A high-stability, high-strain lead-free piezoelectric ceramic and its preparation method

Abstract

This application discloses a high-stability, high-strain lead-free piezoelectric ceramic and its preparation method, belonging to the field of piezoelectric ceramic technology. The general chemical formula of the lead-free piezoelectric ceramic is: 0.975K 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-mBi 0.5 Na 0.5 Zr 1‑y (Mg 1 / 3 Zn 2 / 3 ) y O3-nCaTi 0.73 Sn 0.27 O3-xwt%SiC; where 0.005≤m≤0.010, 0.015≤n≤0.020, 0.02≤x≤0.06, 0.26≤y≤0.32, and m+n=0.025. This novel lead-free piezoelectric ceramic can alleviate the problems of lattice distortion and uneven internal stress, resulting in higher uniformity of grain growth in the piezoelectric ceramic. This improves the piezoelectric properties, mechanical properties, and piezoelectric stability of the piezoelectric ceramic, enabling long-term reliable operation.

Description

Technical Field

[0001] This application relates to a high-stability, high-strain lead-free piezoelectric ceramic and its preparation method, belonging to the field of piezoelectric ceramic technology. Background Technology

[0002] Piezoelectric ceramics are one of the mainstream materials in the field of functional ceramics. They are functional ceramic materials that can convert mechanical energy and electrical energy into each other, and they have been widely used in devices such as piezoelectric sensors, actuators, transducers and filters.

[0003] Currently, the most widely studied crystal structure for piezoelectric ceramics is the perovskite structure. Driven by the need for environmental protection, current research focuses more on the development of lead-free piezoelectric ceramics, among which potassium sodium niobate (KNN)-based piezoelectric ceramics are one of the most promising systems for application.

[0004] Pure KNN-based piezoelectric matrices are formed by sintering three metal oxides: K₂O, Na₂O, and Nb₂O₅. However, they suffer from limited piezoelectric properties and poor temperature stability, making them unsuitable for mid- to high-end applications. Therefore, to optimize the performance of pure KNN-based piezoelectric matrices, the industry commonly employs doping techniques, with Sb (antimony) and Ta (tantalum) doping being one of the mainstream modification methods, achieving improved piezoelectric properties. However, the applicant discovered that the introduction of Sb and Ta doping... 5+ Ta 5+ The two ions and the original Nb in the KNN matrix 5+ The ionic radii of the two elements are quite different. When these two elements are doped, it will cause large lattice distortion and uneven internal stress distribution. This defect causes the piezoelectric ceramic to degrade rapidly when it is used in high-temperature cycles, and it cannot meet the requirements of long-term reliable operation. Summary of the Invention

[0005] To address the aforementioned issues, a high-stability, high-strain lead-free piezoelectric ceramic is provided. This ceramic improves upon existing KNN-Sb-Ta-based piezoelectric ceramics, mitigating lattice distortion and internal stress inhomogeneity. This results in higher grain growth uniformity, thereby enhancing the piezoelectric properties, mechanical properties, and piezoelectric stability of the ceramic, enabling long-term reliable operation.

[0006] According to one aspect of this application, a high-stability, high-strain lead-free piezoelectric ceramic is provided, the lead-free piezoelectric ceramic having the general chemical formula: 0.975K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-mBi 0.5 Na 0.5 Zr1-y (Mg 1 / 3 Zn 2 / 3 )yO3-nCaTi 0.73 Sn 0.27 O3-xwt%SiC; Where 0.005≤m≤0.010, 0.015≤n≤0.020, 0.02≤x≤0.06, 0.26≤y≤0.32, and m+n=0.025.

[0007] This application achieves excellent piezoelectric ceramics with superior piezoelectric properties, mechanical properties, and piezoelectric stability by precisely controlling the above-mentioned components within this range, mainly by utilizing Bi³⁺. + Zr 4+ Mg² + Zn² + Ca² + Ti 4+ Sn 4+ The introduction of plasma initially fills the lattice defects caused by Sb and Ta doping, thus mitigating lattice distortion and reducing internal stress inhomogeneity. Further, by incorporating a specific amount of SiC, uniform doping is achieved in the piezoelectric ceramic. This inhibits abnormal grain growth, promoting uniform and stable grain growth, resulting in a neat, uniform, and highly consistent grain arrangement, thereby improving the piezoelectric and mechanical properties of the ceramic. The synergy between the piezoelectric ceramic components and SiC also enhances the electrostrictive properties of the ceramic under an electric field, improving output performance and reducing losses and hysteresis, thereby increasing stability under high temperatures and long-term use, and achieving long-term stable operation. If the SiC doping amount is too low, the above effects are not significant; however, excessive SiC doping can also have adverse consequences. Excess SiC will agglomerate in the matrix, leading to interface defects and excessive local lattice distortion, which is detrimental to improving piezoelectric performance and stability.

