A high-strain low-loss lead-free piezoelectric ceramic, a preparation method and application thereof

Abstract

This application relates to a high-strain, low-loss lead-free piezoelectric ceramic, its preparation method, and its application, belonging to the field of piezoelectric ceramic technology. The lead-free piezoelectric ceramic material comprises materials with the general chemical formula (1-m)(K... x Na y Li z Bi w (Nb) a Ti b Fe c W d )O3-m(Bi 0.5 Na 0.5 The ZrO3 matrix powder satisfies 0.40≤x≤0.48, 0.40≤y≤0.48, 0.02≤z≤0.06, 0.02≤w≤0.06, 0.85≤a≤0.95, 0.05≤b≤0.12, 0.01≤c≤0.02, 0.01≤d≤0.02, and 0.03≤m≤0.10. Furthermore, 0.1~0.5wt% of MoO3 is introduced into the matrix powder. This results in low dielectric loss and heat generation under high-frequency driving conditions, as well as good temperature stability.

Description

Technical Field

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

[0002] Piezoelectric ceramics are a class of functional materials capable of converting mechanical energy into electrical energy, and they have significant application value in fields such as ultrasonic transducers, precision actuators, sensors, and advanced manufacturing equipment. For a long time, lead-containing piezoelectric ceramics, represented by lead zirconate titanate (PZT), have dominated the market due to their excellent piezoelectric properties. However, their preparation, use, and disposal processes pose lead pollution problems, making it difficult to meet increasingly stringent environmental regulations. Therefore, developing high-performance lead-free piezoelectric ceramic materials has become an important direction for development in this field.

[0003] Among numerous lead-free piezoelectric systems, KNN-based ceramics are considered one of the most promising alternative materials due to their high Curie temperature and good piezoelectric properties. To further improve their performance, existing technologies typically modify them through elemental doping, phase structure modulation, and texturing design. For example, by introducing elements such as Sb and Ta to form multi-component solid solutions, phase boundary modulation and piezoelectric response can be achieved; or by introducing precursors with specific morphologies and combining them with tape casting processes, grain orientation can be achieved, thereby obtaining higher electrostrain performance.

[0004] However, existing lead-free piezoelectric ceramics still have significant shortcomings in terms of performance and application adaptability. On the one hand, to obtain larger electroinduced strain, some technical routes employ texturing processes or complex precursor designs to enhance anisotropic response by increasing grain orientation. However, these methods typically suffer from complex process flows, limited reaction kinetics, and difficulty in controlling compositional uniformity, easily leading to insufficient phase purity or local structural defects, thus affecting the stability and consistency of the material. On the other hand, in conventional multi-doped systems, although piezoelectric performance can be improved or sintering temperature reduced to some extent, the synergistic effects between different doping elements are complex, easily introducing additional defects or second phases, thereby adversely affecting dielectric loss and insulation performance.

[0005] Furthermore, for applications such as high-frequency vibration or ultrasonic processing, more stringent performance requirements are placed on piezoelectric ceramics, such as simultaneously requiring high piezoelectric constants, low dielectric losses, and good temperature stability. However, under long-term driving conditions in high-frequency electric fields, existing material systems experience internal dielectric and mechanical losses, leading to energy accumulation as heat and a significant increase in material temperature. When the heating rate exceeds the heat dissipation rate, performance drift or even failure will occur. Although existing technologies can reduce losses through formula optimization, it is still difficult to balance low heat generation and high strain performance under high-frequency, large-displacement conditions. For example, related studies have shown that even with reduced dielectric losses through composition optimization and low-temperature co-firing processes, piezoelectric ceramics still experience significant temperature rises under certain voltage and frequency conditions, thus limiting their application under high-frequency stable conditions.

