Double-crucible real-time feeding growth method for potassium tantalate niobate crystals

Abstract

The invention relates to the technical field of crystal growth, in particular to a double-crucible real-time feeding growth method for niobium potassium tantalate crystals. According to the technology, the dynamic relation between the raw material ratio and the crystal weight is effectively established by accurately regulating and controlling the supply rate of the raw materials, and the ratio of the replenishment material is flexibly adjusted according to the growth condition and the actual demand of the crystal by adopting the double-crucible real-time feeding technology. On the basis, technological parameters of crystal growth are further scientifically and reasonably optimized and designed, so that stable and repeatable growth of the large-size and high-optical-quality KTN crystal is successfully realized.

Description

Technical Field

[0001] The invention relates to the technical field of crystal growth, and in particular to a double-crucible real-time material addition growth method for potassium niobium tantalate crystals. Background Art

[0002] The secondary electro-optic effect, also known as the Kerr effect, refers to the effect that under the action of an external electric field, an isotropic material will exhibit birefringence, resulting in a change in the refractive index, and the change in the refractive index is proportional to the square of the electric field strength. Commonly used secondary electro-optic crystals mainly include cubic crystals such as potassium niobium tantalate (KTN), lithium tantalate (LiTaO3), and barium titanate (BaTiO3). These crystals have isotropic optical properties when no electric field is applied, and the refractive index ellipsoid is a rotating spherical surface. When an external electric field is applied, the refractive index ellipsoid will change, resulting in a secondary electro-optic effect.

[0003] KTN crystal is the crystal with the largest secondary electro-optic coefficient known so far. The secondary electro-optic effect of KTN crystal is remarkable and can be used to change the phase, intensity and propagation direction of light. It has broad application prospects in the fields of optical communication, screen display and biomedicine. Laser modulation components such as optical switches, optical holographic storage, optical deflectors, Q switches, etc. based on KTN crystals are gradually entering the laser product market.

[0004] The growth of KTN crystals is mainly carried out by the Czochralski method. During the growth of KTN crystals, high-quality, large-sized KTN single crystals can be obtained by precisely controlling the growth process parameters, such as temperature, solution concentration, pulling speed, and rotation speed. Due to the infinite solid solution characteristics of KTN crystals, there is a large difference between the crystal and melt composition during the crystal growth process. Existing crystal growth methods, such as the Czochralski method and the molten salt method, will inevitably lead to temperature fluctuations and changes in the melt composition during the crystal growth process. These changes will further affect the composition of the crystal, thereby causing abnormal crystal growth, such as the formation of growth stripes, hollow cores, etc., which will reduce the optical quality of the crystal. Especially when trying to grow large-sized KTN crystals, it is difficult to ensure the size and uniformity of the crystal at the same time. Summary of the invention

[0005] In order to solve the problem of uneven composition of KTN crystals caused by the segregation effect during the Czochralski growth process, we introduced the double-crucible real-time feeding technology, which effectively established a dynamic connection between the raw material ratio and the crystal weight by accurately controlling the supply rate of the raw materials. On this basis, we further optimized the process parameters of crystal growth in a scientific and reasonable manner, thereby successfully achieving the stable and repeatable growth of large-size, high-optical-quality KTN crystals.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A double crucible real-time feeding growth method for potassium tantalate niobate crystal comprises the following steps:

[0008] (1) Place the base material in a crucible and load the supplementary material into a feeder;

[0009] (2) heating at a heating rate of 90-110° C. per hour until the base material in the crucible is completely melted;

[0010] (3) Continue heating to 1100-1300°C, keep constant temperature overheating for 2-4 hours, and the heating rate is 40-60°C / h;

[0011] (4) Cooling the melt to the melting point at a rate of 40-60°C per hour, and starting seeding and necking;

[0012] (5) When the seed crystal shrinks to less than Φ1 mm, the feeder is turned on by the automatic feeding system, the automatic feeding program is started, and the feeding material is added according to the weight change of the crystal;