[0008] Alternatively, x = 0.04, y = 0.28.

[0009] The value of x above represents the optimal doping amount for SiC, which can both suppress abnormal grain growth and prevent agglomeration, allowing for uniform dispersion in the matrix to alleviate lattice distortion. The value of y represents Mg²⁺. + Zn² + The doping at this value optimizes the performance of piezoelectric ceramics, maximizing their compatibility with the matrix lattice structure, reducing internal stress, and preventing stress concentration.

[0010] Optionally, m:n = 1:1.5.

[0011] Bi in the piezoelectric ceramic of this application0.5 Na 0.5 Zr 1-y (Mg 1 / 3 Zn 2 / 3 )yO3 and CaTi 0.73 Sn 0.27 O3 has a synergistic effect. m and n represent the content of the two components mentioned above. When m and n are in the above ratio, the internal lattice structure of the piezoelectric ceramic is the most stable and uniform, and the internal stress caused by lattice differences is the smallest. This can further improve the piezoelectric and mechanical properties of the piezoelectric ceramic, and also improve the stability of the piezoelectric properties under high temperature and long-term operation. Furthermore, it can ensure that the piezoelectric ceramic has a high performance retention rate under high temperature and long-term load, and suppress performance degradation.

[0012] According to a second aspect of this application, a method for preparing the high-stability, high-strain lead-free piezoelectric ceramic as described in any of the preceding claims is provided, comprising the following steps: (1) Weigh out K2CO3, Na2CO3, Nb2O5, Sb2O3, Ta2O5, Bi2O3, ZrO2, MgO, ZnO, CaO, TiO2, and SnO2 according to the general chemical formula of lead-free piezoelectric ceramics as component A; and use SiC after surface oxidation treatment as component B. (2) Mix component A and component B, add anhydrous ethanol to disperse and grind, and obtain the first material; (3) The first material is dried, sieved, pre-fired, ground, dried and sieved again to obtain piezoelectric ceramic material; (4) The piezoelectric ceramic material is mixed with solvent, dispersant, binder and plasticizer to obtain casting slurry; (5) The cast slurry is cast, cut into sheets, stacked, hot-pressed, cut, debonded and sintered, and cooled to obtain piezoelectric ceramics.

[0013] This preparation method improves the continuity of piezoelectric ceramic preparation through grinding, pre-firing and other steps, which facilitates industrial application. Directly mixing SiC with other components for pre-firing can lead to problems with poor dispersibility and compatibility. Therefore, in step (1), the SiC component is surface-oxidized to improve its compatibility with other components and ensure that it can be uniformly dispersed in the first material, laying the foundation for subsequent suppression of abnormal grain growth.

[0014] Optionally, the preheating temperature in step (3) is 780-820℃ and the time is 3-5.5h.

[0015] The pre-firing process of this application can induce a preliminary solid-state reaction in each component of component A, thereby forming a stable intermediate phase. It can also prevent premature grain growth and facilitate the uniform and stable growth of subsequent grains.

[0016] Optionally, the debinding and sintering in step (5) is divided into five stages: In the first stage, the temperature is increased from room temperature to 150-180℃ at a rate of 1-3℃ / min and held for 50 minutes. In the second stage, the temperature is increased to 350-400℃ at a heating rate of 1-3℃ / min and held for 150min. In the third stage, the temperature is increased to 550-650℃ at a rate of 2-3℃ / min, and then held for 1.5 hours. In the fourth stage, the temperature is increased to 950-1000℃ at a heating rate of 1-3℃ / min and sintered for 1-2 hours. In the fifth stage, the temperature is increased to 1100-1120℃ at a heating rate of 3-5℃ / min and sintered for 2-4 hours.