[0006] Furthermore, temperature changes also cause dynamic evolution of the domain structure and defect states within piezoelectric ceramics, leading to fluctuations in piezoelectric constant, electrostriction, and dielectric properties with temperature, exhibiting poor temperature stability. This performance instability is even more pronounced in high-frequency, high-power, or complex thermal environments, severely restricting the engineering application of lead-free piezoelectric ceramics in high-end equipment.

[0007] In summary, although existing lead-free piezoelectric ceramic technologies have made some progress in improving electro-strain or optimizing the fabrication process, they still generally suffer from problems such as limited piezoelectric strain capacity, difficulty in effectively suppressing losses and heat generation, and insufficient temperature stability. In particular, under harsh operating conditions such as high frequency and high temperature, it is difficult to achieve a synergistic improvement in performance and reliability.

[0008] Therefore, developing a lead-free piezoelectric ceramic material with high electrostriction, low loss and excellent temperature stability and its preparation method remains a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] To address the aforementioned issues, a high-strain, low-loss lead-free piezoelectric ceramic, its preparation method, and its applications are provided. The prepared piezoelectric ceramic sample has a dense microstructure with a relative density greater than 95%. The material exhibits an internal structure characterized by the coexistence of fine grains and locally larger grains, while simultaneously forming a diffusely distributed localized polarization structure. Under the influence of an electric field, this structure primarily achieves electro-strain output through localized polarization response, thereby exhibiting low dielectric loss and heating levels under high-frequency driving conditions, and possessing good temperature stability.

[0010] This application provides a high-strain, low-loss lead-free piezoelectric ceramic, wherein the lead-free piezoelectric ceramic material comprises materials with the general chemical formula (1-m)(K). x Na y Li z Bi w (Nb)a Ti b Fe c W d )O3-m(Bi 0.5 Na 0.5 The ZrO3 matrix powder satisfies 0.40≤x≤0.48, 0.40≤y≤0.48, 0.02≤z≤0.06, 0.02≤w≤0.06, 0.85≤a≤0.95, 0.05≤b≤0.12, 0.01≤c≤0.02, 0.01≤d≤0.02, 0.03≤m≤0.10, and also introduces 0.1~0.5wt% MoO3 into the matrix powder.

[0011] Among them, x+y+z+w=1, a+b+c+d=1, and satisfy x+y+z+3w+5a+4b+3c+6d is slightly lower than 6. Considering the volatilization of metal, the number of introduced oxygen vacancies can still be guaranteed to be within a controllable range.

[0012] Optional values ​​are: x=0.46, y=0.46, z=0.04, w=0.04, a=0.89, b=0.08, c=0.015, d=0.015, m=0.06.

[0013] Optionally, the amount of MoO3 added is 0.2 wt%.

[0014] This application provides a method for preparing the above-mentioned high-strain, low-loss lead-free piezoelectric ceramic, the method comprising the following steps: S1. The ingredients are prepared according to the chemical composition, and after ball milling and drying, a mixed powder is obtained. The mixed powder is then pre-calcined to obtain a pre-calcined powder. S2. After ball milling the pre-calcined powder again, add MoO3 to the pre-calcined powder and continue ball milling to make it evenly dispersed. S3. After adding the binder, the mixture is granulated, sieved, and pressed into shape to obtain a green body. S4. The green body is sintered under an asymmetric atmosphere to obtain a sintered body. S5. After preparing electrodes from the sintered body, polarization treatment is performed to obtain the lead-free piezoelectric ceramic.

[0015] In step S2, through bit A Bi 3+ / Li + Non-equivalent doping and B-site Fe 3+ W 6+ The synergistic effect introduces random fields into the lattice and induces the formation of diffusely distributed localized polarization structures, while avoiding excessive pinning of domains by strong defect dipoles. WO3, as a B-site dopant, participates in lattice solid solution, which helps to optimize the electronic structure and reduce dielectric loss.