[0013] (6) Cool down to 5-15°C below the melting point at a rate of 8-12°C per hour and begin to release the shoulder;

[0014] (7) After the shoulder is released, the temperature is raised to 1100-1200°C at a rate of 3-6°C per hour to enter the neck growth stage;

[0015] (8) When the crystal rod grows to the required length, turn off the feeder and feeding program, and lift the crystal off the liquid surface;

[0016] (9) After the crystal is taken out, the system is kept at a constant temperature for 3-5 hours, then cooled to room temperature at a rate of 40-60° C. per hour, and the crystal is taken out;

[0017] The base material is prepared by using K2CO3, Ta2O5 and Nb2O5 as raw materials, and the raw materials are weighed and mixed according to a molar ratio of 1.2:0.3:0.7;

[0018] The preparation of the feed material uses K2CO3, Ta2O5 and Nb2O5 as raw materials, and the relationship between the crystal weight mass and the raw material molar ratio of the added feed material is:

[0019] When the crystal weight is 0-30g, no addition is required; when the crystal weight is 30-50g, K2CO3:Ta2O5:

[0020] Nb2O5=1.2:0.25:0.75; when the crystal weight is 50-100g, K2CO3:Ta2O5:Nb2O5=1.2:0.32:0.68;

[0021] When the crystal weight is 100-150g, K2CO3:Ta2O5:Nb2O5=1.2:0.41:0.59; when the crystal weight is greater than or equal to 150g, K2CO3:Ta2O5:Nb2O5=1.2:0.5:0.5;

[0022] The relationship between the amount of feed and crystal weight is: when the crystal weight is 0-30g, the amount of feed is 0g; when the crystal weight is 30-50g, the amount of feed is 30g; when the crystal weight is 50-100g, the amount of feed is 45g; when the crystal weight is 100-150g, the amount of feed is 65g;

[0023] When the crystal weight is 150-200g, the amount of supplementary material is 60g; when the crystal weight is 200-250g, the amount of supplementary material is 50g; when the crystal weight is greater than or equal to 250g, the amount of supplementary material is 50g for every 50g increase in crystal weight. In principle, the supplementary material should be added when the initial value is reached. For example, when the crystal weight is 30g, 30g of supplementary material should be added at a time.

[0024] A further improvement of this scheme is that the preparation method of the base material is as follows: KTN with a Curie point near room temperature is selected as the target crystal for growth, and the base material raw materials K2CO3, Ta2O5 and Nb2O5 are weighed and mixed according to a molar ratio of 1.2:0.3:0.7, and then pressed into blocks under a pressure of 15 Pa, and then sintered at a high temperature of 1020°C for 48 hours to obtain the required base material.

[0025] A further improvement of the present scheme is that the feed material is prepared as follows: the feed material raw materials K2CO3, Ta2O5 and Nb2O5 are mixed evenly, pressed into shape, sintered at 1050°C for more than 24 hours, ground into powder after cooling, pressed again and sintered for a second time for 48 hours, and finally ground and pressed into pills as a feed material for KTN crystals.

[0026] With further improvement of this scheme, the purity of K2CO3, Ta2O5 and Nb2O5 reaches 99.99%.

[0027] A further improvement of the present scheme is that in step 2, after melting, the liquid surface of the melt is kept at a distance of 9-11 mm from the upper edges of the inner and outer crucible walls, and the melting point temperature is 1050-1200°C.

[0028] A further improvement of the present solution is that during the necking process in step 4, the pulling speed of the seed crystal rod is 0.50.5±0.1 mm / h, and the crystal rotation speed is 8-12 revolutions per minute.

[0029] A further improvement of the present scheme is that during the shoulder release process in step 6, the pulling speed is reduced to 0.3±0.1 mm / h.

[0030] A further improvement of the present scheme is that the pulling speed in the neck growth stage of step 7 is 0.5±0.1 mm / h.