[0017] The solvent and binder added in step (4) of this application are to improve the stability of the casting process and thus improve the physical uniformity of the piezoelectric ceramic. The first three stages of the debinding sintering in step (5) are to remove the solvent and binder. The three stages from the first stage to the third stage adopt the above-mentioned staged heat preservation process. On the one hand, it can realize the step-by-step removal of binder and solvent, avoid physical defects such as micropores and cracks in piezoelectric ceramics caused by excessive debinding, and improve the yield of piezoelectric ceramics. On the other hand, it can improve the stability of internal temperature rise of piezoelectric ceramics, reduce impurity content, and lay the foundation for uniform grain growth, thereby obtaining piezoelectric ceramics with good performance consistency in this application.

[0018] The sintering process in this application is directly completed by self-drying binder, which avoids the high brittleness defect caused by large temperature differences in piezoelectric ceramics. The fourth stage uses a lower heating rate and a lower temperature for a longer sintering time, which allows each component to gradually stabilize and undergo solid-state reactions, resulting in synchronous, stable, and uniform grain growth. This suppresses abnormal grain growth and lattice distortion, thus ensuring high grain growth uniformity in the piezoelectric ceramic. This improves the uniformity of the internal phase structure of the piezoelectric ceramic and reduces internal stress caused by differences in grain growth. The fifth stage, with its rapid heating and higher temperature sintering, ensures the stability of the grain structure while shortening the sintering time, improving growth efficiency, and further eliminating the inherent defects of the piezoelectric ceramic, thereby obtaining a highly uniform piezoelectric ceramic.

[0019] Optionally, the cooling in step (5) is: natural cooling with the furnace.

[0020] This cooling method, through slow cooling, effectively reduces the thermal stress generated by temperature gradients within the ceramic material, thereby inhibiting the initiation and propagation of microcracks and improving the density and mechanical strength of the ceramic mass. Simultaneously, natural cooling helps stabilize the defect structure and domain configuration at grain boundaries, reducing the migration rate of point defects such as oxygen vacancies, thus improving the temperature stability and time-related aging characteristics of key performance parameters such as piezoelectric constant and electromechanical coupling coefficient. Compared to rapid cooling, furnace cooling also avoids compositional segregation or phase transformation inhomogeneity caused by sudden cooling, ensuring batch-to-batch consistency and reliability of ceramic sample performance.

[0021] Optionally, the specific steps for surface oxidation treatment of SiC are as follows: In an air or oxygen atmosphere, SiC powder is heated to 1050-1100℃ and held for 2.5-3 hours. After cooling, SiC with a silicon dioxide oxide layer on the surface is obtained, which is component B.

[0022] By treating SiC powder as described above, a silicon dioxide oxide layer can be uniformly grown on the surface of SiC powder. The presence of the surface silicon dioxide oxide layer can improve the compatibility with each substance in component A, thereby improving the dispersion uniformity of component B in the first material. Furthermore, the presence of this silicon dioxide oxide layer can further promote the interfacial bonding between SiC and the matrix during the pre-firing, debinding, and sintering stages, thereby reducing the interface boundary. It also has the advantages of promoting uniform grain growth and reducing lattice distortion.

[0023] Optionally, the heating rate of SiC powder to 1050-1100℃ is 5℃ / min, and the cooling rate is natural cooling with the furnace.

[0024] The heating rate and cooling method described above for SiC powder can achieve temperature uniformity of SiC powder, avoid uneven local oxidation, thereby improving the uniformity and density of the silica layer on the surface of SiC powder, and thus enabling it to be uniformly dispersed in the matrix, achieving the above-mentioned effects.

[0025] The beneficial effects of this application include, but are not limited to: 1. Based on the high-stability, high-strain lead-free piezoelectric ceramic of this application, through a reasonable proportioning of the general chemical formula, Bi... 0.5 Na 0.5 Zr 1-y (Mg 1 / 3 Zn 2 / 3 )yO3 and CaTi 0.73 Sn 0.27 O3 can initially reduce lattice distortion and, in synergy with SiC, enhance the electrostrictive properties of piezoelectric ceramics under an electric field, thereby improving output performance and reducing losses and hysteresis. This improves stability under high temperature and long-term use, enabling long-term stable operation.

[0026] 2. The high-stability, high-strain lead-free piezoelectric ceramic according to this application is a lead-free piezoelectric ceramic system, which conforms to the trend of environmental protection development. It has a high performance retention rate under high temperature and long-term load, and is suitable for mid-to-high-end application scenarios.

