Rubidium potassium tantalate niobate double-solid-solution compound, nonlinear optical crystal and preparation method and application of nonlinear optical crystal

Abstract

The invention relates to a rubidium potassium tantalate niobate double-solid-solution compound, a nonlinear optical crystal and a preparation method and application of the nonlinear optical crystal. The chemical general formula of the compound is Rb < 1-x > K < x > Ta < 1-y > Nb < y > O < 3 > (0 lt; xlt; 1, 0lt; yt; Yt; the potassium rubidium tantalate niobate block single crystal has an ABO3 type perovskite structure, the crystal can be sequentially subjected to cubic-tetragonal-orthogonal-trigonal multi-time phase change from high temperature to low temperature, and the corresponding crystal point groups are m3m, 4mm, mm < 2 > and 3m respectively; the preparation method comprises the following steps: carrying out solid-phase reaction on rubidium carbonate, potassium carbonate, tantalum oxide and niobium oxide at a proper temperature, and carrying out a top seed crystal pulling method. The pure sample XRD diagram and the dielectric temperature spectrum of the obtained rubidium potassium tantalate niobate nonlinear optical crystal are matched with theoretical values, the relative dielectric constant and the secondary electro-optic coefficient are large, and the secondary electro-optic coefficient can reach 1.12 * 10 <-14 > m < 2 > / V2 near the room temperature.

Description

Technical Field

[0001] The invention relates to a potassium tantalate rubidium niobate double solid solution compound and a nonlinear optical crystal and a preparation method and application thereof, belonging to the field of nonlinear optical crystal materials. Background Art

[0002] ABO3 type ferroelectric single crystals with perovskite structure, such as BaTiO3, KTaO3, KNbO3, KTa 1-x Nb x O3, etc., is a type of displacement ferroelectric crystal with spontaneous polarization, and the direction of spontaneous polarization can change with the change of external electric field. This type of crystal can exist in both paraelectric phase and ferroelectric phase depending on the temperature and composition. It has many excellent properties such as piezoelectricity, ferroelectricity, electro-optics, photorefractive and nonlinear frequency conversion, and can be used in photoelectric detection, laser modulation, optical switch, laser ranging, information storage, optical communication and other fields.

[0003] In peroxide crystals with ABO3 perovskite structure, BO6 octahedrons are usually linked in a vertex-sharing manner, and A cations fill the octahedral gaps. When the B-site cation is at the center of the regular octahedron, the material is in a paraelectric phase, generally with a cubic phase m3m point group and a Pm3m space group; when the B-site cation deviates from the center position, the distribution of electronic states in the crystal is distorted, spontaneous polarization occurs, and the crystal becomes a ferroelectric phase, which can be a tetragonal phase 4mm or orthorhombic phase mm2 and other point groups. A prominent feature of the crystal material with this structure is that its A-site cations and B-site cations can be replaced by metal elements with similar properties to form a solid solution single crystal. Since different metal ions have different chemical properties such as ionic radius and valence state, the lattice structure of ABO3 solid solution single crystal can be optimized and controlled by adjusting the types and proportions of A-site and B-site cations, thereby adjusting the crystal's dielectric, piezoelectric, ferroelectric, electro-optical and other physical properties. This makes the physical properties of this type of crystals rich in adjustability and infinite possibilities, making it a hot topic of research and discussion in the field of modern functional crystal materials.

[0004] In the past, the method of adjusting the structure of ABO3 solid solution single crystal by adjusting the ion species and composition often only adjusts the A or B position. For example, the Li x K 1-x TaO3, KTa for B-site adjustment 1-x Nb x O3, etc., have not adjusted the A-site and B-site ions at the same time, and so far, there has been no report on potassium rubidium tantalate niobate compounds and potassium rubidium tantalate niobate nonlinear optical crystals. Summary of the invention

[0005] The object of the present invention is to simultaneously perform infinite solid solution on A-site and B-site ions on the basis of the traditional Czochralski method for preparing oxide crystals, and successfully synthesize a novel double solid solution compound of rubidium potassium tantalum niobate and a nonlinear optical crystal.