[0031] A further improvement of this solution is that the automatic feeding system consists of a weighing system, a computer control system, a feeding bin, a feeding pipe and an electric device. The computer control system reads the data of the weighing system and controls the electric device to open different feeding bins according to a preset program to achieve real-time feeding. The feeding bin is placed at an angle of 65° to the vertical direction and adopts a grid design.

[0032] Further improvements to this solution include the following steps:

[0033] (1) Place the base material in a platinum crucible and load the supplementary material into a feeder;

[0034] (2) heating at a rate of 100° C. per hour until the base material is completely melted, maintaining a distance of 10 mm between the melt surface and the upper edge of the inner and outer crucible walls, and a melting point temperature of 1050° C.;

[0035] (3) Continue heating to 1200°C and keep constant temperature for 4 hours at a heating rate of 50 / h;

[0036] (4) Cooling the melt to the melting point at a rate of 50° C. per hour, starting seeding and necking. During the necking process, the pulling speed of the seed crystal rod is 0.5 mm / h and the crystal rotation speed is 10 revolutions per minute;

[0037] (5) When the seed crystal shrinks to less than Φ1 mm, turn on the feeder, start the automatic feeding program, and add supplementary material in a timely and appropriate amount according to the weight change of the crystal;

[0038] (6) Cool down the temperature to 10°C below the melting point at a rate of 10°C per hour and start shoulder release. During the shoulder release process, the pulling speed is reduced to 0.3 mm / h;

[0039] (7) After the shoulder is released, the temperature is raised to 1145°C at a rate of 5°C per hour, and the pulling speed is increased to 0.5 mm / h to enter the equal neck growth stage;

[0040] (8) When the crystal rod grows to the required length, turn off the feeder and feeding program, and quickly lift the crystal 15 mm above the liquid surface;

[0041] (9) After the crystals were taken out, the system was kept at a constant temperature for 4 hours, then cooled to room temperature at a rate of 50°C per hour, and the crystals were taken out.

[0042] Compared with the prior art, the advantages and positive effects of the present invention are:

[0043] (1) To address the problem of component non-uniformity caused by the segregation effect during the growth of KTN crystals by the Czochralski method, the double-crucible real-time feeding technology was innovatively introduced. This technology cleverly constructed a dynamic balance between the raw material ratio and the crystal weight through a high-precision raw material supply rate control mechanism, significantly improving the uniformity of component distribution.

[0044] (2) The present invention selects and regulates the components of the feed material according to the growth characteristics of the KTN crystal, and can obtain crystals with a Ta / Nb ratio close to the theoretical ratio.

[0045] (3) On this basis, we further conducted in-depth scientific analysis and rational optimization of the entire process parameter system for crystal growth, and ultimately achieved stable and repeatable growth of large-sized KTN crystals, and these crystals exhibited excellent optical quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the feed bin structure;

[0047] Figure 2 This is a uniformity test of the KTN crystal grown in Example 4. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0049] The double crucible consists of an inner crucible and an outer crucible. The inner crucible is a cylinder without a bottom and is provided with a hanging hook, and the outer crucible is a solid-bottom cylinder. The inner and outer crucibles are placed concentrically, have the same upper ends, and are connected at the bottom. The base material is placed in the inner crucible, and the feed material is placed in the outer crucible.

[0050] Example 1: Preparation of KTN crystal growth base material

[0051] High-purity KCO3 (99.99%), Ta2O5 (99.99%) and Nb2O5 (99.99%) were selected as raw materials. The raw materials were accurately weighed and mixed according to the molar ratio of 1.2:0.3:0.7, and then pressed into blocks under a pressure of 15 Pa, and then sintered at a high temperature of 1020°C for 48 hours to obtain the base material.