[0027] 3. The preparation method of high-stability, high-strain lead-free piezoelectric ceramics according to this application has a high degree of continuity, strong operability, and is easy to promote and use on a large scale in industry, which broadens the application prospects of lead-free piezoelectric ceramics and has extremely high practical and economic value.

[0028] 4. According to the preparation method of high-stability, high-strain lead-free piezoelectric ceramics in this application, the surface oxidation treatment of SiC powder can significantly improve the compatibility of SiC component with other components, thereby improving the dispersibility of SiC powder in the first material, laying the foundation for the subsequent SiC component to reduce lattice distortion and inhibit abnormal grain growth. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a SEM image of the cross-section of the piezoelectric ceramic involved in Embodiment 1 of this application. Detailed Implementation

[0030] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0031] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application were all purchased commercially.

[0032] Unless otherwise specified, the methods used in the embodiments and comparative examples of this application are conventional methods in the prior art.

[0033] In the following examples and comparative examples, the grinding in step (2) is done with zirconium balls, and the mass ratio of zirconium balls, anhydrous ethanol and powder (total mass of component A and component B) is 2:1:1, and the grinding time is 6h; the drying temperature in step (3) is 80℃, the drying time is 8h, and the grinding is also done with zirconium balls; in step (4), the solvent is ethyl acetate, the dispersant is polyether-based high molecular weight cationic dispersant AKM0531, the binder is polyvinyl butyral, and the plasticizer is dioctyl phthalate. The mass ratio of the second material, dispersant, solvent, binder and plasticizer is 1:0.01:0.5:0.07:0.03, the hot pressing pressure is 10MPa, and the hot pressing time is 15min.

[0034] Example 1 This embodiment relates to a high-stability, high-strain lead-free piezoelectric ceramic with the general chemical formula: 0.975K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.005Bi 0.5 Na 0.5 Zr 0.74 (Mg 1 / 3 Zn 2 / 3 ) 0.26 O3-0.020CaTi 0.73 Sn 0.27 O3-0.02wt%SiC.

[0035] Its preparation method includes the following steps: (1) Weigh out K2CO3, Na2CO3, Nb2O5, Sb2O3, Ta2O5, Bi2O3, ZrO2, MgO, ZnO, CaO, TiO2, and SnO2 as component A according to the general chemical formula of lead-free piezoelectric ceramics; SiC powder was heated to 1050℃ in an air or oxygen atmosphere at a heating rate of 5℃ / min and held for 3 hours. The powder was then cooled to room temperature in the furnace to obtain SiC with a silicon dioxide oxide layer on the surface, which was used as component B. (2) Mix component A and component B, add anhydrous ethanol to disperse and grind, and obtain the first material; (3) The first material is dried, sieved, pre-fired at 780°C for 5.5 hours, ground, dried and sieved to obtain the piezoelectric ceramic material; (4) The piezoelectric ceramic material is mixed with solvent, dispersant, binder and plasticizer to obtain casting slurry; (5) The cast slurry is cast, cut into sheets, stacked, hot-pressed, cut, debonded and sintered, and then cooled to room temperature to obtain the final product; The debinding and sintering process is divided into five stages: In the first stage, the temperature is increased from room temperature to 150℃ at a rate of 3℃ / min and held for 50 minutes. In the second stage, the temperature is increased to 350℃ at a heating rate of 3℃ / min and held for 150min. In the third stage, the temperature is increased to 550℃ at a rate of 2℃ / min, and then held for 1.5 hours. In the fourth stage, the temperature was increased to 1000℃ at a heating rate of 3℃ / min and sintered for 1 hour. In the fifth stage, the temperature was increased to 1120℃ at a heating rate of 5℃ / min and sintered for 2 hours.