[0006] On the one hand, the present invention provides a double solid solution compound of rubidium potassium tantalum niobate. The chemical formula of this compound is Rb 1-x K x Ta 1- y Nb y O3 (hereinafter referred to as: RKTN; 0 ≤ x < 1, 0 < y < 1). At the same time, a bulk nonlinear optical single crystal of rubidium potassium tantalum niobate is provided, which has a perovskite structure of the ABO3 type. Among them, Rb and K elements occupy the A-site in the lattice and can be substituted for each other in any proportion, with a total stoichiometric ratio of 1; Ta element and Nb element occupy the B-site in the lattice and can also be substituted for each other in any proportion, with a total stoichiometric ratio of 1. This crystal will successively undergo multiple phase transitions from cubic to tetragonal to orthorhombic to trigonal from high temperature to low temperature, and the corresponding crystal point groups are m3m, 4mm, mm2, and 3m respectively.

[0007] On the second hand, a preparation method of the above-mentioned rubidium potassium tantalum niobate nonlinear optical crystal is provided. First, potassium carbonate, rubidium carbonate, tantalum oxide, and niobium oxide are synthesized by solid-phase reaction in air, and then a bulk single crystal is pulled out by the top-seeded Czochralski method in a Czochralski furnace. The XRD patterns and temperature-dependent dielectric permittivity spectra of the rubidium potassium tantalum niobate compound and the rubidium potassium tantalum niobate single crystal powder are in agreement with the theoretical values.

[0008] Specifically, the preparation steps of the double solid solution compound of rubidium potassium tantalum niobate and the rubidium potassium tantalum niobate nonlinear optical crystal are as follows:

[0009] (1) Using carbonates Rb2CO3, K2CO3 and oxides Nb2O5, Ta2O5 as raw materials, selecting an appropriate mixing ratio according to the required crystal composition, and obtaining a polycrystalline material of Rb 1-x K x Ta 1-y Nb y O3 through two sinterings;

[0010] (2) Growing crystals in a single crystal Czochralski furnace, melting the materials at 1150 - 1500 °C, growing crystals between 1200 - 1450 °C, and obtaining a crystal of Rb 1-x K x Ta 1-y Nb y O3 through the processes of seeding - necking - shoulder releasing - equal - diameter growth;

[0011] (3) After the crystal growth process is completed, cool down to room temperature at an appropriate cooling rate and take out the crystal.

[0012] This solution is further improved, and the preparation steps are as follows:

[0013] (1) Using high-purity Rb2CO3, K2CO3, Nb2O5, and Ta2O5 as raw materials, selecting ingredients according to the KT-KN solid solution phase diagram, weighing (Rb2CO3+K2CO3):(Nb2O5+Ta2O5) according to a molar ratio of (1.1-1.3):1, mixing them evenly and compacting them into blocks, pre-sintering them for the first time for 8-12 hours, taking them out and re-grinding them into powder, re-compacting them and pre-sintering them for a second time for 10-15 hours to obtain RKTN polycrystalline material;

[0014] (2) Crystal growth is carried out in a single crystal pulling furnace. The heating body is a platinum crucible, and the growth atmosphere is an atmospheric atmosphere. The blocky polycrystalline material is placed in the crucible, and after loading the furnace, the temperature is raised to 1150-1500°C to melt the raw material. After overheating for two hours, the seed crystal is placed in the crucible, and the RKTN single crystal is obtained through the process of seeding-neck shrinking-shoulder release-equal neck growth. Depending on the crystal composition, the crystal growth temperature is between 1200 and 1450°C. The pulling speed during the equal neck growth process is 0.25-0.5 mm / hour, the crystal rotation is 4-10 rpm, and the growth cycle is 5-10 days. After the crystal growth process is completed, the crystal is quickly lifted from the melt surface and kept at a constant temperature for 1-2 hours. For RKTN crystals with Curie points below room temperature (Tc≤25℃), the temperature can be cooled down to room temperature at a rate of 10-15℃ / h. For RKTN crystals with Tc>25℃, when the temperature is near the Curie point, the cooling rate needs to be adjusted to 1-2℃ / h to slowly cool to room temperature, and then the crystal can be taken out.

[0015] In the step 1, when 0≤x<0.35, the molar ratio of (Rb2CO3+K2CO3):(Nb2O5+Ta2O5) is preferably (1.1-1.15):1, the primary pre-sintering temperature is 750-825°C, and the secondary pre-sintering temperature is 850-900°C; when 0.35≤x<1, the molar ratio is preferably (1.2-1.3):1, the primary pre-sintering temperature is 850-930°C, and the secondary pre-sintering temperature is 950-975°C.