[0052] Example 2: Preparation of KTN crystal growth feed

[0053] The raw materials of KCO3 (99.99%), Ta2O5 (99.99%) and Nb2O5 (99.99%) were weighed again, and the molar ratios were calculated as shown in Table 1. Then, they were mixed evenly and pressed into a mold. Next, they were sintered at 1050°C for 24 hours, and ground into powder after cooling. The powder was pressed again and sintered for a second time at the same temperature for 48 hours. Finally, the sintered material was ground and pressed into a pill shape, which was used as a supplement for KTN crystals.

[0054] For the relationship between the Ta / Nb molar ratio (K molar ratio is fixed at 1.2) and the crystal weight in the feed, see Table 1 below.

[0055] Crystal weight (g) Ta / Nb 0-30 No Addition 30-50 0.25：0.75 50-100 0.32:0.68 100-150 0.41:0.59 150-250 0.50:0.5 ≥250 0.50:0.5

[0056] Table 1 Relationship between Ta / Nb and crystal weight in feed For the relationship between feed amount and crystal weight, see Table 2 below.

[0057] Crystal weight (g) Feeding amount (g) 0-30 0 30-50 30 50-100 45 100-150 65 150-200 60 200-250 50 ≥250 For every 50g increase in crystal weight, add 50g of feed

[0058] Table 2 Relationship between feed amount and crystal weight

[0059] Example 3: Design of automatic feeding system

[0060] The automatic feeding system consists of a weighing system, a computer control system, a feeding bin, a feeding pipe and an electric device. The computer control system is responsible for reading the data of the weighing system and controlling the electric device to open different feeding bins according to the preset program to achieve real-time feeding.

[0061] During the charging process of crystal growth, it is necessary to add the corresponding feed materials to each silo in the feed silo in advance. At the beginning of crystal growth, the feed silo is closed. As the crystal is lifted, the weighing system will feed back the weight of the crystal to the computer. Based on this feedback, the system controls the corresponding electric device to open the feed silo, and the powder enters the crucible along the feeding pipe. This design not only improves the efficiency and stability of crystal growth, but also significantly reduces manual intervention, reducing the difficulty and cost of operation.

[0062] The entire feeding bin is placed at an angle of 65° to the vertical direction. The bin adopts a grid design, such as Figure 1 shown.

[0063] Example 4: Growth and preparation of KTN crystal

[0064] During the crystal growth process, we need to flexibly adjust the feed ratio according to the crystal growth status and actual needs. The specific operation steps are as follows: First, read the current crystal weight data and analyze the change in crystal mass; then, based on these analysis results, select the appropriate crystal growth feed ratio. The feed is added in stages, that is, according to the growth stage and weight of the crystal, it is added in a timely and appropriate amount to ensure the continuity and stability of crystal growth.

[0065] Next, the base material prepared in Example 1 is placed in a platinum crucible, and the supplementary material of Example 2 is loaded into the feeder. Subsequently, heating is performed at a heating rate of 100°C per hour until the base material is completely melted. At this time, the melt surface needs to be kept 10 mm away from the upper edge of the inner and outer crucible walls, and the melting point temperature is about 1050°C. The temperature is continued to be raised to 1200°C, and constant temperature overheating is performed at this temperature for 4 hours, and the heating rate is 50°C / h.

[0066] After that, the melt is cooled to the melting point at a rate of 50°C per hour, and seeding and necking begin. During the necking process, the pulling speed of the seed crystal rod is 0.5mm / h, and the crystal rotation speed is 10 revolutions per minute. When the seed crystal shrinks to less than Φ1mm, the upper scale is reset to zero, and the feeder is turned on to start the automatic feeding program. According to the weight change of the crystal, the feed is added in a timely and appropriate amount. Subsequently, the temperature is lowered to 10°C below the melting point at a cooling rate of 10°C per hour, and the shoulder is released. During the shoulder release process, the pulling speed is reduced to 0.3mm / h.