[0036] Example 2 This embodiment relates to a high-stability, high-strain lead-free piezoelectric ceramic with the general chemical formula: 0.975K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.010Bi 0.5 Na 0.5 Zr 0.68 (Mg 1 / 3 Zn 2 / 3 ) 0.32 O3-0.015CaTi 0.73 Sn 0.27 O3-0.06wt%SiC; Its preparation method includes the following steps: (1) Weigh out K2CO3, Na2CO3, Nb2O5, Sb2O3, Ta2O5, Bi2O3, ZrO2, MgO, ZnO, CaO, TiO2, and SnO2 as component A according to the general chemical formula of lead-free piezoelectric ceramics; SiC powder was heated to 1100℃ in an air or oxygen atmosphere at a heating rate of 5℃ / min and held for 2.5h. The powder was then cooled to room temperature in the furnace to obtain SiC with a silicon dioxide oxide layer on the surface, which was used as component B. (2) Mix component A and component B, add anhydrous ethanol to disperse and grind, and obtain the first material; (3) The first material is dried, sieved, pre-fired at 820°C for 3 hours, ground, dried and sieved to obtain the piezoelectric ceramic material; (4) The piezoelectric ceramic material is mixed with solvent, dispersant, binder and plasticizer to obtain casting slurry; (5) The cast slurry is cast, cut into sheets, stacked, hot-pressed, cut, debonded and sintered, and then cooled to room temperature to obtain the final product; The debinding and sintering process is divided into five stages: In the first stage, the temperature is increased from room temperature to 180℃ at a rate of 1℃ / min and held for 50 minutes. In the second stage, the temperature is increased to 400℃ at a heating rate of 1℃ / min and held for 150min. In the third stage, the temperature is increased to 650℃ at a rate of 3℃ / min, and then held for 1.5 hours. In the fourth stage, the temperature was increased to 950℃ at a heating rate of 1℃ / min and sintered for 2 hours. In the fifth stage, the temperature was increased to 1100℃ at a heating rate of 3℃ / min and sintered for 4 hours.

[0037] Example 3 This embodiment relates to a high-stability, high-strain lead-free piezoelectric ceramic with the general chemical formula: 0.975K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.010Bi 0.5 Na 0.5 Zr 0.72 (Mg 1 / 3 Zn 2 / 3 ) 0.28 O3-0.015CaTi 0.73 Sn 0.27 O3-0.04wt%SiC.

[0038] Its preparation method includes the following steps: (1) Weigh out K2CO3, Na2CO3, Nb2O5, Sb2O3, Ta2O5, Bi2O3, ZrO2, MgO, ZnO, CaO, TiO2, and SnO2 as component A according to the general chemical formula of lead-free piezoelectric ceramics; SiC powder was heated to 1100℃ in an air or oxygen atmosphere at a heating rate of 5℃ / min and held for 2.5h. The powder was then cooled to room temperature in the furnace to obtain SiC with a silicon dioxide oxide layer on the surface, which was used as component B. (2) Mix component A and component B, add anhydrous ethanol to disperse and grind, and obtain the first material; (3) The first material is dried, sieved, pre-fired at 800°C for 4 hours, ground, dried and sieved to obtain the piezoelectric ceramic material; (4) The piezoelectric ceramic material is mixed with solvent, dispersant, binder and plasticizer to obtain casting slurry; (5) The cast slurry is cast, cut into sheets, stacked, hot-pressed, cut, debonded and sintered, and then cooled to room temperature to obtain the final product; The debinding and sintering process is divided into five stages: In the first stage, the temperature is increased from room temperature to 170℃ at a heating rate of 2℃ / min and held for 50min. In the second stage, the temperature is increased to 390℃ at a heating rate of 2℃ / min and held for 150min. In the third stage, the temperature is increased to 600℃ at a rate of 3℃ / min, and then held for 1.5 hours. In the fourth stage, the temperature was increased to 990℃ at a heating rate of 2℃ / min and sintered for 1.5 hours. In the fifth stage, the temperature was increased to 1110℃ at a heating rate of 4℃ / min and sintered for 3 hours.

[0039] Example 4 The difference between this embodiment and Embodiment 3 is that the general chemical formula of the lead-free piezoelectric ceramic is: 0.975K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.010Bi 0.5 Na 0.5 Zr 0.70 (Mg 1 / 3 Zn 2 / 3 ) 0.30 O3-0.015CaTi 0.73 Sn 0.27 O3-0.06wt%SiC, that is, in this embodiment, x is 0.06, y is 0.30, and the rest is the same as in embodiment 3.

[0040] Example 5 The difference between this embodiment and embodiment 3 is that the debinding and sintering in step (5) is divided into four stages: In the first stage, the temperature is increased from room temperature to 350℃ at a heating rate of 2℃ / min and held for 200min. In the second stage, the temperature is increased to 600℃ at a rate of 3℃ / min and held for 1.5 hours. In the third stage, the temperature was increased to 990℃ at a heating rate of 2℃ / min and sintered for 1.5h. In the fourth stage, the temperature was increased to 1010℃ at a heating rate of 4℃ / min and sintered for 3 hours. The rest was the same as in Example 3.