[0016] Further improvement of the present scheme, the preparation method of potassium rubidium tantalate niobate nonlinear optical crystal is as follows: weigh high-purity carbonate Rb2CO3, K2CO3 and high-purity metal oxide Ta2O5, Nb2O5 raw materials according to the molar ratio of Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.3:0.9:0.3:0.7, mix them, press them into blocks under a pressure of 30-50Mpa, put them into a platinum crucible, sinter them at 850°C for 8 hours, grind the polycrystalline material into powder again, mix them evenly, press them into blocks, repeat the previous sintering process, pre-sinter them at 975°C for 10 hours, and obtain RKTN polycrystalline material;

[0017] The RKTN polycrystalline material was placed in a platinum crucible and the crystal growth process was carried out in the atmosphere. When the temperature was raised to 1180°C, all the raw materials melted, and the temperature was continued to rise to about 1250 degrees, and the temperature was kept constant for 2 hours, and then the temperature was lowered to 1175 degrees, and the seed crystal was put in. After the necking, shouldering, and equal diameter growth process, a rectangular block crystal was obtained. During the crystal growth process, the crystal rotation was maintained at 5 rpm, the pulling speed was 0.3-0.5 mm / h, and the temperature of the equal diameter growth process was controlled between 1270-1280°C. After the crystal growth was completed, the crystal was taken out, kept rotating at 5 rpm, and cooled to room temperature at 15°C / h to obtain Rb 0.1 K 0.9 Ta 0.6 Nb 0.4 In addition, the present invention also provides the application of the above-mentioned double solid solution compound potassium rubidium tantalate niobate in the secondary electro-optical effect of a single crystal.

[0018] Further optimizing the sintering parameters according to the raw material components and controlling the grain growth can improve the performance of the material and increase its density and strength.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention uses a solid phase reaction method to synthesize a RKTN double solid solution compound for the first time, and uses a top seed crystal pulling method to grow a block RKTN single crystal for the first time. The crystal is a cubic column with an exposed crystal face of the

[100] face family, which brings convenience to the design and processing of the crystal. According to the characteristics of KTN crystals and the requirements of electro-optical crystal elements, we define the crystal growth direction as the z direction, and obtain processed samples with orientations of X squares, Z squares, (xyt)θ cut θ=15°, 30°, 45°, (xzt)θ cut (xyt)θ=15°, 30°, 45°, and x, b, z three-axis dimensions of 0 to 5 cm. At the same time, the invention achieves the simultaneous adjustment of the A and B positions by adjusting the ion species and components to adjust the ABO3 type solid solution single crystal structure, providing a reference for the modification of other materials.

[0021] (2) The RKTN crystal prepared by the present invention can exist in either a paraelectric phase or a ferroelectric phase according to the ratio of the four elements Rb:K:Ta:Nb in the components and the ambient temperature. Most of the RKTN crystals will undergo multiple phase transitions from high temperature to low temperature, from cubic to tetragonal to orthorhombic to trigonal, and the corresponding crystal point groups are m3m-4mm-mm2-3m. The multiple phase transitions of crystals from high temperature to low temperature provide rich possibilities for the performance optimization and multifunctional application of materials. By in-depth research and utilization of these phase transition characteristics, more efficient and intelligent material design and application may be achieved not only in the optoelectronic field, but also in electronics, thermal management, medical and other fields in the future.

[0022] (3) The potassium rubidium tantalate niobate nonlinear optical crystal of the present invention has a large relative dielectric constant and a secondary electro-optic coefficient. The secondary electro-optic coefficient can reach 1.12×10 -14 m 2 / V 2 , which can greatly expand the application of secondary electro-optical effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The RKTN native crystal and the RKTN optical element prepared in Example 1 of the present invention;

[0024] Figure 2 Schematic diagram of the RKTN single crystal unit cell structure of the present invention;

[0025] Figure 3 is a comparison chart of the X-ray powder diffraction spectrum of the RKTN single crystal powder of Example 7 of the present invention and the theoretical value;

[0026] Figure 4 The medium temperature spectrum of the RKNT crystal prepared in Example 8 of the present invention;

[0027] Figure 5 This is the power / voltage modulation curve of the RKTN optical element of Example 9 of the present invention under 633nm laser. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only 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 should fall within the scope of protection of the present invention.

