High-density lead-free piezoelectric ceramic, preparation method and application thereof

Abstract

This application relates to a high-density lead-free piezoelectric ceramic, its preparation method, and its application, belonging to the field of piezoelectric ceramic technology. The lead-free piezoelectric ceramic is denoted as (1-x)(K). a Na b Ag c (Nb) p Ta q Sb r Zr s O3-x(Bi) 0.5 Na 0.5 TiO3, wherein 0.45≤a≤0.50, 0.44≤b≤0.48, 0.04≤c≤0.08, and a+b+c=1; 0.88≤p≤0.92, 0.04≤q≤0.08, 0.01≤r≤0.03, 0.01≤s≤0.03, and p+q+r+s=1; 0.005≤x≤0.02; and by introducing 0.2~1.0wt% lithium boron aluminum silicon glass additive and 0.1~0.5mol% MnO2, can maintain high density while exhibiting excellent piezoelectric properties, low dielectric loss, and good temperature stability.

Description

Technical Field

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

[0002] Piezoelectric ceramics are important functional materials capable of converting electrical energy into mechanical energy, and are widely used in sensors, actuators, and transducers. For a long time, lead-containing piezoelectric ceramics, represented by PZT, have dominated due to their excellent piezoelectric properties. However, their preparation, use, and disposal pose environmental pollution and health risks. Developing high-performance lead-free piezoelectric ceramics has become an important direction for development in this field.

[0003] Among numerous lead-free systems, perovskite structures, represented by KNN, are considered one of the most promising alternative systems due to their high Curie temperature and excellent piezoelectric response. Existing techniques typically construct rhombohedral-tetragonal coexisting structures by introducing multi-component dopants such as Li, Sb, and Ta, thereby optimizing phase boundaries and improving piezoelectric performance. Simultaneously, by introducing small amounts of components such as BiFeO3, which are dissolved into the crystal lattice, lattice distortion is induced and the domain flipping energy barrier is lowered, thus improving electrical performance.

[0004] However, the aforementioned doping strategies still have significant limitations in practical applications. On the one hand, components such as BiFeO3 exhibit a threshold effect during doping. When the doping amount exceeds a certain range, it introduces a large number of oxygen vacancies and defect clusters, inhibiting domain wall movement and leading to increased dielectric loss, which in turn significantly reduces piezoelectric performance. On the other hand, doping elements with large differences in ionic radius are prone to causing local structural distortion and reduced sintering activity after entering the crystal lattice, resulting in decreased material density and the formation of residual porosity, thereby affecting long-term service stability.

[0005] In addition, another type of existing technology is mainly based on the BF-BT system, which introduces a second phase such as CaSnO3 to regulate grain size and domain behavior in order to improve Curie temperature and overall performance. However, this type of material still mainly relies on component substitution as the main regulation method, and its modification mechanism mainly depends on grain refinement and domain structure constraint. It does not pay enough attention to defect control and grain boundary structure adjustment during the sintering densification process, and it is still difficult to achieve a synergistic improvement in high density and structural stability.

[0006] Overall, existing lead-free piezoelectric ceramic technologies mainly focus on single-doping or simple multi-doping strategies to improve performance by controlling the crystal structure or phase boundary characteristics. However, they generally suffer from the following problems: First, the doping methods are relatively simple, which can easily disturb the matrix crystal structure, leading to increased defect concentration and decreased density. Second, there is a lack of fine control over the liquid phase behavior and grain boundary structure during sintering, making it difficult to achieve high-density preparation. Third, the material has insufficient structural stability under temperature changes or long-term service conditions, resulting in significant degradation of piezoelectric performance.

[0007] Therefore, there is an urgent need to develop a new lead-free piezoelectric ceramic system that, while maintaining the high-voltage performance advantages of the KNN-based system, achieves synergistic optimization of lattice structure stabilization, effective defect suppression, and sintering densification process through a multi-scale synergistic control strategy, thereby simultaneously improving the material's density, temperature stability, and long-term service reliability. Summary of the Invention

[0008] To address the aforementioned issues, a high-density lead-free piezoelectric ceramic material, its preparation method, and its applications are provided. By introducing a low-melting-point glass additive, particle rearrangement and porosity elimination can be promoted during sintering, thereby significantly improving the density of the ceramic material and inhibiting abnormal grain growth. Simultaneously, MnO2 is used to regulate the defect structure, reducing leakage current loss and improving temperature stability. Furthermore, (Bi) 0.5 Na 0.5 The introduction of TiO3 component improves the domain response characteristics, giving the material better polarization behavior under an applied electric field.

