A method for producing a ktn single crystal

Abstract

The present application relates to a kind of preparation methods of KTN single crystal.The present application utilizes the eccentric growth technology and optimized related process parameters, can reduce the hollow rate to below 10%, greatly improve the utilization rate of crystal, further promote the commercial application of KTN crystal.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of functional crystal material preparation, and particularly relates to a preparation method of potassium tantalum niobate crystal. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing an understanding of the general background of the application and does not necessarily constitute an admission by the patent applicant or the like that the information forms part of the prior art that is already known in this field.

[0003] Potassium tantalum niobate crystal (KTN) is currently known as a crystal with the largest quadratic electro-optic effect, and its quadratic electro-optic coefficient can reach 10 -14 m 2 / V 2 orders of magnitude. Compared with LN crystal, the electro-optic effect of KTN crystal is more than 70 times that of LN crystal, so the optical device based on the quadratic electro-optic effect of KTN crystal has more advantages in reducing the driving voltage and reducing the size of the device, and can better meet the needs of the future miniaturization and integration of electro-optic devices.

[0004] Although KTN crystal has excellent quadratic electro-optic performance and photorefractive performance, it is difficult to obtain a large-size KTN crystal with uniform optical properties due to the segregation effect and volatilization of raw materials under high temperature conditions. Since the 1960s, many KTN crystal growth methods have been proposed, such as molten salt method, float crystal method, hydrothermal method, crucible lowering method, top seed pulling method, etc. However, it is difficult to grow KTN crystals with large size and high quality, especially the "hollow core" phenomenon exists in the growth process of large-size crystals (the length of the crystal is higher than 5 cm, and the hollow core rate is as high as 60%), which increases the difficulty of crystal processing and greatly reduces the utilization rate of the crystal. Therefore, it is urgent to explore a method for large-scale growth of high-quality and large-size KTN crystals. SUMMARY

[0005] To solve the above technical problems, the application provides a top seed crystal method for growing KTN crystals, which can reduce the hollow core rate to below 10% by using the off-core growth technology and optimized related process parameters, greatly improving the utilization rate of the crystal and further promoting the commercial application of KTN crystals.

[0006] To achieve the above technical purposes, the application provides the following technical solutions.

[0007] In a first aspect of the application, a seed crystal chuck is provided, which is composed of three parts: the upper part adopts a mortise and tenon structure to fix the corundum rod, the middle part is an off-core connecting seat, the off-core distance can be changed by changing the length of the connecting seat, and the lower part is a seed crystal chuck; the chuck is made of platinum material.

[0008] In the second aspect of the present application, a heating coil is provided, which adopts a variable-pitch design, with a total height of 165 mm, an inner diameter of 120 mm, a bottom pitch of 7 mm, a middle pitch of 5 mm, and a top pitch of 7 mm.

[0009] Further, the entire heating coil adopts a square copper tube with an outer diameter of 8 mm and a wall thickness of 1.5 mm, and circulating water is used inside the tube for heat dissipation of the coil itself.

[0010] In the third aspect of the present application, a KTN crystal growth device is provided, which comprises the seed crystal chuck, the heating coil, and the crucible.

[0011] In the fourth aspect of the present application, a method for preparing a KTN crystal using the KTN crystal growth device is provided, which comprises the following steps:

[0012] (1) Preparation of raw materials: the raw materials are K2CO3, Ta2O5, and Nb2O5, which are prepared according to a molar ratio of K:Ta:Nb of 1.08:0.3:0.7;

[0013] (2) After mixing the raw materials, ultrasonic dispersion is performed in a de-alcohol solution; after completion, stirring and ultrasonic dispersion are repeated for several times;

[0014] (3) After filtration, the dispersed raw materials are heated at a constant temperature for a period of time, ground, pressed into a block, and sintered at a high temperature to obtain a block-shaped polycrystalline material;

[0015] (4) Crystal growth is performed using the KTN crystal growth device.

[0016] Further, the purity of the raw materials used is 99.99%.

