Preparation method of potassium-sodium niobate-based single crystal

Abstract

The invention discloses a preparation method of a potassium-sodium niobate-based single crystal, the chemical formula of the potassium-sodium niobate-based single crystal is # imgabs0 # x representing the mole fraction of Co element in a system, 0 < x < = 0.005, pre-seed crystals prepared by a seed-crystal-free solid-phase crystal growth method are subjected to surface growth residue and attachment removal, polishing, thinning and related treatment, and the potassium-sodium niobate-based single crystal is obtained. According to the method, the potassium-sodium niobate and the powder are pressed together to form a seed burying blank, the large-size potassium-sodium niobate-based single crystal grows through seed crystal induction, the advantages of a seed crystal-free solid phase method and a traditional solid phase method are combined, the stability of single crystal growth is ensured, and regulation and control of the growth orientation and size increase of the single crystal can be realized through accurate control of the seed crystal; the introduction of impurities can be avoided, and the repeatability and stability of single crystal growth are improved.

Description

Technical Field:

[0001] The present invention relates to the technical field of piezoelectric and ferroelectric single crystal preparation, and particularly relates to a method for preparing potassium sodium niobate-based single crystals. Background Art:

[0002] KNN (K 0.5 Na 0.5 NbO 3 )-based single crystals have broad application potential in fields such as sensors and actuators due to their excellent piezoelectric properties and environmental characteristics. Up to now, domestic and foreign scholars have carried out a large number of studies on the preparation methods of KNN-based single crystals and achieved certain progress. Among them, the main preparation methods include the Bridgeman method, the Czochralski method, and the Floating Zone method. The Bridgeman method is one of the classic methods for preparing KNN single crystals. As described in the literature [G. Xu, D. Yang, K. Chen, D. A. Payne, J. F. Carroll, J. Electroceram. 24, 226 - 230 (2009)], this method uses a temperature gradient to control the solidification process of the melt, thereby realizing the directional growth of crystals. However, due to the slow growth rate and the possible generation of large thermal stresses during the cooling process, it often limits the size and quality of the crystals, resulting in insufficient uniformity. The Czochralski method is a classic single crystal growth method, as detailed in the literature [L. Liu, F. Yin, G. Zhao, M. Zhu, Z. Jia, X. Fu, X. Tao, Crystal Growth & Design. 24, 774 - 780 (2023)]. Although this method can grow large-sized single crystals, impurities are often introduced during the melting process, thus affecting the purity and performance of the crystals. In addition, due to the large temperature gradient during the growth process, cracks and stress concentrations are likely to occur in the crystal, which not only reduces the structural integrity of the crystal but also has an adverse impact on the reliability of subsequent applications. Therefore, although the Czochralski method can meet the size requirements to a certain extent in the preparation of KNN single crystals, there is still much room for improvement in terms of quality and uniformity. The Floating Zone method is a technique capable of producing high-purity single crystals. As described in the literature [M. Bah, F. Giovannelli, R. Retoux, J. Bustillo, E. L. Clezio, I. Monot-Laffez, Crystal Growth & Design. 16, 315 - 324 (2016)], although this method can obtain a high crystal purity, it has high requirements for equipment accuracy and it is difficult to completely eliminate thermal stress during the growth process. These factors result in the method usually being able to produce only smaller-sized single crystals and having a slow growth rate.