[0016] Optionally, step S4 includes the following staged sintering process: 1) Increase the temperature to 580-620℃ at a rate of 1-3℃ / min and keep it in air for 1-3 hours; 2) Continue heating to 900~1000℃, and then introduce a hydrogen-containing reducing atmosphere and hold for 10~40 minutes; 3) Under an inert atmosphere, the temperature is raised to 1100~1150℃ and held for 1~2 hours to carry out densification sintering; 4) Annealing treatment is carried out at 800~900℃ for 0.5~2 hours in an oxygen atmosphere.

[0017] Optionally, in step 2), the reducing atmosphere is a mixture of N2 and H2, wherein the volume fraction of H2 is 3%~10%; and / or, In step 3), the inert atmosphere is N2 atmosphere.

[0018] Optionally, after sintering, the material is cooled to room temperature at a rate of 2~5℃ / min.

[0019] Optionally, in step S4, pre-fired powder is used to cover the green blank during the sintering process, with a covering thickness of 3~6mm.

[0020] Optionally, in step S1, the pre-firing temperature is 850~900℃, and the holding time is 3~5 hours; and / or, In step S2, the ball milling conditions are a rotation speed of 200-300 rpm and a time of 4-8 hours.

[0021] Optionally, the molding pressure in step S3 is 5~30MPa.

[0022] This application provides the application of the above-mentioned high-strain, low-loss lead-free piezoelectric ceramic material, or the high-strain, low-loss lead-free piezoelectric ceramic material obtained by the above-mentioned preparation method, in the preparation of piezoelectric actuators.

[0023] The beneficial effects of this application include, but are not limited to: 1. The high-strain, low-loss lead-free piezoelectric ceramic of this application, its preparation method, and its application, based on (K,Na)(Nb,Ti)O3-(Bi 0.5 Na 0.5 ZrO3 composite system, with the introduction of Li + / Bi 3+ Non-equivalent doping at the A site and Fe 3+ W 6+By introducing multi-stage doping at the B site, a random field effect is introduced into the crystal lattice, inducing the formation of a diffusely distributed localized polarization structure. This allows the material to be dominated by localized polarization response under an applied electric field, rather than relying on the traditional domain flipping mechanism. This significantly reduces internal friction loss and energy accumulation during high-frequency driving. As a result, while ensuring a large electrostrain output, the heating phenomenon can be effectively suppressed, achieving synergistic optimization between high strain and low loss, which is especially suitable for high-frequency operating conditions.

[0024] 2. Based on the high-strain, low-loss lead-free piezoelectric ceramics, their preparation method, and applications described in this application, an asymmetric atmosphere sintering process combining short-time weak reducing atmosphere treatment, rapid densification in an inert atmosphere, and subsequent low-temperature oxygen annealing is employed. By introducing, controlling, and partially eliminating oxygen vacancies and related defects at different stages, the defect structure can be effectively controlled and adjusted. On the one hand, the weak reducing stage facilitates lattice adjustment and sintering drive; on the other hand, subsequent oxygen annealing significantly reduces residual conductive defects, thereby improving the material's insulation performance while ensuring density. This process avoids the problem of uncontrollable defects in single-atmosphere sintering, enabling the material to maintain stable electrical properties under high-frequency and high-temperature conditions.

[0025] 3. Based on the high-strain, low-loss lead-free piezoelectric ceramic, its preparation method, and its application, a small amount of MoO3 is introduced into the pre-sintered powder as a functional modulation agent. This agent is then uniformly distributed at the microscale through secondary ball milling and preferentially enriched in the grain boundary region during subsequent sintering, thereby effectively controlling the grain boundary electrical properties. This grain boundary modulation mechanism can reduce the migration ability of charge carriers at grain boundaries, suppress leakage current and dielectric loss, while improving the uniformity of the internal electric field distribution and reducing the formation of local hot spots. This further reduces the heat generation level during high-frequency driving and improves the long-term stability and reliability of the device.