[0017] Further, in step (2), the ultrasonic frequency is 20 KHz, the power is set to 2000 W, and the ultrasonic time is 20 min.

[0018] Further, the number of repetitions is 2-5 times, preferably 3 times.

[0019] Further, the ratio of polycrystalline powder to alcohol solution is 100g:500ml, and the alcohol solution is prepared by mixing 95% alcohol and deionized water at a volume ratio of 1:1.

[0020] Further, in step (3), after filtration, the materials are transferred to a corundum crucible, slowly heated to 150℃, and kept at a constant temperature for 5 hours; pressed into a block at 108 Pa, and sintered at 900℃ for 12-15h.

[0021] Further, in step (4), the heating element is a platinum crucible, 2KHz intermediate frequency induction heating, the growth atmosphere is nitrogen, after loading, the temperature is raised to 1000-1100 DEG C, the temperature control precision is 0.2 DEG C; after the raw material is melted, the overheat is 1h, then the seed crystal is lowered into through the seed crystal clamp, through the process of seed lowering-necking-shoulder-constant neck growth, the KTN crystal is obtained.

[0022] Further, in step (4), the pulling speed during the growth process is 0.3-0.5mm / h; the crystal rotation speed is kept at 5r / min; after the growth is finished, the temperature is lowered to room temperature at 15-20 DEG C / h after the quick lifting from the liquid surface.

[0023] The method provided by the application can effectively reduce the 'empty core' rate, reduce the 'empty core' rate from 60% to 10%, increase the utilization rate of the crystal from the original 40% to 80%, further reduce the use cost of the KTN crystal, and promote the marketization process of the KTN crystal. BRIEF DESCRIPTION OF DRAWINGS

[0024] The drawings accompanying the specification of the application form a part of the application and serve to further provide a further understanding of the application, the illustrative embodiments of the application and the description thereof serve to explain the application without imposing undue limitations on the application.

[0025] Figure 1 is the design drawing of the eccentric seed crystal clamp.

[0026] Figure 2 is the intermediate frequency coil.

[0027] Figure 3 is the picture of the KTN crystal grown by the conventional (left) and eccentric method (right).

[0028] Figure 4 is the rocking curve of the KTN crystal grown by the eccentric method in example 2. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0030] Example 1 single crystal growth device

[0031] Seed crystal clamp design

[0032] As Figure 1As shown. To reduce the hollow phenomenon during KTN crystal growth, this invention specifically improves the seed crystal chuck. The chuck is made of platinum and consists of three parts: the upper part uses a tenon and mortise structure to fix the corundum rod, the middle part is an off-center connecting seat, the off-center distance can be changed by changing the length of the connecting seat, and the lower part is the seed crystal chuck (the edge part can also be made into a serrated shape for easy fixing of the seed crystal).

[0033] heating coil

[0034] like Figure 2 As shown. To construct a suitable temperature field for crystal growth, the coil used in this invention employs a variable-pitch design, which can achieve a temperature field with a high temperature in the middle and a low temperature at both ends. The coil has a total height of 165mm, an inner diameter of 120mm, a bottom spacing of 7mm, a middle spacing of 5mm, and a top spacing of 7mm; the entire coil is made of square copper tubing with an outer diameter of 8mm and a wall thickness of 1.5mm, and circulating water is circulated inside for heat dissipation.

[0035] Example 2: Off-center growth of cubic KTN crystals

[0036] 1) The raw materials used for growing KTN crystals are K2CO3, Ta2O5 and Nb2O5 with a purity of 99.99%. They are prepared according to the ratio of K:Ta:Nb ions of 1.08:0.3:0.7.

[0037] 2) Raw material pretreatment

[0038] The weighed polycrystalline powder was mixed in a mixer for 12 hours, then placed in deionized water and subjected to an ultrasonic disperser (SCIENTZ-3000F ultrasonic disperser). The ultrasonic frequency was set to 20 kHz, the power to 2000 W, and the ultrasonic time to 20 minutes. After completion, the mixture was stirred with a glass rod and ultrasonically dispersed again, repeating the process three times. The ratio of polycrystalline powder to alcohol solution was 100 g: 500 ml.

