Preparation method of large-size lithium niobate crystal

Abstract

The invention belongs to the technical field of piezoelectric crystals, and particularly discloses a preparation method of a large-size lithium niobate crystal, which comprises the following steps: mounting a seed crystal bar on a seed crystal rod, putting a platinum crucible into a corundum crucible placed in a single crystal growth furnace temperature field, putting a blocky polycrystal raw material into the platinum crucible, and uniformly stirring, thereby obtaining the large-size lithium niobate crystal. Raising the temperature to melt the polycrystal material into a polycrystal melt, then lowering the seed rod to be in contact with the surface of the polycrystal melt, lifting the seed rod for seeding after the head of the seed rod is semi-molten, and then carrying out necking, heat preservation and automatic growth; after the crystal grows to a preset length, adjusting the temperature for ending, lifting the crystal to be separated from the liquid level, and annealing; therefore, the large-size lithium niobate crystal with standard form and completely consistent components at the head and the tail of the crystal is prepared.

Description

Technical Field

[0001] The invention relates to the technical field of piezoelectric crystals, and in particular to a method for preparing a large-sized lithium niobate crystal. Background Art

[0002] With the rapid development of the information age, we have entered an era of digitalization, intelligence, and informatization. Industries such as cloud computing, artificial intelligence, video conferencing, short videos, and various social media are booming. The AI ​​era has also arrived, and the demand for high-frequency and multi-band communications has increased significantly. At the same time, higher requirements have been placed on transmission rate and capacity.

[0003] Lithium niobate [LN] crystals have multiple physical properties such as piezoelectric effect, pyroelectric effect, electro-optic effect, and acousto-optic effect. They are widely used in surface acoustic wave (SAW) devices, optoelectronic devices, etc., especially in surface acoustic wave (SAW) devices. In recent years, with the emergence of lithium niobate [LN] single crystal thin film technology, the application of lithium niobate [LN] crystals has become more extensive. As the basic material for surface acoustic wave filters and optical communications, the market demand for lithium niobate [LN] crystals will also increase significantly.

[0004] The current lithium niobate [LN] crystals in China are mainly 4 inches, supplemented by 6 inches, and the growth technology of 8-inch crystals is not yet mature. The growth of lithium niobate [LN] crystals is mainly prepared by Cz technology (Czech method), that is, after putting down the seed crystal rod, the seed crystal rod is slowly rotated and pulled to complete the crystal seeding, and then the pulling rate is changed to shrink the neck, release the shoulder, and then grow with equal diameter, and finally end the tail to complete the growth of the entire single crystal rod; for the growth of large-sized [6, 8-inch] lithium niobate crystals, due to the large diameter of the crystal, the radial temperature gradient increases compared with the small-sized crystal, and the crystallization amount also increases at the same lifting rate, the weight of the melt in the crucible changes rapidly, which is easy to affect the axial temperature gradient. The comprehensive results are: polycrystalline crystals, easy to crack, easy to have irregular morphology, and the components of the head and tail of the crystal are not completely consistent.

[0005] In view of this, this application is filed. Summary of the invention

[0006] The invention provides a method for preparing a large-sized lithium niobate crystal, and a large-sized lithium niobate crystal with a standardized morphology and completely consistent components at the head and tail of the crystal is prepared.

[0007] The present invention solves the technical problem by adopting the following technical solutions: A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) mixing niobium oxide and lithium carbonate uniformly to obtain a first mixture; adding the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol to water, stirring uniformly to obtain a mixed solution, drying the mixed solution, pressing it into a block, and sintering to obtain a block polycrystalline raw material; (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, heat up to melt the polycrystalline material into polycrystalline melt, then lower the seed crystal rod to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod for seeding, and then shrink the neck and keep the temperature to enter automatic growth; (4) When the crystal grows to a preset length, the temperature is adjusted to finish the process, the crystal is pulled out of the liquid surface, and annealed to obtain a large-sized lithium niobate crystal.