[0003] The traditional solid-state method (SSCG) is a commonly used technique in the preparation of KNN single crystals, as described in the literature [Yang, J., Fu, Z., Yang, Q., Li, Y., & Liu, Y. Journal of the Ceramic Society of Japan, 124(4), 365 - 369 (2016)]. This method promotes crystal growth through high-temperature sintering and solid-state reactions, with a simple process and low equipment requirements. However, this method also has some deficiencies. First, the solid-state method relies on high-quality seed crystals for induction. The selected seed crystals are usually heterogeneous crystals with different compositions, such as KTaO 3 crystals, etc. They are not only expensive but also have a large difference in composition from KNN, inevitably introducing impurities and causing contamination. Second, due to the easy change of the crystal quality and orientation of the seed crystal, and the need to consider the lattice matching degree between the seed crystal and the embryo material, the crystal grows unevenly during the growth process, ultimately affecting the size and uniformity of the single crystal, which will affect the quality and performance of the crystal. In summary, although the traditional solid-state method is widely used in the preparation of KNN single crystals, there is still much room for improvement in avoiding impurity contamination, increasing the growth rate, crystal quality, uniformity, and performance, etc.

[0004] None of the above preparation methods have effectively solved the bottleneck problems of KNN-based single crystals in terms of impurity contamination introduction, growth rate, crystal quality, uniformity, and size control. Therefore, there is an urgent need to further improve the methods for growing KNN single crystals in terms of efficiency and quality.

[0005] In the previous work of the inventor's research group, Patent CN 106087058 A disclosed a kind of K 0.5 Na 0.5 NbO 3 -based ferroelectric and piezoelectric single crystal and its preparation method. By using the seedless solid-state method (SFSSCG), MnO 2 doping modification technology and annealing treatment technology, centimeter-scale xMnO 2 -(1–x)(99.6K 0.5 Na 0.5 NbO 3 -0.4LiBiO 3 )(0≤x≤0.005) ferroelectric and piezoelectric single crystals were successfully prepared. CN118127633A disclosed a potassium sodium niobate-based single crystal with stable piezoelectric properties in a wide temperature range and its preparation method, using Na 2 CO 3 、K 2 CO 3 、Nb 2 O 5 、Al 2 O3 , Bi 2 O 3 and Li 2 CO 3 Using Bi and LiCO as raw materials, by means of the seedless solid-phase crystal growth method, through primary refined ball milling, pre-sintering, secondary refined ball milling and sintering, a sodium potassium niobate-based single crystal doped with LiO can be prepared. CN106521627A discloses a sodium potassium niobate-based piezoelectric single crystal and its preparation method to improve the piezoelectric properties of the sodium potassium niobate-based single crystal. By doping an appropriate amount of CaZrO on the basis of the 99.6K NaNb - 0.4LiBiO-based single crystal, the purpose of significantly improving the piezoelectric properties of the sodium potassium niobate-based single crystal is achieved, but the above technology needs to be further improved. 2 On the basis of the 99.6K NaNb - 0.4LiBiO-based single crystal, by doping an appropriate amount of CaZrO, the piezoelectric properties of the sodium potassium niobate-based single crystal can be significantly improved, but the above technology needs to be further improved. 0.5 Na 0.5 NbO 3 -0.4LiBiO 3 On the basis of the single crystal, an appropriate amount of CaZrO is doped to achieve the purpose of significantly improving the piezoelectric properties of the sodium potassium niobate-based single crystal, but the above technology needs to be further improved. 3 , the above technology needs to be further improved. Summary of the Invention:

[0006] The object of the present invention is to provide a preparation method of a sodium potassium niobate-based single crystal, which solves the problems in the prior art that the growth rate of the KNN-based single crystal is slow, the growth rate is unstable, resulting in a small crystal size, easy introduction of impurity pollution, and low crystal quality and uniformity.

[0007] The present invention is achieved through the following technical solutions:

[0008] A preparation method of a sodium potassium niobate-based single crystal, the sodium potassium niobate-based single crystal has a size of more than 10mm×10mm×2mm, and the chemical formula is Using K 0.5 Na 0.5 NbO 3 as the main material, and using BaCO 3 , ZrO 2 , Co 3 O 4 , Li 2 CO 3 and Bi 2 O 3 as doping materials, where x represents the molar fraction of Co element in the system, where 0﹤x≤0.005, and preferably x is 0.005. Its preparation method includes the following steps:

[0009] 1) Preparation of pre-seed crystal: The pre-seed crystal is prepared by the seedless solid-phase crystal growth method, including primary refined ball milling, pre-sintering, secondary refined ball milling and sintering;

[0010] 2) Preparation of seed crystal: The pre-seed crystal grown in step 1) is peeled off from the round billet body, the surface growth residues and attachments are removed, and the qualified products are detected and screened. Then, it is polished along its exposed surface and growth surface, and the thickness is thinned to 0.5-1 mm and the size is regularized to obtain the seed crystal;

[0011] 3) Seed crystal-induced growth of sodium potassium niobate-based single crystal: The seed crystal obtained in step 2) is buried in the secondary ball-milled material prepared by secondary refinement ball milling in the process of preparing the pre-seed crystal by the seedless solid-phase crystal growth method described in step 1), pressed into a seed-embedded embryo under a pressure of 100-120 MPa, and finally sintered at 1100-1110 °C for 21-24 h to obtain a large-sized homogeneous sodium potassium niobate-based single crystal grown by seed crystal induction.

[0012] The preparation of the pre-seed crystal by the seedless solid-phase crystal growth method described in step 1) includes primary refinement ball milling, pre-sintering, secondary refinement ball milling and sintering; the specific steps are as follows:

[0013] (1) Primary refinement ball milling: Na 2 CO 3 , K 2 CO 3 , Nb 2 O 5 , Bi 2 O 3 , Li 2 CO 3 , BaCO 3 , ZrO 2 and Co 3 O 4 powder raw materials are dried at 120-140 °C for 12-18 h, and then accurately weighed according to the chemical formula and refined by ball milling. The ball milling tank is made of HDPE, the ball milling balls are made of zirconia, the ball milling medium is anhydrous ethanol, the ball milling time is 24-48 h, the ball milling speed is 380-450 r / min. After the ball milling is completed, the ball-milled material is dried and sieved. The drying temperature is 80-120 °C, the drying time is 8-12 h, and the sieving condition is to sieve with a 100-200 mesh sieve to finally obtain the raw material after primary refinement ball milling, which is called the primary ball-milled material;

[0014] (2) Pre-sintering treatment: The primary ball-milled material obtained in step (1) is pre-sintered at 650-800 °C for 6-8 h to obtain the pre-sintered material;

[0015] (3) Secondary Refinement Ball Milling: The pre-sintered material obtained in step (2) is subjected to secondary refinement ball milling. After the ball milling is completed, it is dried and sieved to obtain the raw material after secondary refinement ball milling, which is called the secondary ball milled material. The conditions for secondary refinement ball milling, drying conditions, and sieving conditions are the same as those in step (1) for primary refinement ball milling;

[0016] (4) Sintering: The secondary ball milled material is pressed into a round blank under a specific pressure of 100 - 120 MPa and held under pressure for 2 - 5 minutes. The diameter of the mold is 25 - 50 mm; Then, using the seedless solid-phase growth process, the round blank is sintered. The sintering temperature is 1100 - 1110 °C, and the sintering time is 21 - 24 h to obtain the potassium sodium niobate-based single crystal grown with this chemical formula ratio.

[0017] In step (2), the method for removing surface impurities is ultrasonic cleaning for 15 - 30 minutes, and when necessary, a cutting machine is used for cutting. Relevant detections include visual inspection, laser irradiation, XRD analysis, and SEM analysis.

[0018] The condition for embedding the seed crystal in step (3) is to place the seed crystal before pouring the secondary ball milled material into the mold, adjust the position, and then press them together into an embedded seed embryo.