[0067] After the shoulder is released, the temperature is raised to 1145°C at a rate of 5°C per hour, and the pulling speed is increased to 0.5mm / h to enter the equal neck growth stage. During the equal neck growth process, the temperature should be kept constant as much as possible. When the crystal rod grows to the required length, turn off the feeder and the feeding program. Then, quickly lift the crystal 15mm away from the liquid surface. After the crystal is taken out, the system needs to be kept at a constant temperature for 4 hours, and then cooled to room temperature at a rate of 50°C per hour. Finally, take out the crystal and the growth process is over. The relationship between Ta / Nb and crystal weight in the feed is shown in Table 1, and the relationship between the feed amount and the crystal weight is shown in Table 2.

[0068] Example 5: Growth and preparation of KTN crystal

[0069] The base material prepared in Example 1 is placed in a platinum crucible, and the supplementary material of Example 2 is loaded into the feeder. Subsequently, heating is performed at a heating rate of 90°C per hour until the base material is completely melted. At this time, the melt surface must be kept 9 mm away from the upper edge of the inner and outer crucible walls, and the melting point temperature is 1050°C. The temperature is continued to rise to 1100°C, and constant temperature overheating is performed at this temperature for 2 hours, and the heating rate is 40°C / h.

[0070] After that, the melt is cooled to the melting point at a rate of 40°C per hour, and seeding and necking begin. During the necking process, the pulling speed of the seed crystal rod is 0.4mm / h, and the crystal rotation speed is 8 revolutions per minute. When the seed crystal shrinks to less than Φ1mm, the upper scale is reset to zero, and the feeder is turned on to start the automatic feeding program. According to the weight change of the crystal, the feed is added in a timely and appropriate amount. Subsequently, the temperature is lowered to 5°C below the melting point at a cooling rate of 8°C per hour, and the shoulder is released. During the shoulder release process, the pulling speed is reduced to 0.2mm / h.

[0071] After the shoulder is released, the temperature is raised to 1100°C at a rate of 3°C per hour, and the pulling speed is increased to 0.4mm / h to enter the neck growth stage. During the neck growth process, the temperature should be kept constant as much as possible. When the crystal rod grows to the required length, turn off the feeder and the feeding program. Then, quickly lift the crystal 10mm away from the liquid surface. After the crystal is taken out, the system needs to be kept at a constant temperature for 3 hours, and then cooled to room temperature at a rate of 40°C per hour. Finally, take out the crystal and the growth process ends. The relationship between Ta / Nb and crystal weight in the feed is shown in Table 1, and the relationship between the feed amount and the crystal weight is shown in Table 2.

[0072] Example 6: Growth and preparation of KTN crystal

[0073] The base material prepared in Example 1 is placed in a platinum crucible, and the supplementary material of Example 2 is loaded into the feeder. Subsequently, the base material is heated at a heating rate of 110°C per hour until the base material is completely melted. At this time, the melt surface needs to be kept 11 mm away from the upper edge of the inner and outer crucible walls, and the melting point temperature is 1050°C. The temperature is continued to rise to 1300°C, and the temperature is kept constant at this temperature for 4 hours, and the heating rate is 60°C / h.

[0074] After that, the melt is cooled to the melting point at a rate of 60°C per hour, and seeding and necking begin. During the necking process, the pulling speed of the seed crystal rod is 0.6mm / h, and the crystal rotation speed is 12 revolutions per minute. When the seed crystal shrinks to below Φ1mm, the upper scale is reset to zero, and the feeder is turned on to start the automatic feeding program. According to the weight change of the crystal, the feed is added in a timely and appropriate amount. Subsequently, the temperature is lowered to 15°C below the melting point at a cooling rate of 12°C per hour, and the shoulder is released. During the shoulder release process, the pulling speed is reduced to 0.4mm / h.