[0008] As a preferred embodiment of the present invention, the molar ratio of niobium oxide to lithium carbonate is (51-52): (48-49).

[0009] As a preferred embodiment of the present invention, the mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1: (0.01-0.03): (0.03-0.06): (0.02-0.05):: (0.01-0.02): (0.5-2): (4-10).

[0010] As a preferred embodiment of the present invention, the sintering temperature is 850-950° C., and the sintering time is 6-10 hours.

[0011] As a preferred embodiment of the present invention, the heating rate is 8-15°C / min.

[0012] As a preferred embodiment of the present invention, the rate of descending the seed crystal rod is 2-6 mm / min; The rate of lifting the seed crystal rod for seeding is 0.5-1 mm / min.

[0013] As a preferred embodiment of the present invention, the necking is reduced to 2-3 mm.

[0014] As a preferred embodiment of the present invention, the preset length is 200-300 mm.

[0015] As a preferred embodiment of the present invention, the annealing temperature is 1200-1250°C.

[0016] As a preferred embodiment of the present invention, the rate of pulling the crystal away from the liquid surface is 4-10 mm / min.

[0017] The beneficial effects of the present invention are as follows: the present invention installs a seed crystal rod on a seed crystal rod, places a platinum crucible into a corundum crucible placed in a temperature field of a single crystal growth furnace, places a block of polycrystalline raw material into the platinum crucible, heats up to melt the polycrystalline material into a polycrystalline melt, then lowers the seed crystal rod to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half-melted, lifts the seed crystal rod to seed the crystal; when the crystal grows to a preset length, adjusts the temperature to finish, pulls the crystal out of the liquid surface, and anneals to reduce the axial temperature gradient of the large-sized lithium niobate crystal during in-situ annealing. In-situ annealing can improve production efficiency and reduce the risk of cracking of the crystal when it is out of the furnace; reduces the radial temperature gradient at the bottom, reduces the bottom concave of the crystal when it is pulled off at the end, thereby reducing the bottom stress of the large-sized lithium niobate crystal, and also reduces the risk of crystal cracking, thereby preparing a large-sized lithium niobate crystal with a standardized morphology and completely consistent components at the head and tail of the crystal. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0020] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0021] In the present invention, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0022] The reagents or instruments used in the present invention without indicating the manufacturer are all conventional products that can be obtained commercially. The raw materials used in the comparative examples and the raw materials used in the parallel experiments of the embodiments are the same commercially available products unless otherwise specified.

[0023] The present application embodiment provides a method for preparing a large-sized lithium niobate crystal, comprising the following steps: (1) mixing niobium oxide and lithium carbonate uniformly to obtain a first mixture; adding the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol to water, stirring uniformly to obtain a mixed solution, drying the mixed solution, pressing it into a block, and sintering to obtain a block polycrystalline raw material; (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, heat up to melt the polycrystalline material into polycrystalline melt, then lower the seed crystal rod to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod for seeding, and then shrink the neck and keep the temperature to enter automatic growth; (4) When the crystal grows to a preset length, the temperature is adjusted to finish the process, the crystal is pulled out of the liquid surface, and annealed to obtain a large-sized lithium niobate crystal.

[0024] In one embodiment, the molar ratio of niobium oxide to lithium carbonate is (51-52): (48-49).

[0025] In one embodiment, the mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol, and water is 1: (0.01-0.03): (0.03-0.06): (0.02-0.05):: (0.01-0.02): (0.5-2): (4-10).

[0026] In one embodiment, the sintering temperature is 850-950° C., and the sintering time is 6-10 hours.

[0027] In one embodiment, the heating rate is 8-15°C / min.

[0028] In one embodiment, the rate of descending the seed crystal rod is 2-6 mm / min; The rate of lifting the seed crystal rod for seeding is 0.5-1 mm / min.

[0029] In one embodiment, the necking is to 2-3 mm.