[0019] The beneficial effects of the present invention are as follows: The growth of single crystals by the conventional seedless solid-phase method (SFSSCG) has great randomness and uncontrollability. The present invention uses the seedless solid-phase crystal growth method to prepare a pre-seed crystal, which becomes a standardized seed crystal after relevant detections and treatments, and is pressed together with the secondary ball milled material into an embedded seed embryo for inducing the growth of KNN-based single crystals. It combines the advantages of the seedless solid-phase method (SFSSCG) and the traditional solid-phase method (SSCG). It not only ensures the stability of single crystal growth but also can, through precise control of the seed crystal, achieve the regulation of the growth orientation of the single crystal, the increase in size, and the improvement of growth repeatability and controllability. Moreover, the crystal used as the seed crystal has the same chemical composition and will not introduce impurity pollution. This method effectively solves the problems in the prior art such as the slow growth rate of KNN-based single crystals, poor growth rate stability, small crystal size, easy introduction of impurity pollution, and low crystal quality and uniformity. Description of the Drawings:

[0020] Figure 1 It is the macroscopic morphology analysis diagram of Example 1; among them, (a) and (b) are samples obtained in step 4 of the same batch; (c) and (d) are samples obtained in step 6 of the same batch, and the compositions of the four samples (a), (b), (c), and (d) are the same.

[0021] Figure 2 is Figure 1 The enlarged macroscopic morphology analysis diagram of the sample in the white dashed line part of (d); in the figure, the central dashed area is the seed crystal, the single crystal part wraps the seed crystal, and the outside is the ceramic matrix.

[0022] Figure 3 is Figure 2 The XRD patterns of the middle seed crystal and the induced single crystal are completely consistent, with the same lattice structure and crystal orientation.

[0023] Figure 4 It is the macroscopic surface morphology analysis diagram of Example 2; among them, the central dotted area is the seed crystal, and the single crystal grows adhering to the seed crystal.

[0024] Figure 5 is Figure 4 The XRD test analysis diagram of the seed crystal and the induced single crystal in Figure 2 .

[0025] Figure 6 It is the SEM microscopic morphology analysis of the natural surface of the single crystal. Among them, (a) is the crystal sample prepared in Step 4 of Comparative Example 1 without adding Co 3 O 4 ; (b) is the crystal sample prepared in Step 4 of Example 1 with the addition of the sintering aid Co 3 O 4 . Specific implementation method:

[0026] The following is a further description of the present invention, rather than a limitation to the present invention.

[0027] Example 1:

[0028] Step 1: Primary refinement ball milling of raw materials: Dry the powder raw materials of Na 2 CO 3 , K 2 CO 3 , Nb 2 O 5 , Bi 2 O 3 , Li 2 CO 3 , BaCO 3 , ZrO 2 and Co 3 O 4 in an oven at 120°C for 12 hours to remove moisture, and then accurately weigh the dried Na respectively according to the chemical formula. After drying, Na 2 CO 3 (5.2642 g), K 2 CO 3 (6.9195 g), Nb 2 O 5 (26.4837 g), Bi 2 O 3 (0.1874 g), Li2 CO 3 (0.0303 g), BaCO 3 (0.1194 g), ZrO 2 (0.0746 g) and Co 3 O 4 (0.0803 g) powder raw materials, and refine them by ball milling. Place them in a ball milling jar made of HDPE, use zirconia balls as the grinding medium and anhydrous ethanol as the ball milling medium, and carry out ball milling in a ball mill at a speed of 410 r / min for 24 h. After ball milling, dry the raw materials at 80 °C for 10 h and sieve them through a 100-mesh sieve to obtain the primary ball-milled material.

[0029] Step 2: Pre-sintering treatment of the primary ball-milled material: Pre-sinter the primary ball-milled material obtained in Step 1 at 750 °C for 6 h to obtain the pre-sintered material.