[0029] Example 1: Rb 0.1 K 0.9 Ta 0.6 Nb 0.4 O3 compounds and single crystal preparation

[0030] High-purity carbonate Rb2CO3, K2CO3 and high-purity metal oxide Ta2O5, Nb2O5 raw materials are weighed according to the molar ratio of Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.3:0.9:0.3:0.7, mixed in a ball mill, pressed into blocks under a pressure of 30-50 MPa, placed in a platinum crucible, and initially sintered at 850°C in a muffle furnace for 8 hours. The raw materials undergo the following reaction: (Rb2CO3, K2CO3)+(Ta2O5, Nb2O5)=2(Rb, K)(Ta, Nb)O3+CO2↑, and about 1000 grams of KTN polycrystalline material is obtained. The polycrystalline material is re-ground into powder, mixed evenly, pressed into blocks, and the previous sintering process is repeated. A second pre-sintering at 975°C for 10 hours is performed to obtain RKTN polycrystalline material.

[0031] The RKTN polycrystalline material is placed in a platinum crucible and the crystal growth process is carried out in the atmosphere. The medium frequency heating method is used. When the temperature is raised to 1180 degrees, the raw material can be seen to be completely melted. The temperature is continued to rise to about 1250 degrees and kept constant for 2 hours. After that, the temperature is lowered to 1175 degrees, and the seed crystal is placed. After the necking, shouldering, and equal diameter growth process, a rectangular block of Rb is obtained. 0.1 K 0.9 Ta 0.6 Nb 0.4 O3. During the crystal growth process, the crystal rotation was maintained at 5 rpm, the pulling speed was 0.3-0.5 mm / h, the temperature during the equal diameter growth process was controlled between 1270-1280°C, and the growth cycle was 5 days. After the crystal growth was completed, the crystal was manually taken out, the crystal was 2 mm away from the liquid surface, and the rotation was maintained at 5 rpm, and the temperature was cooled to room temperature at 1°C / h to obtain the RKTN crystal sample ( Figure 1 ), the crystal is a cubic column, and the exposed crystal face is

[100] face family. According to the needs, the crystal is processed into 2.5mm×2.5mm×1mm wafers according to X square, Z square, (xyt)θ cut type θ=15°, 30°, 45° respectively ( Figure 1 ), used to measure the dielectric spectrum of the crystal ( Figure 4 ). Figure 2 Schematic diagram of the RKTN single crystal unit cell structure of the present invention.

[0032] Example 2: Rb 0.01 K 0.99 Ta 0.6 Nb 0.4 O3 compounds and single crystal preparation

[0033] The crystal growth preparation process of this embodiment is basically the same as that of Example 1, except that the raw material ratio is adjusted to Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.1:1.1:0.3:0.7, the total mass of the polycrystalline material is about 1000 grams, the initial pre-sintering temperature of the polycrystalline material is adjusted to 900°C, the secondary pre-sintering temperature is adjusted to 975°C, the seeding temperature during the crystal growth process is adjusted to about 1265°C, and the equal-diameter growth temperature is adjusted to 1260-1270°C.

[0034] Example 3: Rb 0.5 K 0.5 Ta 0.5 Nb 05 O3 compounds and single crystal preparation

[0035] The crystal growth preparation process of this embodiment is basically the same as that of Example 1, except that the raw material ratio is adjusted to Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.8:0.5:0.2:0.8, the total mass of the polycrystalline material is about 1000 grams, the initial pre-sintering temperature of the polycrystalline material is adjusted to 930°C, the secondary pre-sintering temperature is adjusted to 975°C, the seeding temperature during the crystal growth process is adjusted to about 1215°C, and the equal-diameter growth temperature is adjusted to 1215-1270°C.

[0036] Example 4: Rb 0.7 K 0.3 Ta 07 Nb 0.3 O3 compounds and single crystal preparation

[0037] The crystal growth preparation process of this embodiment is basically the same as that of Example 1, except that the raw material ratio is adjusted to Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.8:0.5:0.3:0.7, the total mass of the polycrystalline material is about 1000 grams, the initial pre-sintering temperature of the polycrystalline material is adjusted to 800°C, the secondary pre-sintering temperature is adjusted to 850°C, the seeding temperature during the crystal growth process is adjusted to about 1300°C, and the equal-diameter growth temperature is adjusted to 1300-1370°C.

[0038] Example 5: Rb 0.3 K 0.7 Ta 0.61 Nb 0.39 O3 compounds and single crystal preparation

[0039] The crystal growth preparation process of this embodiment is basically the same as that of Example 1, except that the raw material ratio is adjusted to Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.5:0.8:0.35:0.65, the total mass of the polycrystalline material is about 1000 grams, the initial pre-sintering temperature of the polycrystalline material is adjusted to 930°C, the secondary pre-sintering temperature is adjusted to 950°C, the seeding temperature during the crystal growth process is adjusted to about 1350°C, and the equal-diameter growth temperature is adjusted to 1350-1400°C.