[0030] In one embodiment, the preset length is 200-300 mm.

[0031] In one embodiment, the annealing temperature is 1200-1250°C.

[0032] In one embodiment, the rate of pulling the crystal away from the liquid surface is 4-10 mm / min.

[0033] Example 1 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.02:0.05:0.04:0.015:1:6.

[0034] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0035] Example 2 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.01:0.03:0.05:0.02:0.5:10.

[0036] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0037] Example 3 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.03:0.06:0.02:0.01:2:4.

[0038] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) installing the seed crystal rod on the seed crystal rod, placing the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, placing the block polycrystalline raw material into the platinum crucible, and heating the temperature to 1280°C at a rate of 10°C / min to melt the polycrystalline material into a polycrystalline melt. During the heat preservation, the temperature of the seed crystal rod is gradually reduced from top to bottom, with a reduction gradient of 10°C / dm, and the temperature of the uppermost end of the seed crystal rod is 1180°C; Then the seed crystal rod is lowered at a rate of 5 mm / min to contact the surface of the polycrystalline melt. After the head of the seed crystal rod is half melted, the seed crystal rod is lifted at a rate of 1 mm / min for seeding. After the neck is reduced to 2 mm, the temperature is kept to enter automatic growth. (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0039] Example 4 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.02:0.05:0.04:0.015:1:6.

[0040] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) installing the seed crystal rod on the seed crystal rod, placing the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, placing the block polycrystalline raw material into the platinum crucible, and heating the temperature to 1280°C at a rate of 8°C / min to melt the polycrystalline material into a polycrystalline melt. During the heat preservation, the temperature of the seed crystal rod is gradually reduced from top to bottom, and the reduction gradient is 8°C / dm. The temperature of the uppermost end of the seed crystal rod is 1180°C; Then the seed crystal rod is lowered at a rate of 6 mm / min to contact the surface of the polycrystalline melt. After the head of the seed crystal rod is half melted, the seed crystal rod is lifted at a rate of 1 mm / min for seeding. After the neck is reduced to 2 mm, the temperature is kept to enter automatic growth. (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 6 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0041] Example 5 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.02:0.05:0.04:0.015:1:6.

[0042] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) installing the seed crystal rod on the seed crystal rod, placing the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, placing the block polycrystalline raw material into the platinum crucible, and heating the temperature to 1280°C at a rate of 15°C / min to melt the polycrystalline material into a polycrystalline melt. During the heat preservation, the temperature of the seed crystal rod is gradually reduced from top to bottom, with a reduction gradient of 5°C / dm, and the temperature of the uppermost end of the seed crystal rod is 1180°C; Then the seed crystal rod is lowered at a rate of 2 mm / min to contact the surface of the polycrystalline melt. After the head of the seed crystal rod is half melted, the seed crystal rod is lifted at a rate of 1 mm / min for seeding. After the neck is reduced to 2 mm, the temperature is kept to enter automatic growth. (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 2 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0043] Comparative Example 1 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.02:0.05:0.015:1:6.

[0044] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0045] Comparative Example 2 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.02:0.04:0.015:1:6.

[0046] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0047] Comparative Example 3 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, zinc nitrate, magnesium nitrate, anhydrous ethanol and water is 1:0.02:0.05:0.04:0.015:1:6.

[0048] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0049] Comparative Example 4 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, aluminum nitrate, ferric nitrate, anhydrous ethanol and water is 1:0.02:0.05:0.04:0.015:1:6.

[0050] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0051] Comparative Example 5 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.02:0.005:0.085:0.015:1:6.

[0052] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0053] Comparative Example 6 A method for preparing a large-sized lithium niobate crystal comprises the following steps: (1) Niobium oxide and lithium carbonate are mixed uniformly in a molar ratio of 51.4:48.6 to obtain a first mixture, the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol are added to water, and stirred uniformly at 65° C. to obtain a mixed solution, the mixed solution is dried, pressed into a block, and sintered at 900° C. for 8 hours to obtain a block polycrystalline raw material; The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1:0.02:0.085:0.005:0.015:1:6.