[0030] Step 3: Secondary refinement ball milling treatment of the pre-sintered material: Carry out secondary refinement ball milling on the pre-sintered material obtained in Step 2, and after ball milling, carry out drying and sieving to finally obtain a more refined secondary ball-milled material. The conditions of secondary refinement ball milling, drying conditions, and sieving conditions are the same as those in the primary refinement ball milling in Step 1;

[0031] Step 4: Sintering treatment of the secondary ball-milled material: Press the secondary ball-milled material obtained in Step 3 into a circular green body under a pressure of 100 MPa and hold the pressure for 2 minutes. The diameter of the mold is 50 mm. Subsequently, use the seedless solid-phase method to sinter the circular green body, sinter it at 1108 °C for 21 h to obtain a dense pre-seed crystal, and at this time, carry out macroscopic surface morphology analysis on the prepared sample.

[0032] Step 5: Preparation of the seed crystal: Carefully peel the pre-seed crystal from the circular green body obtained in Step 4, and use ultrasonic cleaning for 20 minutes to remove surface growth residues and attachments. Analyze the growth surface by visual inspection, laser irradiation, XRD equipment, and SEM equipment, select a suitable pre-seed crystal as the product, then polish it along its exposed surface and growth surface, and reduce its thickness to 0.5 mm and regularize the surface size except for the growth contact surface to obtain a standardized seed crystal.

[0033] Step 6: Seed-induced growth of potassium sodium niobate-based single crystal: Bury the seed crystal obtained in Step 5 into the secondary ball-milled material prepared in Step 3, adjust the position and then press it into a seed-embedded embryo under a pressure of 100 MPa. The diameter of the mold is 50 mm. Finally, sinter it at 1106 °C for 24 h, and use the seed crystal to induce growth to prepare a homogeneous potassium sodium niobate-based single crystal, and carry out macroscopic surface morphology analysis on the sample.

[0034] In order to prove that the KNN-based single crystal grown by the method of the present invention has growth stability and can significantly increase the crystal size, macroscopic surface morphology analysis is carried out on the samples prepared in Step 4 and Step 6 respectively, such asFigure 1 As shown, where (a) and (b) are produced in step 4, and (c) and (d) are produced in step 6. By comparing Figure 1 (a) with (b), it can be clearly seen that when the seed crystal is not buried, for the small-sized single crystal grown only through steps 1 to 4, its growth shows a high degree of randomness, and the growth direction and morphology are unstable, making it impossible to effectively control the grain size and distribution. At this time, the sample shows the characteristics of random growth, with uneven distribution of growth positions, large differences in crystal sizes, and relatively small overall crystal sizes. While in Figure 1 (c) and (d), by implementing steps 5 and 6, the crystal growth of the sample after burying the seed crystal shows obvious directionality, the grain size increases significantly, and the crystal morphology is more uniform and the growth state is more stable. From Figure 1 the comparison, it can be seen that the seed crystal plays an important role in the growth of potassium sodium niobate-based single crystals in the same system, including guiding directional growth, increasing the crystal size, improving the growth stability, and reducing the growth driving force. The introduction of the seed crystal effectively reduces the competition effect caused by random nucleation, optimizes the crystal growth process, and enables the grains to grow orderly along a specific direction. In addition, the presence of the seed crystal reduces the energy barrier during crystal growth, thereby effectively increasing the growth driving force and reducing the generation of deformed grains. The seed crystal provides an efficient and stable seed template for crystal growth through its clear crystal orientation, thereby significantly increasing the growth size and quality of KNN-based single crystals, providing technical support for further optimizing the preparation process of such crystals.

[0035] To prove the structural and orientation consistency between the seed crystal and the single crystal induced to grow in the samples prepared by this method, macroscopic morphology analysis and crystal structure analysis (XRD test) were carried out, and the results are shown in Figure 2 and Figure 3 respectively. Figure 2 Figure 16 is a partial enlarged view of the sample prepared in step 6. The sample consists of three parts: the seed crystal, the grown crystal region, and the ceramic region. The single crystal induced to grow closely adheres to the seed crystal, and the interface between the two is clear without obvious separation or defects, and the induced-grown crystal shows a regular morphology. To further confirm the structural consistency between the grown crystal and the seed crystal, XRD tests were respectively carried out on the Figure 2 seed crystal and the grown single crystal in, and the test results are shown in Figure 3 Figure 19. The XRD pattern shows that the diffraction peaks of the grown crystal are exactly the same as those of the seed crystal, and no other miscellaneous peaks appear. This indicates that the induced-grown single crystal inherits the crystal structure of the seed crystal and no other miscellaneous phases are generated during the growth process, and single crystals with the same orientation structure can be induced to grow through the seed crystal.