[0009] This application provides a high-density lead-free piezoelectric ceramic, the general chemical formula of which is (1-x)(K). a Na b Ag c (Nb) p Ta q Sb r Zr s )O3-x(Bi 0.5 Na 0.5 TiO3, where 0.45≤a≤0.50, 0.44≤b≤0.48, 0.04≤c≤0.08, and a+b+c=1; 0.88≤p≤0.92, 0.04≤q≤0.08, 0.01≤r≤0.03, 0.01≤s≤0.03, and p+q+r+s=1; 0.005≤x≤0.02; In the lead-free piezoelectric ceramic, 0.2~1.0wt% of lithium boron aluminum silicon glass additive and 0.1~0.5mol% of MnO2 are introduced as defect control agents. The lithium boron aluminum silicon glass additive is a quaternary oxide system of Li2O-B2O3-SiO2-Al2O3.

[0010] To address the insufficient density problem in existing technologies, this application introduces lithium boron aluminum silicon glass additives, which can promote particle rearrangement and porosity elimination during sintering; to address the problems of high defect concentration and large leakage loss, defect regulation is achieved by introducing MnO2 to suppress oxygen vacancy migration; to address the problems of insufficient piezoelectric performance and temperature stability, (Bi) 0.5 Na 0.5 TiO3, combined with a staged polarization process, achieves optimized domain structure. Among them, MnO2, as a defect modulator, can suppress the disordered migration of oxygen vacancies by adjusting the defect concentration and its distribution state, thereby reducing leakage current density.

[0011] The sum of a+b+c+5p+5q+5r+4s is close to 6 (Sb). 3+ Become Sb 5+ This ensures that even with the volatilization of some metal elements, a controllable number of oxygen vacancies can still be introduced, preventing the introduction of too many oxygen vacancies from causing a deterioration in the performance of the piezoelectric ceramic.

[0012] Optional values ​​are a=0.48, b=0.46, c=0.06, p=0.90, q=0.06, r=0.02, s=0.02, and x=0.01.

[0013] Optionally, the molar ratio of each component in the lithium borosilicate glass additive is Li2O:B2O3:SiO2:Al2O3=(20~30):(30~40):(15~25):(15~25).

[0014] Optionally, the glass transition temperature of the lithium boron aluminum silicon glass additive is 450~500℃, the softening temperature is 550~600℃, and the particle size is 0.5~2μm.

[0015] This application provides a method for preparing the above-mentioned high-density 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, which is then pre-calcined to obtain a pre-calcined powder; S2. After pulverizing the pre-calcined powder, add (Bi) 0.5 Na 0.5 The raw materials required for TiO3 composition and MnO2 undergo secondary ball milling. S3. Add lithium boron aluminum silicon glass additive to the obtained powder and continue ball milling to make it evenly dispersed; S4. Add binder, granulate, sieve and press to form green body; S5. The green blank is sintered to obtain a sintered body; S6. After preparing electrodes from the sintered body, perform staged coupling polarization treatment to obtain the lead-free piezoelectric ceramic material.

[0016] Optionally, step S5 includes the following sintering process: 1) Degrease at 580-650℃ by heating at 1-3℃ / min and holding for 1-3 hours; 2) Continue heating to 1050~1100℃ and hold for 1~2 hours to carry out densification sintering; 3) Then cool down to 950~1000℃ and hold for 2~4 hours to control grain size; After sintering, cool to room temperature at 2~5℃ / min.

[0017] Optionally, the polarization process in step S6 includes the following staged coupling polarization steps: 1) Apply an electric field polarization of 3.0~4.0 kV / mm at 50~70℃ for 10~20 minutes; 2) Heat to 80~100℃ and apply an electric field of 2.5~3.0 kV / mm for 15~30 minutes to polarize; 3) Further heat to 110~130℃, and apply an electric field polarization of 1.5~2.5 kV / mm for 5~15 minutes; It was then cooled to room temperature at a rate of 2-5 °C / min under the influence of an electric field.

