) to melt the lithium niobate polycrystalline material into liquid polycrystalline material; the lifting mechanism (7) drives the lifting assembly (6) to descend, so that the seed crystal (8) moves to the crystal growth chamber (101) and the crystal is grown by the lifting method. After seeding, necking, shouldering, equal diameter growth, tailing and pulling, lithium niobate multidomain crystal is obtained. S3, Annealing heating: After the lithium niobate multidomain crystal is made, it is not cooled down, but is kept warm in the crystal growth chamber (101). At the same time, it is heated by the second heating element (105) to raise the temperature of the crystal annealing chamber (102) and maintain it at the annealing temperature. S4, Crystal Annealing: The lifting mechanism (7) drives the lifting assembly (6) to rise, moving the uncooled lithium niobate multidomain crystal to the crystal annealing chamber (102); the translation mechanism drives the polarization barrel (41) to move horizontally, so that the polarization barrel (41) closes the connecting hole (103); the lifting mechanism (7) drives the lifting assembly (6) to fall, placing the lithium niobate multidomain crystal in the polarization barrel (41); the lifting mechanism (7) drives the seed crystal chuck (62) of the lifting assembly (6) to separate from the lithium niobate multidomain crystal; the lithium niobate multidomain crystal is kept at the annealing temperature to complete the hot annealing operation and release the crystal thermal stress; S5. Crystal polarization: After annealing, the lithium niobate multidomain crystal is added to the polarization tank (41) through the feeding tube (44) to embed the lithium niobate multidomain crystal in the polarization polycrystalline material (46); the external power supply passes current through the upper electrode plate (42) and the lower electrode plate (43) to apply polarization current to the lithium niobate multidomain crystal; the current is kept on for a certain period of time to perform polarization operation on the lithium niobate multidomain crystal; then the annealing temperature is cooled to below the crystal Curie temperature and the current is removed to obtain a lithium niobate single-domain crystal; S6. Cool the lithium niobate single-domain crystal to room temperature in a stepwise manner.

8. The production method of the lithium niobate single-domain crystal production apparatus according to claim 7, characterized in that: In step S4, the annealing temperature of the crystal annealing chamber (102) is 1200℃, and the holding time is 9.5~10h.

9. The production method of the lithium niobate single-domain crystal production apparatus according to claim 7, characterized in that: In step S5, the polarization current density of the lithium niobate multidomain crystal is 2~3 mA / cm². 2 The external power supply is gradually applied to the polarization current at a rate of 1~2mA / min; after the polarization current is applied, it is held for 30-60min; the annealing temperature is reduced to 1100℃ at a rate of 15℃ / h, and then the current is removed at 1~2mA / min.

10. The production method of the lithium niobate single-domain crystal production apparatus according to claim 7, characterized in that, In step S6, the stepped cooling procedure is as follows: A. Cooling rate of 20℃ / h from 1100℃ to 800℃; B. Cooling down at 30℃ / h from 800℃ to 400℃; C. Reduce the temperature to room temperature at a rate of 40℃ / h below 400℃.

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