[0036] Example 2:

[0037] Referring to Example 1, the steps not specifically described are the same as those of Example 1, except that: Co 3 O 4 content (x=0.001) and mold size (diameter is 25mm).

[0038] In order to verify the different contents of Co 3 O 4 The applicability of this method and further support the orientation consistency between the seed crystal and the induced single crystal in the process of growing KNN-based crystals by this method were tested and analyzed as follows:

[0039] 1. Macro morphology analysis: First, the overall morphology is tested macroscopically. The results are as follows: Figure 4 As shown in the figure, it can be seen that around the regular rhombus seed crystal, a single crystal with a size of 10×10 mm was induced to grow. Compared with other single crystals grown spontaneously around it, the induced single crystal is significantly larger, which further proves the superiority of the seed crystal in the system for KNN crystal growth, especially in promoting crystal growth and increasing crystal size.

[0040] 2. Crystal structure analysis (XRD test): In order to verify the consistency of the crystal structure between the induced growth crystal and the seed crystal, X-ray diffraction (XRD) tests were performed on the seed crystal and the growth crystal. The test results are as follows: Figure 5 As shown in the figure, the XRD diffraction peaks of the grown crystals are completely consistent with the diffraction peaks of the seed crystals (the characteristic peaks are of the same family), and no other impurity peaks appear. The test results show that the grown crystals inherit the crystal structure of the seed crystals, and no other impurities are generated during the growth process. This shows that the induced growth crystals have the same crystal structure as the seed crystals, ensuring the purity and consistency of the crystals.

[0041] Comparative Example 1: A method without adding Co 3 O 4 Potassium sodium niobate-based piezoelectric single crystal and preparation method thereof

[0042] Referring to Example 1, the steps not specifically described are the same as those in Example 1, except that: No sintering aid Co is added to Example 1. 3 O 4 . Figure 6 The natural surface morphology SEM analysis diagram of the single crystal sample, wherein (a) is the single crystal sample prepared in step 4 of comparative example 1 without adding Co 3 O 4 The natural surface morphology of the single crystal sample (i.e. x = 0) shows that the surface growth layer is disordered, with local bulges and large hole defects. The surface of the single crystal is even mixed with ceramic grains, showing low growth quality and high internal stress. (b) The single crystal sample prepared in step 4 of Example 1 with the addition of sintering aid Co 3 O4 The natural surface morphology of the single-crystal sample shows typical two-dimensional layer growth characteristics. The layers are regularly arranged, and the interfaces between layers are clear. The tissue density of this sample is relatively high, the surface is flat and there are no obvious pores, and the internal stress is effectively released, indicating good crystal quality. By comparing Comparative Example 1 with Example 1, it can be seen that adding Co 3 O 4 The sintering aid effectively optimizes the growth process of the single crystal, improves the surface morphology and microstructure of the single crystal, reduces pore defects and grain inclusions, thereby improving the growth quality and uniformity of the single crystal.