[0018] Optionally, in step S3, the amount of lithium borosilicate glass additive added is 0.3~0.8wt%, and the ball milling conditions are 180~250 rpm and 3~6 hours.

[0019] Optionally, the pressing pressure in step S4 is 5~30 MPa.

[0020] Optionally, in step S1, the preheating temperature is 850~900℃ and the holding time is 2~4 hours.

[0021] Optionally, in step S1, the ball milling speed is 250~300 rpm and the time is 12~20 hours.

[0022] Optionally, in step S2, the ball milling speed is 200~300 rpm and the time is 8~12 hours.

[0023] Optionally, the amount of adhesive added is 3 to 8 wt%.

[0024] Optionally, in step S3, the ball milling speed for dispersing the lithium boron aluminum silicon glass additive is 150~250 rpm, and the time is 2~6 hours.

[0025] Optionally, the thickness of the green blank in step S4 is 0.8~1.5 mm.

[0026] Optionally, the molding process in step S4 is unidirectional compression molding.

[0027] This application provides the application of the above-mentioned high-density lead-free piezoelectric ceramic material, or the lead-free piezoelectric ceramic material obtained by the above preparation method, in piezoelectric actuators, sensors, or ultrasonic transducers.

[0028] The beneficial effects of this application include, but are not limited to: 1. According to the high-density lead-free piezoelectric ceramics, their preparation method, and applications of this application, by introducing a specific composition of Li2O-B2O3-SiO2-Al2O3 quaternary oxide glass additive, softening occurs during sintering, which can promote the rearrangement of ceramic particles and rapid closure of pores; simultaneously, in the subsequent cooling stage, the glass phase re-solidifies and distributes at the grain boundaries, playing a filling and pinning role on the grain boundaries, inhibiting pore regeneration and abnormal grain growth; further combined with an optimized sintering process, a balance is achieved between densification and grain control, ultimately obtaining a microstructure with relatively high density and significantly reduced internal porosity, providing a structural basis for the stable performance of piezoelectric properties.

[0029] 2. According to the high-density lead-free piezoelectric ceramics, their preparation methods, and applications of this application, the enrichment of the glass phase in the grain boundary region can effectively reduce the grain boundary migration rate, thereby enhancing the stability of the grain boundary structure. At the same time, MnO2, as a defect modulator, introduces an appropriate amount of controlled defects (such as oxygen vacancies) into the lattice, which can regulate the internal electric field distribution and suppress the disordered migration of defects at high temperatures. The synergistic effect of the two makes the grain boundary structure and electric domain structure of the material remain stable during temperature changes, thereby significantly improving the temperature stability and long-term service reliability of the piezoelectric ceramics and reducing the degree of performance degradation with temperature fluctuations.

[0030] 3. Based on the high-density lead-free piezoelectric ceramics, their preparation method, and applications described in this application, by introducing (Bi... 0.5 Na 0.5 TiO3 components are incorporated into the KNN matrix in a solid solution form, creating localized polarization regions with relaxation characteristics in the material. This lowers the domain flipping energy barrier, making the domains more easily oriented under an applied electric field. Simultaneously, a staged coupling polarization process is used to gradually achieve domain nucleation, expansion, and stabilization under different temperatures and electric field strengths. This avoids the problems of insufficient polarization or local over-polarization in traditional single polarization methods, thereby improving the polarization efficiency of the material and allowing the piezoelectric properties to be more fully released.

[0031] 4. Based on the high-density lead-free piezoelectric ceramics, their preparation methods, and applications of this application, through the synergistic design of MnO2 defect control, glass phase grain boundary control, and optimized sintering process and staged polarization process, a unified optimization of the multi-scale structure of "lattice-grain boundary-electric domain" is achieved at the microscopic level. Among them, the defect concentration is controlled within a range that is conducive to domain wall movement without excessive pinning, the grain boundary structure is stabilized and densified, and the polarization path is matched with the energy barrier distribution inside the material. Thus, while improving piezoelectric performance, dielectric loss and performance degradation are effectively reduced, and finally, a lead-free piezoelectric ceramic material with high density, high stability, and good piezoelectric response is obtained. Attached Figure Description

[0032] 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 scanning electron microscope (SEM) image of the piezoelectric ceramic involved in Embodiment 1 of this application. Detailed Implementation

[0033] 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.