[0054] (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four surfaces along the length direction, marking defective parts through optical detection, and cutting and removing the defective parts to obtain a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, and heat it to 1280℃ at a rate of 10℃ / min to melt the polycrystalline material into a polycrystalline melt, then lower the seed crystal rod at a rate of 5 mm / min to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod at a rate of 1 mm / min for seeding, and then shrink it to 2mm and keep it warm to enter automatic growth; (4) When the crystal grows to a preset length of 200 mm, the temperature is adjusted to finish the growth, and the crystal is pulled out of the liquid surface at a rate of 5 mm / min and annealed to obtain a large-sized lithium niobate crystal.

[0055] Test Case The photorefractive performance is tested using a dual-wave coupling experiment.

[0056] Table 1

[0057] It can be seen from Table 1 that the modified lithium niobate crystal of the present invention has excellent diffraction efficiency and photorefractive sensitivity.

[0058] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing large-sized lithium niobate crystals, characterized in that: The following steps are involved: (1) mixing niobium oxide and lithium carbonate uniformly to obtain a first mixture; adding the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, and anhydrous ethanol to water, stirring uniformly to obtain a mixed solution, drying the mixed solution, pressing it into a block, and sintering to obtain a block polycrystalline raw material; (2) Cutting the blocky polycrystalline raw material into rectangular strips, polishing the four sides along the length direction, marking the defective parts through optical inspection, and cutting and removing the defective parts; Obtaining a seed crystal rod; (3) Install the seed crystal rod on the seed crystal rod, place the platinum crucible into the corundum crucible placed in the temperature field of the single crystal growth furnace, place the block polycrystalline raw material into the platinum crucible, heat up to melt the polycrystalline material into polycrystalline melt, then lower the seed crystal rod to contact the surface of the polycrystalline melt, and after the head of the seed crystal rod is half melted, lift the seed crystal rod for seeding, and then shrink the neck and keep the temperature to enter automatic growth; (4) When the crystal grows to a preset length, the temperature is adjusted to finish the process, the crystal is pulled out of the liquid surface, and annealed to obtain a large-sized lithium niobate crystal.

2. The method for preparing large-size lithium niobate crystals according to claim 1, characterized in that: The molar ratio of niobium oxide to lithium carbonate is (51-52): (48-49).

3. The method for preparing large-size lithium niobate crystals according to claim 1, characterized in that: The mass ratio of the first mixture, sodium dodecylbenzene sulfonate, citric acid, lanthanum nitrate, cerium nitrate, anhydrous ethanol and water is 1: (0.01-0.03): (0.03-0.06): (0.02-0.05):: (0.01-0.02): (0.5-2): (4-10).

4. The method for preparing large-size lithium niobate crystals according to claim 1, characterized in that: The sintering temperature is 850-950° C., and the sintering time is 6-10 hours.

5. The method for preparing large-sized lithium niobate crystals according to claim 1, characterized in that: The heating rate is 8-15°C / min.

6. The method for preparing large-sized lithium niobate crystals according to claim 1, characterized in that: The rate of descending the seed crystal rod is 2-6 mm / min; The rate of lifting the seed crystal rod for seeding is 0.5-1 mm / min.

7. The method for preparing large-sized lithium niobate crystals according to claim 1, characterized in that: Neck down to 2~3mm.

8. The method for preparing large-size lithium niobate crystals according to claim 1, characterized in that: The preset length is 200~300mm.

9. The method for preparing large-sized lithium niobate crystals according to claim 1, characterized in that: The annealing temperature is 1200~1250℃.

10. The method for preparing large-sized lithium niobate crystals according to claim 1, characterized in that: The rate of pulling the crystal away from the liquid surface is 4-10 mm / min.

Images