Claims

1. A method for preparing a potassium sodium niobate-based single crystal, characterized in that: The potassium sodium niobate-based single crystal has a size of 10 mm×10 mm×2 mm or more, and the chemical formula is: [0.997(0.996Ka 0.5 Na 0.5 NbO3-0.004LiBiO3)-0.003BaZrO3]- Co3O4, K 0.5 Na 0.5 NbO3 is used as the main material, and BaCO3, ZrO2, Co3O4, Li2CO3 and Bi2O3 are used as doping materials, wherein x represents the molar fraction of the Co element in the system, wherein 0﹤x≤0.005; the preparation method thereof comprises the following steps: 1) Preparation of pre-seed crystals: The pre-seed crystals are prepared by a seedless solid phase crystal growth method, including primary fine ball milling, pre-sintering, secondary fine ball milling and sintering; 2) Preparation of seed crystals: peeling the pre-seed crystals grown in step 1) from the round billet embryo, removing the surface growth residues and attachments, and screening out products that meet the requirements, then polishing along the exposed surface and the growth surface, and thinning the thickness to 0.5-1 mm and regularizing the size to obtain seed crystals; 3) Seed crystal induced growth of potassium sodium niobate-based single crystal: The seed crystal obtained in step 2) is embedded in the secondary ball milled material prepared by secondary refinement ball milling in the process of preparing pre-seed crystal by the seedless solid phase crystal growth method in step 1), and pressed into an embedded seed embryo at a pressure of 100-120MPa. Finally, the embedded seed embryo is sintered at 1100-1110°C for 21-24h to obtain a large-sized homogeneous potassium sodium niobate-based single crystal induced by seed crystal.

2. The preparation method according to claim 1, characterized in that: The seedless solid phase crystal growth method described in step 1) is used to prepare the pre-seed crystal, including primary fine ball milling, pre-sintering, secondary fine ball milling and sintering; the specific steps are as follows: (1) Primary refining ball milling: Dry the Na2CO3, K2CO3, Nb2O5, Bi2O3, Li2CO3, BaCO3, ZrO2 and Co3O4 powder raw materials at 120-140℃ for 12-18h, and then grind them according to the chemical formula [0.997(0.996Ka 0.5 Na 0.5 NbO3-0.004LiBiO3)-0.003BaZrO3]- Co3O4 is accurately weighed and finely ball-milled. The ball milling jar is made of HDPE, the ball milling balls are made of zirconium dioxide, the ball milling medium is anhydrous ethanol, the ball milling time is 24-48 hours, the ball milling speed is 380-450r / min, and after the ball milling, the ball milled material is dried and sieved. The drying temperature is 80-120°C, the drying time is 8-12h, and the sieving condition is to sieve with a 100-200 mesh screen. Finally, the raw material after one-time fine ball milling is obtained, which is called the primary ball milled material; (2) Pre-sintering: pre-sintering the primary ball mill obtained in step (1) at 650-800° C. for 6-8 hours to obtain a pre-sintered material; (3) Secondary ball milling: The pre-sintered material obtained in step (2) is subjected to secondary ball milling. After the ball milling, the material is dried and sieved to obtain a secondary ball milled material, which is called secondary ball milled material. The conditions for the secondary ball milling, drying conditions, and sieving conditions are the same as those for the primary ball milling in step (1). (4) Sintering: The secondary ball-milled material is pressed into a round billet at a specific pressure of 100-120 MPa and maintained at pressure for 2-5 minutes. The diameter of the mold is 25-50 mm. Then, the round billet is sintered using a seedless solid phase growth process. The sintering temperature is 1100-1110° C. and the sintering time is 21-24 hours to obtain a potassium sodium niobate-based single crystal grown according to the chemical formula.

3. The preparation method according to claim 1, characterized in that: In step 2), the method for removing the surface growth residues and attachments is ultrasonic cleaning for 15-30 minutes, and the detection includes visual inspection, laser irradiation, XRD analysis and SEM analysis.

4. The preparation method according to claim 1, characterized in that: The condition for embedding the seed crystal in step 3) is that the seed crystal is placed before pouring the secondary ball mill material into the mold, the position is adjusted, and then the two are pressed together to form an embedded seed embryo.

5. The potassium sodium niobate-based single crystal prepared by the preparation method according to any one of claims 1 to 4.

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