[0034] The present application solution will be described below through specific embodiments.

[0035] Example 1 This embodiment provides a high-density lead-free piezoelectric ceramic and its preparation method. The chemical composition of this piezoelectric ceramic is 0.99 (K). 0.48 Na 0.46 Ag 0.06 (Nb) 0.90 Ta 0.06 Sb 0.02 Zr 0.02 O3-0.01(Bi 0.5 Na 0.5 TiO3 was used, and 0.5 wt% of lithium boron aluminum silicon glass additive (Li2O–B2O3–SiO2–Al2O3 quaternary oxide system) and 0.2 mol% of MnO2 were introduced as defect control agents during the sintering process.

[0036] 1) Raw materials and ingredients The following raw materials were selected: potassium carbonate (K2CO3), sodium carbonate (Na2CO3), silver oxide (Ag2O), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), antimony trioxide (Sb2O3), zirconium dioxide (ZrO2), bismuth oxide (Bi2O3), titanium dioxide (TiO2), manganese oxide (MnO2), and pre-prepared lithium boron aluminum silicon glass additives.

[0037] Weigh each raw material according to the above stoichiometric ratio, and prepare the batch based on 100g of matrix powder. The amount of K2CO3 and Na2CO3 is increased by 3mol% on the basis of the theoretical amount to compensate for the loss of alkali metal volatilization during high-temperature sintering.

[0038] 2) Preparation of matrix powder Weighed K2CO3, Na2CO3, Ag2O, Nb2O5, Ta2O5, Sb2O3 and ZrO2 were added to a planetary ball mill. Zirconia balls were used as the grinding media (ball-to-material ratio 5:1), and anhydrous ethanol was added as the dispersion medium. The mixture was ball-milled at 280 rpm for 16 hours.

[0039] After ball milling, the slurry was dried in an 85℃ forced-air drying oven for 12 hours to obtain a mixed powder. The dried powder was placed in a covered alumina crucible and pre-fired in a box-type resistance furnace at a heating rate of 4℃ / min, heated to 880℃ and held for 3 hours to obtain a preliminary KNN-based solid solution powder.

[0040] 3) Secondary ball milling After pulverizing the pre-calcined material and passing it through a 100-mesh sieve, add Bi₂O₃, TiO₂, and Na₂CO₃ (the amounts added should be based on (Bi...). 0.5 Na 0.5 (Calculated by TiO3 accounting for 1 mol% of the total system molar fraction), and after pre-calcination, 0.2 mol% (based on the total molar number of ABO3 matrix) of MnO2 was added as a defect control agent, and the mixture was ball-milled again at 250 rpm for 10 hours in ethanol medium.

[0041] After ball milling, the powder is dried and passed through a 100-mesh sieve to obtain composite powder.

[0042] 4) Preparation of lithium boron aluminum silicon glass additives Analytical grade Li₂CO₃, H₃BO₃, SiO₂, and Al₂O₃ were weighed and thoroughly mixed in a molar ratio of 25:35:20:20. The mixture was placed in a platinum crucible and heated to 1150℃ in a resistance furnace at a rate of 5℃ / min, holding for 1.5 hours to completely melt and form a homogeneous glass melt. The melt was then rapidly poured into deionized water for quenching to obtain glass fragments. After drying at 80℃ for 12 hours, the fragments were pulverized using a planetary ball mill, controlling the particle size to be 0.5~2μm (D).50 (Approximately 1 μm), to obtain lithium boron aluminum silicon glass additive. The prepared lithium boron aluminum silicon glass additive has a glass transition temperature of 450~500℃ and a softening temperature of 550~600℃.

[0043] 5) Glass phase introduction and granulation Add 0.5 wt% of lithium boron aluminum silicon glass additive to the above composite powder, and ball mill at 200 rpm for 4 hours in ethanol medium to uniformly disperse the glass phase on the powder surface. After ball milling, dry and pass through a 100-mesh sieve to obtain piezoelectric powder.