[0075] After the shoulder is released, the temperature is raised to 1200°C at a rate of 6°C per hour, and the pulling speed is increased to 0.6mm / h to enter the neck growth stage. During the neck growth process, the temperature should be kept constant as much as possible. When the crystal rod grows to the required length, turn off the feeder and the feeding program. Then, quickly lift the crystal 15mm away from the liquid surface. After the crystal is taken out, the system needs to be kept at a constant temperature for 5 hours, and then cooled to room temperature at a rate of 60°C per hour. Finally, take out the crystal and the growth process ends. The relationship between Ta / Nb and crystal weight in the feed is shown in Table 1, and the relationship between the feed amount and the crystal weight is shown in Table 2.

[0076] Example 7 Crystal composition uniformity test

[0077] Examples 4, 5, and 6 all obtained crystals with high appearance quality. To detect the uniformity of the composition of the prepared KTN crystals, we used the electron probe method to test the uniformity of the composition of the sample in Example 4. By sampling along the axial and radial directions of the crystal, the composition distribution of the crystal within a range of 1 cm in the (100) and (001) directions was detected. The results showed that the composition fluctuation along the growth direction was within 5 / cm, indicating that the crystal had good uniformity.

[0078] Therefore, in response to the current difficulties faced in the growth process of KTN crystals, the present invention proposes a pulling growth method using double crucible feeding. Compared with other existing double-crucible feeding methods for crystals, the present invention innovatively establishes a dynamic relationship between the feed and the weight of the crystal, thereby more effectively ensuring the consistency of the crystal composition with the target composition. In addition, by optimizing the crystal growth process, the present invention achieves the stable growth of large-size, high-optical-quality KTN crystals, which effectively promotes the industrialization process of KTN crystals. This achievement not only solves the long-standing problem of uneven components, but also lays a solid foundation for the industrial production of high-performance KTN crystals.

Claims

1. A double crucible real-time feeding growth method for potassium tantalate niobate crystal, characterized in that: The following steps are involved: (1) Place the base material in a crucible and load the supplementary material into a feeder; (2) heating at a heating rate of 90-110° C. per hour until the base material in the crucible is completely melted; (3) Continue heating to 1100-1300°C, keep constant temperature overheating for 2-4 hours, and the heating rate is 40-60°C / h; (4) Cooling the melt to the melting point at a rate of 40-60°C per hour, and starting seeding and necking; (5) When the seed crystal shrinks to less than Φ1 mm, the feeder is turned on by the automatic feeding system, the automatic feeding program is started, and the feeding material is added according to the weight change of the crystal; (6) Cool down to 5-15°C below the melting point at a rate of 8-12°C per hour and begin to release the shoulder; (7) After the shoulder is released, the temperature is raised to 1100-1200°C at a rate of 3-6°C per hour to enter the neck growth stage; (8) When the crystal rod grows to the required length, turn off the feeder and feeding program, and lift the crystal off the liquid surface; (9) After the crystal is taken out, the system is kept at a constant temperature for 3-5 hours, then cooled to room temperature at a rate of 40-60° C. per hour, and the crystal is taken out; The base material is prepared by using K2CO3, Ta2O5 and Nb2O5 as raw materials, and the raw materials are weighed and mixed according to a molar ratio of 1.2:0.3:0.7; The preparation of the feed material uses K2CO3, Ta2O5 and Nb2O5 as raw materials, and the relationship between the crystal weight and the raw material molar ratio of the added feed material is: When the crystal weight is 0-30g, no addition is required; when the crystal weight is 30-50g, K2CO3:Ta2O5: Nb2O5=1.2:0.25:0.75; when the crystal weight is 50-100g, K2CO3:Ta2O5:Nb2O5=1.2:0.32:0.68; When the crystal weight is 100-150g, K2CO3:Ta2O5:Nb2O5=1.2:0.41:0.59; when the crystal weight is greater than or equal to 150g, K2CO3:Ta2O5:Nb2O5=1.2:0.5:0.5; The relationship between the amount of feed supplement and the crystal weight is: when the crystal weight is 0-30g, the amount of feed supplement is 0g; when the crystal weight is 30-50g, the amount of feed supplement is 30g; when the crystal weight is 50-100g, the amount of feed supplement is 45g; when the crystal weight is 100-150g, the amount of feed supplement is 65g; when the crystal weight is 150-200g, the amount of feed supplement is 60g; when the crystal weight is 200-250g, the amount of feed supplement is 50g; when the crystal weight is greater than or equal to 250g, the amount of feed supplement is 50g for every 50g increase in crystal weight.

2. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: The preparation method of the base material is as follows: KTN with a Curie point near room temperature is selected as the target crystal for growth, and the base material raw materials K2CO3, Ta2O5 and Nb2O5 are weighed and mixed according to a molar ratio of 1.2:0.3:0.7, and then pressed into blocks under a pressure of 15 Pa, and then sintered at a high temperature of 1020°C for 48 hours to obtain the required base material.

3. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: The feed material is prepared as follows: the feed raw materials K2CO3, Ta2O5 and Nb2O5 are mixed evenly, pressed into shape, sintered at 1050°C for 24 hours, ground into powder after cooling, pressed again and sintered for a second time for 48 hours, and finally ground and pressed into pills as the feed material for KTN crystals.

4. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 2 or 3, characterized in that: The purity of K2CO3, Ta2O5 and Nb2O5 reaches 99.99%.

5. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: In the step 2, after melting, the liquid surface of the melt is kept at a distance of 9-11 mm from the upper edges of the inner and outer crucible walls, and the melting point temperature is 1050-1200°C.

6. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: During the necking process in step 4, the pulling speed of the seed crystal rod is 0.5±0.1 mm / h, and the crystal rotation speed is 8-12 revolutions per minute.

7. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: During the shoulder release process in step 6, the pulling speed is reduced to 0.3±0.1 mm / h.

8. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: The pulling speed in the neck growth stage of step 7 is 0.5±0.1 mm / h.

9. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: The automatic feeding system consists of a weighing system, a computer control system, a feeding bin, a feeding pipe and an electric device. The computer control system reads the data from the weighing system and controls the electric device to open different feeding bins according to the preset program to achieve real-time feeding. The feeding bin is placed at an angle of 65° to the vertical direction and adopts a grid design.

10. The double crucible real-time feeding growth method of potassium tantalate niobate crystal according to claim 1, characterized in that: The following steps are involved: (1) Place the base material in a platinum crucible and load the supplementary material into a feeder; (2) heating at a heating rate of 100° C. per hour until the base material is completely melted, maintaining a distance of 10 mm between the melt surface and the upper edge of the inner and outer crucible walls, and the melting point temperature is 1050° C.; (3) Continue heating to 1200°C and keep constant temperature for 4 hours at a heating rate of 50 / h; (4) Cooling the melt to the melting point at a rate of 50° C. per hour, starting seeding and necking. During the necking process, the pulling speed of the seed crystal rod is 0.5 mm / h and the crystal rotation speed is 10 revolutions per minute; (5) When the seed crystal shrinks to less than Φ1 mm, turn on the feeder, start the automatic feeding program, and add supplementary material in a timely and appropriate amount according to the weight change of the crystal; (6) Cool down the temperature to 10°C below the melting point at a rate of 10°C per hour and start shoulder release. During the shoulder release process, the pulling speed is reduced to 0.3 mm / h; (7) After the shoulder is released, the temperature is raised to 1145°C at a rate of 5°C per hour, and the pulling speed is increased to 0.5 mm / h to enter the equal neck growth stage; (8) When the crystal rod grows to the required length, turn off the feeder and feeding program, and quickly lift the crystal 15 mm above the liquid surface; (9) After the crystals were taken out, the system was kept at a constant temperature for 4 hours, then cooled to room temperature at a rate of 50°C per hour, and the crystals were taken out.

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