[0026] 4. Based on the high-strain, low-loss lead-free piezoelectric ceramic, its preparation method, and its application, this application achieves a composite microstructure with fine grains and locally larger grains through synergistic control of composition design and sintering process, resulting in high density (relative density ≥95%). The fine grains contribute to improved mechanical stability and inhibited defect propagation, while the locally larger grains enhance polarization response and improve electrostrain output. This structure achieves a balance between performance and reliability while ensuring material structural integrity, which is beneficial for the engineering application of lead-free piezoelectric ceramics under high-frequency, high-power, and complex operating conditions. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application 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 scanning electron microscope (SEM) characterization image of the KNN-BNT-Zr composite solid solution powder involved in Example 1 of this application; Figure 2 The planetary ball mill involved in this application; Figure 3 For the quasi-static d involved in this application 33 Measuring instrument; Figure 4 This refers to the capacitance tester involved in this application. Detailed Implementation

[0028] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents in the embodiments of the present application are all purchased through commercial channels.

[0029] The present application solution will be described below through specific embodiments.

[0030] Example 1 This embodiment provides a high-strain, low-loss lead-free piezoelectric ceramic and its preparation method. The chemical composition of the piezoelectric ceramic is 0.94 (K). 0.46 Na 0.46 Li 0.04 Bi 0.04 (Nb) 0.89 Ti 0.08 Fe 0.015 W 0.015 O3-0.06(Bi) 0.5 Na 0.5 ZrO3 was used, and 0.2 wt% MoO3 was introduced into the pre-calcined powder as a functional regulating agent.

[0031] 1) Raw materials and ingredients The following raw materials were selected: potassium carbonate (K2CO3), sodium carbonate (Na2CO3), lithium carbonate (Li2CO3), bismuth oxide (Bi2O3), niobium pentoxide (Nb2O5), titanium dioxide (TiO2), zirconium dioxide (ZrO2), iron oxide (Fe2O3), tungsten trioxide (WO3), and molybdenum trioxide (MoO3).

[0032] Weigh each raw material according to the above stoichiometric ratio, and prepare the batch based on 100g of powder. The amount of K2CO3 and Na2CO3 is increased by 4mol% on the basis of the theoretical amount to compensate for the loss of alkali metal volatilization during high-temperature sintering.

[0033] 2) Powder preparation Add the weighed raw materials (except MoO3) to the planetary ball mill. Figure 2In the process, zirconia balls were used as the grinding medium (ball-to-material ratio 5:1), and anhydrous ethanol was added as the dispersion medium. The mixture was ball-milled at 300 rpm for 12 hours to ensure that the components were fully mixed and refined.

[0034] After ball milling, the slurry was dried in an 80℃ forced-air drying oven for 10 hours to obtain a mixed powder. The dried powder was then placed in a covered alumina crucible and pre-fired in a box-type resistance furnace at a heating rate of 5℃ / min, reaching 880℃ and holding for 4 hours to obtain a preliminary KNN-BNT-Zr composite solid solution powder, such as... Figure 1 As shown.

[0035] 3) Relaxation structure regulation and treatment The pre-calcined powder was ball-milled again, and then 0.2 wt% MoO3 was added as a functional additive. The powder was ball-milled at 250 rpm for 6 hours in ethanol medium to ensure that each dopant element was uniformly dispersed in the powder.

[0036] 4) Molding A 5 wt% polyvinyl alcohol solution was added to the powder after secondary ball milling as a binder. After mixing evenly, the mixture was granulated by passing it through a 100-mesh sieve.

[0037] The material was formed by unidirectional pressing using a 12mm diameter mold and held under 5MPa pressure for 2 minutes to obtain a circular blank with a thickness of approximately 1.2mm.