[0044] Subsequently, a 6 wt% polyvinyl alcohol aqueous solution was added as a binder, and after being mixed evenly, it was granulated manually through a 100-mesh sieve.

[0045] 6) Molding The material is 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 1.0~1.2mm.

[0046] 7) Sintering The green body was placed in a covered alumina crucible and sintered in air atmosphere as follows: 7.1) Degreasing stage The temperature was increased to 600℃ at a rate of 2℃ / min and held for 2 hours to remove the organic binder. 7.2) First stage densification The temperature was increased to 1070℃ at a rate of 5℃ / min and held for 1.5 hours to soften the glass phase and promote rapid densification. 7.3) Second-stage grain control The temperature was lowered to 980℃ and held for 3 hours to suppress abnormal grain growth and stabilize the grain boundary structure. After sintering, the sample was cooled to room temperature at 3℃ / min to obtain a high-density ceramic sample.

[0047] 8) Electrode preparation and coupling 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 750°C for 15 minutes to form conductive electrodes.

[0048] The sample was then placed in silicone oil for staged coupling polarization treatment: 8.1) Low-temperature high-field polarization stage A 3.5 kV / mm electric field was applied for polarization at 60℃ for 15 minutes; 8.2) Mid-temperature stable polarization stage Heat to 90℃ and apply an electric field of 2.8kV / mm for 20 minutes to polarize; 8.3) High Temperature and Low Field Control Stage The temperature was further increased to 120°C, and an electric field of 2.0 kV / mm was applied for polarization for 10 minutes; After polarization, the material is cooled to room temperature at a rate of 3°C / min under the influence of an electric field to obtain the high-density lead-free piezoelectric ceramic material, such as... Figure 1 As shown.

[0049] Comparative Example 1 The composition and preparation method of this comparative example are basically the same as those of Example 1, except that lithium boron aluminum silicon glass additives were not added.

[0050] Comparative Example 2 The composition and preparation method of this comparative example are basically the same as those of Example 1, except that no MnO2 defect modifier was added.

[0051] Comparative Example 3 The preparation method of this comparative example is basically the same as that of Example 1, except that it does not contain (Bi) in its chemical composition. 0.5 Na 0.5 TiO3 component (x=0).

[0052] Comparative Example 4 The comparative example has the same composition and pretreatment process as Example 1. The difference is that the sintering process does not use a staged sintering process, but a single-step sintering process is used, that is, the temperature is raised to 1080°C and held for 2 hours, and then directly cooled to room temperature. All other conditions remain the same.

[0053] Comparative Example 5 The comparative example has the same composition and sintering process as Example 1, except that: instead of a staged coupling polarization process, a single polarization method is used for polarization treatment. The polarization is carried out at 120°C with an electric field of 3.0 kV / mm for 20 minutes and then cooled to room temperature.

[0054] Comparative Example 6 This comparative example is the same as Example 1, except that the lithium boron aluminum silicon glass additive is replaced with a Li2O-B2O3-SiO2 ternary glass that does not contain Al2O3, while the other conditions are the same.

[0055] Comparative Example 7 This comparative example is the same as Example 1, except that the lithium boron aluminum silicon glass additive is added simultaneously with the matrix raw material during the first ball milling stage, instead of being added after pre-firing. All other conditions are the same.

[0056] Comparative Example 8 This comparative example is the same as Example 1, except that x = 0.03.

[0057] Comparative Example 9 This comparative example is the same as Example 1, except that the densification temperature is 1020°C, and the other conditions are the same.

[0058] Comparative Example 10 This comparative example is the same as Example 1, except that the densification temperature is 1120°C, and the other conditions are the same.

[0059] 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.

[0060] The test items include the following: To characterize the degree of densification of the material, the relative density (in %) of the samples was measured using the Archimedes method. The sintered samples were immersed in deionized water, and their dry weight, suspended weight, and saturated weight were measured. The bulk density was calculated and compared with the theoretical density to obtain the relative density. This parameter reflects the internal porosity and densification level of the material; a higher relative density indicates better material densification, thus verifying the effect of glass additives in promoting sintering densification.

[0061] To characterize the piezoelectric properties of the material, the piezoelectric constant d was measured using a quasi-static piezoelectric constant tester. 33 (Unit: pC / N). This parameter reflects the material's electrical response under mechanical stress, d 33 A higher value indicates better piezoelectric performance.