[0041] Example 6 The difference between this embodiment and embodiment 3 is that the debinding and sintering in step (5) is divided into four stages: In the first stage, the temperature is increased from room temperature to 170℃ at a heating rate of 2℃ / min and held for 50min. In the second stage, the temperature is increased to 390℃ at a heating rate of 2℃ / min and held for 150min. In the third stage, the temperature is increased to 600℃ at a rate of 3℃ / min, and then held for 1.5 hours. In the fourth stage, the temperature was increased to 1110°C at a heating rate of 2°C / min and sintered for 4.5 hours. The rest of the process was the same as in Example 3.

[0042] Example 7 The difference between this embodiment and embodiment 3 is that the heating rate for surface oxidation treatment of SiC is 10℃ / min, while the rest is the same as in embodiment 3.

[0043] Comparative Example 1 The difference between this comparative example and Example 3 is that the chemical formula of the lead-free piezoelectric ceramic is: 0.975K.0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.010Bi 0.5 Na 0.5 Zr 0.72 (Mg 1 / 3 Zn 2 / 3 ) 0.28 O3-0.015CaTi 0.73 Sn 0.27 O3, meaning that SiC is not added to the piezoelectric ceramic in this comparative example, and the rest is the same as in Example 3.

[0044] Comparative Example 2 The difference between this comparative example and Example 3 is that the chemical formula of the lead-free piezoelectric ceramic is: 0.975K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.010Bi 0.5 Na 0.5 Zr 0.72 (Mg 1 / 3 Zn 2 / 3 ) 0.28 O3-0.015CaTi 0.73 Sn 0.27 O3-0.08wt%SiC, that is, the mass fraction of SiC added to the piezoelectric ceramic in this comparative example is 0.08wt%, and the rest is the same as in Example 3.

[0045] Comparative Example 3 The difference between this comparative example and Example 3 is that the chemical formula of the lead-free piezoelectric ceramic is: 0.965K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.020Bi 0.5 Na 0.5 Zr 0.72 (Mg 1 / 3 Zn 2 / 3 ) 0.28 O3-0.015CaTi 0.73 Sn 0.27 O3-0.04wt%SiC, the rest is the same as in Example 3.

[0046] Comparative Example 4 The difference between this comparative example and Example 3 is that the chemical formula of the lead-free piezoelectric ceramic is: 0.975K. 0.48Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.010Bi 0.5 Na 0.5 Zr 0.64 (Mg 1 / 3 Zn 2 / 3 ) 0.36 O3-0.015CaTi 0.73 Sn 0.27 O3-0.04wt%SiC, the rest is the same as in Example 3.

[0047] Comparative Example 5 The difference between this comparative example and Example 3 is that the chemical formula of the lead-free piezoelectric ceramic is: 0.975K. 0.48 Na 0.52 Nb0. 94 Sb0. 03 Ta0. 03 O3-0.020Bi 0.5 Na 0.5 Zr 0.72 (Mg 1 / 3 Zn 2 / 3 ) 0.28 O3-0.005CaTi 0.73 Sn 0.27 O3-0.04wt%SiC, the rest is the same as in Example 3.

[0048] Test Example 1 Initial performance tests were conducted on the aforementioned lead-free piezoelectric ceramics, and the test results are shown in Table 1.

[0049] Figure 1 This is a SEM image of the cross-section of the piezoelectric ceramic involved in Embodiment 1 of this application, magnified at 5000x. Figure 1 As can be seen, the cross-section of the piezoelectric ceramic exhibits typical polycrystalline sintered body characteristics, with irregular blocky grains as the main component, uniform size distribution, and no obvious abnormally large grains; the grains are tightly bonded, with clear and continuous grain boundaries, and no obvious pores, microcracks, or grain boundary phase enrichment defects. This indicates that the piezoelectric ceramic material and sintering process of this application have achieved a high-density and uniform microstructure of the piezoelectric ceramic, providing a microstructure basis for the material's excellent piezoelectric properties, mechanical stability, and long-term reliability.

[0050] d in Table 1 33denoted by ρ, the larger the value, the better the piezoelectric performance of the piezoelectric ceramic; Kp is the electromechanical coupling coefficient, the larger the value, the better the piezoelectric performance of the piezoelectric ceramic; Qm is the mechanical quality factor, the higher the value, the higher the energy storage efficiency of the piezoelectric ceramic, the smaller the energy loss, and the better the piezoelectric performance; Tanδ is the dielectric loss, the smaller the value, the smaller the dielectric loss, and the better the piezoelectric performance.