[0038] 5) Asymmetric atmosphere-rapid sintering The obtained green body was placed in a covered alumina crucible and covered with pre-fired powder of the same composition (covering thickness of about 4 mm). The following four-stage treatment was carried out in a controlled atmosphere furnace: 5.1) Degreasing stage The temperature was increased to 600℃ at 3℃ / min and held for 2 hours in an air atmosphere to remove the organic binder. 5.2) Short-term weak reduction regulation phase Continue heating to 950℃, introduce a mixed atmosphere with a volume fraction of 95% N2 + 5% H2, and hold for 20 minutes; 5.3) Rapid heating and densification stage Under inert atmosphere conditions (H2 supply stopped, only N2 supply), the temperature was rapidly increased to 1130℃ at 8℃ / min and held for 1.5 hours to complete densification sintering in an inert atmosphere (N2 atmosphere); 5.4) Low-temperature oxygen annealing stage The atmosphere was switched to pure oxygen and annealed at 850℃ for 1 hour. After sintering, the temperature was cooled to room temperature at a rate of 3°C / min.

[0039] 6) Electrode preparation and polarization treatment The sintered ceramic sample was coated with silver paste on both sides, and electrodes were prepared by screen printing. The electrodes were then sintered at 600°C for 10 minutes to form conductive electrodes.

[0040] The sample was then placed in silicone oil and polarized for 25 minutes at 110°C with a DC electric field of 3.5 kV / mm to complete the polarization treatment, thus obtaining the lead-free piezoelectric ceramic material.

[0041] Comparative Example 1 This comparative example is basically the same as Example 1, except that (Bi) is not introduced in step 1). 0.5 Na 0.5 ZrO3, matrix powder according to (K 0.46 Na 0.46 Li 0.04 Bi 0.04 (Nb) 0.89 Ti 0.08 Fe 0.015 W 0.015 O3 preparation.

[0042] Comparative Example 2 This comparative example is basically the same as Example 1, except that Li2CO3 and Bi2O3 are not added in step 1), and the matrix powder is prepared at 0.94 (K). 0.5 Na 0.5 (Nb) 0.89 Ti 0.08 Fe 0.005 W 0.025 O3-0.06(Bi) 0.5 Na 0.5 Preparation of ZrO3.

[0043] Comparative Example 3 This comparative example is basically the same as Example 1, except that Fe2O3 and WO3 are not added in step 1), and the matrix powder is prepared at 0.94 (K). 0.465 Na 0.465 Li 0.02 Bi 0.05 (Nb) 0.9 Ti 0.1 O3-0.06(Bi) 0.5 Na 0.5 Preparation of ZrO3.

[0044] Comparative Example 4 This comparative example is basically the same as Example 1, except that MoO3 functional additive is not added in step 3).

[0045] Comparative Example 5 This comparative example is basically the same as Example 1, except that in step 1), MoO3 is added together with other raw materials for initial ball milling, while in step 3), MoO3 is not added.

[0046] Comparative Example 6 This comparative example is basically the same as Example 1, except that in step 5), no reducing atmosphere treatment is performed during the sintering process, and the entire process is carried out in an air atmosphere.

[0047] Comparative Example 7 This comparative example is basically the same as Example 1, except that in step 5), after the reducing atmosphere treatment, it is directly switched to an oxygen atmosphere for sintering treatment, without the inert atmosphere densification stage.

[0048] Comparative Example 8 This comparative example is basically the same as Example 1, except that the oxygen annealing stage is omitted in step 5), and the sintering is directly cooled to room temperature after completion.

[0049] Comparative Example 9 This comparative example is basically the same as Example 1, except that the reducing atmosphere holding time in step 5.2) is extended from 20 minutes to 2 hours.

[0050] Test Example 1 Performance tests were conducted on the products obtained in the examples and comparative examples, and the test results are shown in Table 1 below.