[0062] To characterize the energy loss of the material, a precision LCR meter was used to measure the dielectric loss tanδ (dimensionless) at room temperature and 1 kHz. This parameter reflects the degree of energy dissipation of the material during the application of an electric field; a lower tanδ indicates less energy loss.

[0063] 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 conductive defects and electrical insulation properties of a material; the lower the leakage current density, the lower the defect concentration.

[0064] To evaluate the temperature stability of the material, the piezoelectric constant d of the sample was measured before and after heat treatment. 33 And calculate d 33 Retention rate (unit: %). Specifically: The sample was incubated at 150℃ for 2 hours, cooled to room temperature, and then the retention rate was measured again. 33 This value is compared with the initial value. This parameter reflects the performance stability of the material under high temperature conditions; a higher retention rate indicates better temperature stability.

[0065] Table 1. Performance test results of the examples and comparative products.

[0066] Table 1 (continued)

[0067] As shown in Table 1, Example 1 of this application exhibits significant advantages in all performance indicators. The relative density of Example 1 reaches 97.6%, which is significantly higher than that of Comparative Example 1 (94.8%), Comparative Example 4 (95.6%), and Comparative Example 9 (93.8%). This indicates that by introducing lithium borosilicate glass additives, this application can effectively promote particle rearrangement and porosity elimination during sintering, thereby significantly improving the material density.

[0068] Regarding piezoelectric properties, d in Example 1 33 The ratio reached 305 pC / N, significantly better than Comparative Example 3 (245 pC / N), Comparative Example 5 (275 pC / N), and Comparative Example 10 (255 pC / N). Notably, Comparative Example 3 did not introduce (Bi) 0.5 Na 0.5 The TiO3 composition results in a lack of relaxation structure regulation, reduced domain flipping ability, and thus a significant decrease in piezoelectric performance. Comparative Example 5, lacking a staged polarization process, suffers from insufficient domain orientation, also leading to d... 33 The performance decreased. Therefore, it is evident that this application, through the introduction of BNT components and a staged coupling polarization process, plays a crucial role in reducing the domain switching energy barrier and optimizing the domain structure, thereby significantly improving piezoelectric performance.

[0069] Regarding loss and defect control, Example 1 exhibits a dielectric loss tanδ of 0.017 and a leakage current density of 2.2E-7 A / cm². 2 These values ​​were the lowest among all groups. In contrast, Comparative Example 2, without the addition of MnO2, showed a significant increase in tanδ to 0.038 and a leakage current density to 1.4E-6 A / cm². 2 This indicates that internal defects in the material (especially oxygen vacancies) have not been effectively controlled, leading to increased conductivity loss. Therefore, MnO2, as a defect modifier in this application, plays a significant role in inhibiting oxygen vacancy migration and reducing leakage current and energy loss.

[0070] Regarding temperature stability, d in Example 1 33The retention rate reached 91%, significantly better than Comparative Example 2 (74%), Comparative Example 3 (79%), and Comparative Example 9 (72%). Among them, Comparative Example 2, lacking defect control, experienced accelerated defect migration at high temperatures, leading to significant performance degradation; Comparative Example 3, due to the absence of BNT components, exhibited poor material structural stability; and Comparative Example 9, due to insufficient sintering temperature, had low density and unstable structure, thus demonstrating poor temperature stability. These results indicate that this application effectively improves the material's performance retention capability under high-temperature environments.

[0071] Furthermore, after Comparative Examples 6 and 7 changed the glass additive system or its addition method, their relative density and d 33 All showed a decrease, indicating that the composition and introduction method of glass additives have a significant impact on material properties; Comparative Example 8 showed a decrease in piezoelectric properties and stability due to the BNT content deviating from the optimal range, further demonstrating that the distribution ratio of each group in this application has a synergistic optimization effect.

[0072] In summary, this application achieves grain boundary liquid phase control by introducing lithium boron aluminum silicon glass additives, achieves defect control through MnO2, and combines (Bi... 0.5 Na 0.5 The TiO3 component relaxation structure design and the staged sintering and staged polarization process make the material significantly superior to the comparative material in terms of density, piezoelectric properties, loss control and temperature stability, thus effectively solving the problems of low density, many defects and poor performance stability in the existing technology.