[0040] Example 6: Rb 0.5 K 0.5 Ta 0.3 Nb 0.7 O3 compounds and single crystal preparation

[0041] The crystal growth preparation process of this embodiment is basically the same as that of Example 1, except that the raw material ratio is adjusted to Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.5:0.5:0.1:0.9, the total mass of the polycrystalline material is about 1000 grams, the initial pre-sintering temperature of the polycrystalline material is adjusted to 900°C, the secondary pre-sintering temperature is adjusted to 975°C, the seeding temperature during the crystal growth process is adjusted to about 1265°C, and the equal-diameter growth temperature is adjusted to 1265~1245°C.

[0042] Example 7: Rb 0.1 K 0.9 Ta 0.6 Nb 0.4 Analysis of O3 single crystal structure

[0043] In this embodiment, X-ray powder diffraction (XRD) is used to analyze the structure of the RKTN wafer grown in Example 1. After the crystal grown in Example 1 is cut, it is ground in an agate crucible for 15-30 minutes to a powder fineness of less than 3000 mesh (particle diameter 1-5um). The powder diffraction pattern of the RKTN crystal is measured at room temperature. The test results are as follows: Figure 3 As shown, it can be seen that the XRD patterns of the potassium rubidium tantalate niobate compound and the potassium rubidium tantalate niobate single crystal powder are consistent with the theoretical values ​​and have an ABO3 type perovskite structure.

[0044] Example 8: Rb 0.1 K 0.9 Ta 0.6 Nb 0.4 O3 single crystal phase analysis

[0045] This embodiment uses the LCR bridge method to measure the capacitance of the RKTN wafer grown in Example 1, calculates the relative dielectric constant based on the capacitance, and determines the crystal phase of the crystal at different temperatures based on the change of the dielectric constant with temperature (dielectric-temperature spectrum). The RKTN sample size is a×b×c=2.5mm×2.5mm×1mm, the electrode end surface is (010) surface, and the sample thickness is 1mm. Figure 4 The 10KHz dielectric spectrum of the RKTN crystal is consistent with the theoretical value. The results show that the RKTN crystal prepared in Example 1 meets the Curie-Weiss characteristics, the Curie phase transition temperature Tc = 33.9°C, and the crystal undergoes three phase transitions from high temperature to low temperature, namely m3m-4mm-mm2-3m, with phase transition temperatures of 33.9°C, -26.7°C, and -77.5°C respectively.

[0046] Example 9: Based on Rb 0.1 K 0.9 Ta 0.6 Nb 0.4 Laser Modulation of Secondary Electro-optic Effect of O3 Single Crystal

[0047] This example uses the sample processed in Example 8 to perform Rb 0.1 K 0.9 Ta 0.6 Nb 0.4 The laser modulation test of the secondary electro-optical effect of O3 single crystal uses a 633nm He-Ne laser. The light passes through the polarizer, RKTN crystal sample, analyzer and detector in sequence. An electric field is applied in the Y direction perpendicular to the crystal growth direction, and the light is passed parallel to the crystal growth direction. The light transmission length is 1mm. Finally, the detector receives the transmitted light intensity, measures the peak light intensity and then measures the half-wave voltage value. The results are as follows: Figure 5 , as shown, the final measured half-wave voltage V π =55.3V, the calculated secondary electro-optic coefficient of RKTN is 1.12×10 -14 m 2 / V 2 .

Claims

1. A dual solid solution compound of potassium rubidium tantalate niobate, characterized in that: The chemical formula of this compound is Rb 1-x K x Ta 1-y Nb y O3(0≤x<1,0 <y<1)。 2. A potassium rubidium tantalate niobate nonlinear optical crystal, characterized in that: The chemical formula is Rb 1-x K x Ta 1-y Nb y O3 (0 ≤ x < 1, 0 < y < 1), which is a bulk single crystal and has a perovskite structure of the ABO3 type; among them, the Rb and K elements occupy the A site in the lattice and can be substituted for each other in any proportion, with a total stoichiometric ratio of 1; the Ta element and the Nb element occupy the B site in the lattice and can be substituted for each other in any proportion, with a total stoichiometric ratio of 1.

3. The potassium rubidium tantalate niobate nonlinear optical crystal according to claim 2, characterized in that: The crystal will undergo multiple phase transitions from high temperature to low temperature, from cubic to tetragonal to orthorhombic to trigonal, and the corresponding crystal point groups are m3m, 4mm, mm2, and 3m respectively.