[0051] The test items include the following: To characterize the electrostrain properties of the material, a ferroelectric testing system was used to perform strain-electric field (SE) tests on the samples. Silver electrodes were sintered on both sides of the sample, and a triangular wave electric field (frequency 1 Hz) was applied at room temperature. The electric field strength was gradually increased to a set value (4 kV / mm), and the SE curve was recorded. The maximum strain value was taken as the maximum electrostrain S. max (Unit: %). This indicator reflects the displacement output capability of a material under the action of an electric field and is used to evaluate the improvement effect of piezoelectric strain performance.

[0052] To characterize the energy loss of the material, the dielectric loss tanδ was measured using a precision LCR meter at room temperature and 1 kHz. This parameter reflects the degree of energy dissipation of the material during the application of an electric field. Figure 4The lower the tanδ, the smaller the material loss. Furthermore, the sample was continuously driven at a certain frequency (5kHz) and electric field strength (2 kV / mm). The temperature change was recorded after a certain time (10 min) using an infrared thermometer or thermocouple, and the temperature rise ΔT (in °C) was calculated to directly evaluate the material's heating level under high-frequency driving conditions. All tests were performed at the corresponding standard frequency conditions.

[0053] To analyze the conductivity and defects of the material, a voltage (0~500V) was applied to the sample at room temperature using a source meter, the current was recorded, and the leakage current density J (unit: A / cm²) was calculated. 2 This index is used to characterize the internal electrical conductivity defects and electrical insulation properties of a material. To evaluate the temperature stability of the material, the dt of the sample before and after heat treatment is measured. 33 value( Figure 3 ), and calculate d 33 Retention rate (in %), which is the percentage of time taken after holding at a certain temperature (150℃) and then cooling to room temperature, followed by a measurement of the retention rate (d). 33 And compare it with the initial value.

[0054] The relative density (in %) of the samples was measured using the Archimedes method to assess the compactness of the material.

[0055] Table 1. Performance test results of the examples and comparative products.

[0056] Table 1 (continued)

[0057] As can be seen from Table 1, Example 1 outperforms all the comparative examples in overall performance, especially in terms of electrostrain, dielectric loss and temperature rise.

[0058] First, regarding electrostriction, the maximum electrostriction S in Example 1 is... max The result reached 0.185%, which is significantly higher than Comparative Example 1 and Comparative Example 3, indicating that by constructing the KNN-BNT-Zr composite system and introducing Fe / W synergistic doping, the electro-strain response capability of the material can be significantly improved.

[0059] Regarding dielectric loss, the tanδ of Example 1 is 0.018, significantly lower than that of the comparative examples, especially compared to Comparative Example 4 without MoO3 and Comparative Example 5 with MoO3 added beforehand. This further demonstrates that introducing MoO3 after pre-firing can effectively reduce the energy loss of the material. Furthermore, the temperature rise ΔT of Example 1 is only 12.5℃, significantly lower than that of the comparative examples, indicating that the material has a lower heat generation level under high-frequency driving conditions, verifying the technical effectiveness of this application in suppressing heat generation.

[0060] In terms of leakage current density, J in Example 1 is 1.2E-6 A / cm. 2 The value is significantly lower than that of the other pairs, indicating that this application effectively reduces internal conductive defects in the material and improves insulation performance through doping design and atmosphere control. Furthermore, regarding temperature stability, the d value of Example 1 is significantly lower than that of the other pairs. 33 The retention rate reached 92.3%, significantly better than the comparative sample, indicating that the material can maintain relatively stable piezoelectric properties under temperature changes. The relative density of each sample was above 95%, indicating that the materials all have good density, eliminating the influence of density differences on performance.

[0061] Comparative Example 5 shows that adding MoO3 during the pre-calcination stage can lead to solid-phase reactions or uneven distribution, thereby weakening its grain boundary regulation effect and causing a decline in material properties. Furthermore, Comparative Examples 6-9 demonstrate that atmosphere control and reduction time have a significant impact on the performance of the prepared products.

[0062] In summary, this application achieves a comprehensive optimization effect of improved electro-strain, reduced dielectric loss, suppressed heat generation, and improved temperature stability through the synergistic effect of composition design, additive introduction method, and asymmetric atmosphere sintering process.