[0073] 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-density lead-free piezoelectric ceramic, characterized in that, The general chemical formula of the lead-free piezoelectric ceramic is (1-x)(K a Na b Ag c (Nb) p Ta q Sb r Zr s )O3-x(Bi 0.5 Na 0.5 TiO3, where 0.45≤a≤0.50, 0.44≤b≤0.48, 0.04≤c≤0.08, and a+b+c=1; 0.88≤p≤0.92, 0.04≤q≤0.08, 0.01≤r≤0.03, 0.01≤s≤0.03, and p+q+r+s=1; 0.005≤x≤0.02; In the lead-free piezoelectric ceramic, 0.2~1.0wt% of lithium boron aluminum silicon glass additive and 0.1~0.5mol% of MnO2 are introduced as defect control agents. The lithium boron aluminum silicon glass additive is a quaternary oxide system of Li2O-B2O3-SiO2-Al2O3.

2. The high-density lead-free piezoelectric ceramic according to claim 1, characterized in that, a=0.48, b=0.46, c=0.06, p=0.90, q=0.06, r=0.02, s=0.02, x=0.

01.

3. The high-density lead-free piezoelectric ceramic according to claim 1, characterized in that, The molar ratio of each component in the lithium boron aluminum silicon glass additive is Li2O:B2O3:SiO2:Al2O3=(20~30):(30~40):(15~25):(15~25).

4. The high-density lead-free piezoelectric ceramic according to claim 3, characterized in that, The lithium boron aluminum silicon glass additive has a glass transition temperature of 450~500℃, a softening temperature of 550~600℃, and a particle size of 0.5~2μm.

5. The method for preparing high-density lead-free piezoelectric ceramics according to any one of claims 1 to 4, 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, which is then pre-calcined to obtain a pre-calcined powder; S2. After pulverizing the pre-calcined powder, add (Bi) 0.5 Na 0.5 The raw materials required for TiO3 composition and MnO2 undergo secondary ball milling. S3. Add lithium boron aluminum silicon glass additive to the obtained powder and continue ball milling to disperse it evenly; S4. Add binder, granulate, sieve and press to form green body; S5. The green blank is sintered to obtain a sintered body; S6. After preparing electrodes from the sintered body, perform staged coupling polarization treatment to obtain the lead-free piezoelectric ceramic material.

6. The method for preparing high-density lead-free piezoelectric ceramics according to claim 5, characterized in that, Step S5 includes the following sintering process: 1) Degrease at 580-650℃ by heating at 1-3℃ / min and holding for 1-3 hours; 2) Continue heating to 1050~1100℃ and hold for 1~2 hours; 3) Then cool down to 950~1000℃ and keep warm for 2~4 hours; After sintering, cool to room temperature at 2~5℃ / min.

7. The method for preparing high-density lead-free piezoelectric ceramics according to claim 5, characterized in that, The polarization process in step S6 includes the following staged coupling polarization steps: 1) Apply an electric field polarization of 3.0~4.0 kV / mm at 50~70℃ for 10~20 minutes; 2) Heat to 80~100℃ and apply an electric field of 2.5~3.0 kV / mm for 15~30 minutes to polarize; 3) Further heat to 110~130℃, and apply an electric field polarization of 1.5~2.5 kV / mm for 5~15 minutes; It was then cooled to room temperature at a rate of 2-5 °C / min under the influence of an electric field.

8. The method for preparing high-density lead-free piezoelectric ceramics according to claim 5, characterized in that, In step S3, the amount of lithium boron aluminum silicon glass additive added is 0.3~0.8wt%, and the ball milling conditions are 180~250 rpm and 3~6 hours.

9. The method for preparing high-density lead-free piezoelectric ceramics according to claim 5, characterized in that, The pressing pressure in step S4 is 5~30 MPa.

10. The application of the high-density lead-free piezoelectric ceramic material as described in any one of claims 1 to 4, or the lead-free piezoelectric ceramic material obtained by the preparation method as described in any one of claims 5 to 9, in piezoelectric actuators, sensors, or ultrasonic transducers.

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