[0051] Table 1

[0052] Test Example 2 The above-mentioned lead-free piezoelectric ceramics were subjected to 168 thermal shock cycles after being kept at -40℃ for 30 minutes and at 150℃ for 30 minutes. Then, their piezoelectric properties were tested, and the rate of decrease in piezoelectric constant and electromechanical coupling coefficient were calculated. The test results are shown in Table 2.

[0053] In Table 2, the piezoelectric constant decrease rate is calculated as [(initial piezoelectric constant - piezoelectric constant after 168 thermal shocks) / initial piezoelectric constant] × 100%. The smaller the piezoelectric constant decrease rate, the better the long-term stability of the piezoelectric ceramic. Similarly, the electromechanical coupling coefficient decrease rate is calculated as [(initial electromechanical coupling coefficient - electromechanical coupling coefficient after 168 thermal shocks) / initial electromechanical coupling coefficient] × 100%. The smaller the electromechanical coupling coefficient decrease rate, the better the long-term stability of the piezoelectric ceramic.

[0054] Table 2

[0055] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A high-stability, high-strain lead-free piezoelectric ceramic, characterized in that, The general chemical formula of the lead-free piezoelectric ceramic is: 0.975K. 0.48 Na 0.52 Nb 0.94 Sb 0.03 Ta 0.03 O3-mBi 0.5 Na 0.5 Zr 1-y (Mg 1 / 3 Zn 2 / 3 ) y O3-nCaTi 0.73 Sn 0.27 O3-xwt%SiC; Where 0.005≤m≤0.010, 0.015≤n≤0.020, 0.02≤x≤0.06, 0.26≤y≤0.32, and m+n=0.

025.

2. The high-stability, high-strain lead-free piezoelectric ceramic according to claim 1, characterized in that, x=0.04, y=0.

28.

3. The high-stability, high-strain lead-free piezoelectric ceramic according to claim 2, characterized in that, m:n = 1:1.

5.

4. The method for preparing high-stability, high-strain lead-free piezoelectric ceramics according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Weigh K2CO3, Na2CO3, Nb2O5, Sb2O3, Ta2O5, Bi2O3, ZrO2, MgO, ZnO, CaO, TiO2, and SnO2 according to the general chemical formula of lead-free piezoelectric ceramics as component A; and use SiC as component B after surface oxidation treatment. (2) Mix component A and component B, add anhydrous ethanol to disperse and grind, and obtain the first material; (3) The first material is dried, sieved, pre-fired, ground, dried and sieved again to obtain the piezoelectric ceramic material; (4) The piezoelectric ceramic material is mixed with solvent, dispersant, binder and plasticizer to obtain casting slurry; (5) The cast slurry is cast, cut into sheets, stacked, hot-pressed, cut, debonded and sintered, and cooled to obtain piezoelectric ceramics.

5. The preparation method according to claim 4, characterized in that, The preheating temperature in step (3) is 780-820℃ and the time is 3-5.5h.

6. The preparation method according to claim 4, characterized in that, Step (5) of debinding and sintering includes five stages: In the first stage, the temperature is increased from room temperature to 150-180℃ at a rate of 1-3℃ / min and held for 50 minutes. In the second stage, the temperature is increased to 350-400℃ at a heating rate of 1-3℃ / min and held for 150min. In the third stage, the temperature is increased to 550-650℃ at a rate of 2-3℃ / min, and then held at that temperature for 1.5 hours. In the fourth stage, the temperature is increased to 950-1000℃ at a heating rate of 1-3℃ / min and sintered for 1-2 hours. In the fifth stage, the temperature is increased to 1100-1120℃ at a heating rate of 3-5℃ / min and sintered for 2-4 hours.

7. The preparation method according to claim 4, characterized in that, The cooling in step (5) is: natural cooling with the furnace.

8. The preparation method according to claim 4, characterized in that, The specific steps for surface oxidation treatment of SiC are as follows: In an air or oxygen atmosphere, SiC powder is heated to 1050-1100℃ and held for 2.5-3 hours. After cooling, SiC with a silicon dioxide oxide layer on the surface is obtained, which is component B.

9. The preparation method according to claim 8, characterized in that, The SiC powder was heated to 1050-1100℃ at a rate of 5℃ / min, and cooled naturally in the furnace.

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