[0039] 3) Drying, grinding, and pressing polycrystalline materials into blocks

[0040] After the dispersed polycrystalline powder is filtered by an R300SS vacuum filter, it is transferred to an alumina crucible and slowly heated to 150°C and held at that temperature for 5 hours. After grinding again, it is pressed into blocks at 108 Pa and sintered at 900°C for 12-15 hours to obtain block polycrystalline material.

[0041] 4) Crystal growth

[0042] Crystal growth was performed in a single-crystal Czochralski furnace. The heating element was a platinum crucible, using 2kHz medium-frequency induction heating. The growth atmosphere was nitrogen. After loading the furnace, the temperature was raised to 1000–1100℃ with a temperature control accuracy of 0.2℃. After the raw material was melted and superheated for 1 hour, a seed crystal was added. Following a seeding-necking-shouldering-equal-necking growth process, a KTN crystal was obtained, as shown below. Figure 3(right). The pulling rate during growth was 0.3-0.5 mm / h; the crystal rotation rate was kept at 5 r / min; after the growth was finished, the crystal was quickly pulled away from the liquid surface and then cooled to room temperature at a rate of 15-20 °C / h. Figure 4 It can be seen that the grown KTN single crystal has good crystallization properties.

[0043] The size of the platinum crucible used in the experiment was Φ80 mm x 70 mm.

[0044] Example 3 Cu 2+ Off-center method for growing doped cubic phase KTN crystal

[0045] 1) The raw materials used for growing KTN crystal were CuO, K2CO3, Ta2O5 and Nb2O5 with a purity of 99.99%. The raw materials were prepared according to the K:Ta:Nb ion ratio of 1.08:0.3:0.7, and CuO was added according to 0.05% of the total mass of the raw materials.

[0046] 2) Raw material pretreatment

[0047] The weighed polycrystalline powder was mixed in a mixer for 12 hours, then put into deionized water and placed on an ultrasonic disperser (SCIENTZ-3000F ultrasonic disperser), with an ultrasonic frequency of 20 KHz and a power setting of 2000 W, and ultrasonic time of 20 min. After completion, the polycrystalline powder was stirred with a glass rod and then ultrasonically dispersed again, repeated for 3 times. The ratio of polycrystalline powder to alcohol solution was 100 g:500 ml.

[0048] 3) Drying, grinding and pressing of polycrystalline material

[0049] The dispersed polycrystalline powder was transferred to a corundum crucible after filtration by a R300SS vacuum filter, slowly heated to 150 °C and kept at this temperature for 5 hours, then ground again and pressed into a block under a pressure of 108 Pa, and sintered at 900 °C for 12-15 h to obtain a block of polycrystalline material.

[0050] 4) Furnace loading

[0051] Crystal growth was carried out. The heating element was a platinum crucible, heated by 2KHz intermediate frequency induction, and the growth atmosphere was nitrogen. After loading into the furnace, the temperature was raised to 1000-1100 °C, with a temperature control accuracy of 0.2 °C. After the raw material was melted and superheated for 1 h, the seed crystal was lowered, and the KTN crystal was obtained after the processes of seed lowering, necking, shoulder forming and constant neck growth. The pulling rate during growth was 0.3-0.5 mm / h; the crystal rotation rate was kept at 5 r / min; after the growth was finished, the crystal was quickly pulled away from the liquid surface and then cooled to room temperature at a rate of 15-20 °C / h.

[0052] The size of the platinum crucible used in the experiment was Φ80 mm x 70 mm.