4. The method for preparing potassium rubidium tantalate niobate nonlinear optical crystal according to claim 2 or 3, characterized in that: The top seed crystal pulling method is used for growth, including the following steps: (1) Using carbonate Rb2CO3, K2CO3 and oxide Nb2O5, Ta2O5 as raw materials, selecting appropriate proportions according to the required crystal components, and sintering twice to obtain Rb 1-x K x Ta 1-y Nb y O3 polycrystalline material; (2) Grow crystals in a single crystal pulling furnace, melt at 1150-1500°C, grow crystals between 1200-1450°, and go through a process of seeding-neck-shoulder-equal neck growth to obtain Rb 1-x K x Ta 1-y Nb y O3 crystal; (3) After the crystal growth process is completed, cool to room temperature at an appropriate cooling rate and take out the crystal.

5. The method for preparing potassium rubidium tantalate niobate nonlinear optical crystal according to claim 4, characterized in that: In step (1), the molar ratio of the raw materials (Rb2CO3+K2CO3):(Nb2O5+Ta2O5) is (1.1-1.3):1; in step (2), the pulling speed of the crystal growth is 0.25-0.5 mm / hour, the crystal rotation speed is 4-10 rpm, and the growth period is 5-10 days.

6. The method for preparing potassium rubidium tantalate niobate nonlinear optical crystal according to claim 4, characterized in that: In step (3), for RKTN crystals with a Curie point Tc not greater than room temperature ≤ 25°C, the temperature is cooled to room temperature at a rate of 10 to 15°C / h; for RKTN crystals with Tc>25°C, when the temperature is cooled to near the Curie point, the cooling rate is adjusted to 1 to 2°C / h and slowly cooled to room temperature.

7. The method for preparing potassium rubidium tantalate niobate nonlinear optical crystal according to claim 5, characterized in that: When 0≤x<0.35, the molar ratio of (Rb2CO3+K2CO3):(Nb2O5+Ta2O5) is (1.1-1.15):1; when 0.35≤x<1, the molar ratio is (1.2-1.3):

1.

8. The method for preparing potassium rubidium tantalate niobate nonlinear optical crystal according to claim 4, characterized in that: In step (1), when 0≤x<0.35, the primary pre-sintering temperature is 750-825°C, and the secondary pre-sintering temperature is 850-900°C; when 0.35≤x<1, the primary pre-sintering temperature is 850-930°C, and the secondary pre-sintering temperature is 950-975°C; the primary pre-sintering is 8-12 hours, and the secondary pre-sintering is 10-15 hours.

9. The method for preparing potassium rubidium tantalate niobate nonlinear optical crystal according to claim 4, characterized in that: The steps include: The raw materials of high-purity carbonate Rb2CO3, K2CO3 and high-purity metal oxide Ta2O5, Nb2O5 are weighed according to the molar ratio of Rb2CO3:K2CO3:Ta2O5:Nb2O5=0.3:0.9:0.3:0.7, mixed, pressed into blocks under a pressure of 30-50Mpa, placed in a platinum crucible, and initially sintered at 850°C for 8 hours, the polycrystalline material is re-grinded into powder, mixed evenly, pressed into blocks, and the previous sintering process is repeated, and pre-sintered for a second time at 975°C for 10 hours to obtain RKTN polycrystalline material; The RKTN polycrystalline material was placed in a platinum crucible and the crystal growth process was carried out in an atmospheric atmosphere. When the temperature was raised to 1180 degrees, all the raw materials melted, and the temperature was continued to rise to about 1250 degrees, and the temperature was kept constant for 2 hours, and then the temperature was lowered to 1175 degrees, and the seed crystal was put in. After the necking, shouldering, and equal diameter growth process, a rectangular block crystal was obtained. During the crystal growth process, the crystal rotation was maintained at 5 rpm, the pulling speed was 0.3-0.5 mm / h, and the temperature of the equal diameter growth process was controlled between 1270-1280℃. After the crystal growth was completed, the crystal was taken out, kept rotating at 5 rpm, and cooled to room temperature at 1℃ / h to obtain Rb 0.1 K 0.9 Ta 0.6 Nb 0.4 O3 crystal.

10. Application of the potassium rubidium tantalate niobate nonlinear optical crystal according to claim 2 or 3 in the secondary electro-optical effect of a single crystal.

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