[0063] 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-strain, low-loss lead-free piezoelectric ceramic, characterized in that, The lead-free piezoelectric ceramic material comprises materials with the general chemical formula (1-m)(K) x Na y Li z Bi w (Nb) a Ti b Fe c W d )O3-m(Bi 0.5 Na 0.5 The ZrO3 matrix powder satisfies 0.40≤x≤0.48, 0.40≤y≤0.48, 0.02≤z≤0.06, 0.02≤w≤0.06, 0.85≤a≤0.95, 0.05≤b≤0.12, 0.01≤c≤0.02, 0.01≤d≤0.02, 0.03≤m≤0.10, and also introduces 0.1~0.5wt% MoO3 into the matrix powder.

2. The high-strain, low-loss lead-free piezoelectric ceramic according to claim 1, characterized in that, x=0.46, y=0.46, z=0.04, w=0.04, a=0.89, b=0.08, c=0.015, d=0.015, m=0.

06.

3. The high-strain, low-loss lead-free piezoelectric ceramic according to claim 1, characterized in that, The amount of MoO3 added is 0.2 wt%.

4. The method for preparing high-strain, low-loss lead-free piezoelectric ceramics according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: S1. The ingredients are prepared according to the chemical composition, and after ball milling and drying, a mixed powder is obtained. The mixed powder is then pre-calcined to obtain a pre-calcined powder. S2. After ball milling the pre-calcined powder again, add MoO3 to the pre-calcined powder and continue ball milling to make it evenly dispersed. S3. After adding the binder, the mixture is granulated, sieved, and pressed into shape to obtain a green body. S4. The green body is subjected to asymmetric atmosphere sintering treatment to obtain a sintered body; S5. After preparing electrodes from the sintered body, polarization treatment is performed to obtain the lead-free piezoelectric ceramic.

5. The method for preparing high-strain, low-loss lead-free piezoelectric ceramics according to claim 4, characterized in that, Step S4 includes the following staged sintering process: 1) Increase the temperature to 580-620℃ at a rate of 1-3℃ / min and keep it in air for 1-3 hours; 2) Continue heating to 900~1000℃, and then introduce a hydrogen-containing reducing atmosphere and hold for 10~40 minutes; 3) Under an inert atmosphere, the temperature is raised to 1100~1150℃ and held for 1~2 hours to carry out densification sintering; 4) Annealing treatment is carried out at 800~900℃ for 0.5~2 hours in an oxygen atmosphere.

6. The method for preparing high-strain, low-loss lead-free piezoelectric ceramics according to claim 5, characterized in that, In step 2), the reducing atmosphere is a mixture of N2 and H2, wherein the volume fraction of H2 is 3%~10%; and / or, In step 3), the inert atmosphere is N2 atmosphere.

7. The method for preparing high-strain, low-loss lead-free piezoelectric ceramics according to claim 5, characterized in that, After sintering, cool to room temperature at a rate of 2~5℃ / min.

8. The method for preparing high-strain, low-loss lead-free piezoelectric ceramics according to claim 4, characterized in that, In step S4, pre-fired powder is used to cover the green blank during the sintering process, with a covering thickness of 3-6 mm.

9. The method for preparing high-strain, low-loss lead-free piezoelectric ceramics according to claim 4, characterized in that, In step S1, the pre-firing temperature is 850~900℃, and the holding time is 3~5 hours; and / or, In step S2, the ball milling conditions are a rotation speed of 200-300 rpm and a time of 4-8 hours.

10. The application of the high-strain, low-loss lead-free piezoelectric ceramic material as described in any one of claims 1 to 3, or the high-strain, low-loss lead-free piezoelectric ceramic material obtained by the preparation method as described in any one of claims 4 to 9, in the preparation of piezoelectric actuators.

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