[0053] Example 4 Growth of KTN crystal by conventional method

[0054] High purity (4N) K2CO3, Ta2O5 and Nb2O5 are weighed and mixed in a molar ratio of 1.25:0.34:0.66, and then pressed into a block. The block is placed in a platinum crucible and put into a muffle furnace to be sintered at 1050-1100°C for 24 hours to obtain KTN crystal polycrystal growth material. The sintered polycrystal material is re-ground, then pressed into a block, and placed in a platinum crucible and put into a single crystal growth furnace to grow crystals through the processes of seeding, diameter collection, shoulder placement, and equal-diameter growth, to obtain KTN crystals, as shown in Fig. (left). The pulling speed during equal-diameter growth is controlled at 0.5 mm / h, and the crystal rotation speed is 10-15 r / min. After growth, the temperature is decreased to room temperature at a rate of 10°C / h. Figure 3

[0055] Finally, it should be noted that the above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will still be able to modify the technical solutions described in the foregoing embodiments, or make equivalent replacements of some parts. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application. Although the specific embodiments of the present application have been described above, this is not intended to limit the protection scope of the present application. Those skilled in the art should understand that various modifications or changes made to the technical solutions of the present application without creative labor are still within the protection scope of the present application.​

Claims

1. A seed holder, characterized by, The seed clamp is composed of three parts: the upper part is fixed with the corundum rod by means of mortise and tenon structure, the middle part is a core offset connecting seat, the core offset distance can be changed by changing the length of the connecting seat, and the lower part is the seed clamp; the clamp is made of platinum material.

2. A KTN crystal growth apparatus, characterized by, The KTN crystal growth device comprises the seed clamp of claim 1, and a heating coil and a crucible. The heating coil adopts a variable distance design, the total height of the coil is 165 mm, the inner diameter is 120 mm, the bottom distance is 7 mm, the middle distance is 5 mm, and the top distance is 7 mm; the entire heating coil is made of a square copper pipe, the outer diameter of the pipe wall is 8 mm, the wall thickness is 1.5 mm, and circulating water is circulated in the inside for heat dissipation of the coil itself.

3. A KTN crystal growth method using the KTN crystal growth apparatus according to claim 2, characterized by, The method comprises the following steps: (1) batching: the raw materials are K2CO3, Ta2O5 and Nb2O5, and are prepared according to the molar ratio of K:Ta:Nb of 1.08:0.3:0.7; (2) after the raw materials are mixed, they are placed in an alcohol solution for ultrasonic dispersion; after completion, stirring and ultrasonic dispersion are repeated for several times; (3) after the dispersed raw materials are filtered, they are heated at a constant temperature for a period of time, ground, pressed into a block, and sintered at a high temperature to obtain a block-shaped polycrystalline material; (4) the KTN crystal growth device is used for crystal growth.

4. The method of claim 3, wherein, The purity of the raw materials used is 99.99%.

5. The method of claim 3, wherein, In step (2), the ultrasonic frequency is 20 KHz, the power is set to 2000 W, the ultrasonic time is 20 min, and the number of repetitions is 2-5 times.

6. The method of claim 5, wherein, In step (2), the number of repetitions is 3 times.

7. The method of claim 3 wherein, The ratio of the polycrystalline powder to the alcohol solution is 100g:500ml, and the alcohol solution is prepared by mixing 95% alcohol and deionized water at a volume ratio of 1:

1.

8. The method of claim 3, wherein, In step (3), after filtration, the materials are transferred to a corundum crucible, slowly heated to 150℃ and kept at this temperature for 5 hours; pressed into a block at 108Pa, and sintered at 900℃ for 12-15h.

9. The method of claim 3, wherein, In step (4), the heating element is a platinum crucible, 2KHz medium frequency induction heating, the growth atmosphere is nitrogen, after loading, the temperature is raised to 1000-1100℃, and the temperature control accuracy is 0.2℃; after the raw materials are melted, overheated for 1h, the seed crystal is lowered, and through the processes of seeding, necking, shoulder growth and equal neck growth, the KTN crystal is obtained.

10. The method of claim 3, wherein, In step (4), the pulling speed during the growth process is 0.3-0.5mm / h; the crystal rotation speed is kept at 5r / min; after the growth is completed, the temperature is lowered to room temperature at a rate of 15-20℃ / h after quickly lifting away from the liquid surface.

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