Preparation method of low sintering temperature lead-free piezoelectric ceramic system

Abstract

The present invention belongs to the field of piezoelectric technology and discloses a method for preparing a low sintering temperature lead-free piezoelectric ceramic system. The specific steps are as follows: Step 1: Raw material ratio and precise weighing Chemical formula design: According to the chemical formula 0.7Bi 1.01 Fe x O3‑0.3BaTiO3, in which the stoichiometric ratio of iron is designed within the range of 0.79≤x≤0.88. By precisely controlling the stoichiometric ratio, two pre-sintering processes combined with oxygen protection sintering process, Fe 3+ Reduction and oxygen vacancy formation construct a stable defect dipole structure, form a built-in electric field, significantly reduce the domain deflection energy barrier, and increase the material's electrostrain by 129% at 45kV / cm; cold isostatic pressing and bidirectional pressurization forming processes synergistically improve the density of the green body, and combined with submicron powder low-temperature sintering technology, the traditional process sintering temperature is reduced to 840°C, greatly reducing energy consumption and lattice distortion risks, and showing high strain sensitivity, low dielectric loss and long life in the field of lead-free piezoelectric ceramics.

Description

Technical Field

[0001] The present invention belongs to the field of piezoelectric technology, and in particular relates to a method for preparing a low-sintering-temperature lead-free piezoelectric ceramic system. Background Art

[0002] Piezoelectric ceramic materials are a type of functional ceramics with a unique piezoelectric effect. Their core properties stem from the electrical response of the crystal structure under mechanical stress. When squeezed or stretched by external force, the internal charge distribution undergoes a directionally shifted shift to form a potential difference (positive piezoelectric effect). Conversely, when an alternating electric field is applied, mechanical deformation occurs (inverse piezoelectric effect). This bidirectional energy conversion characteristic distinguishes it from ordinary ceramic materials. Lead-based piezoelectric ceramics represented by lead zirconate titanate (PZT) dominate the market, with a piezoelectric coefficient of up to 300-600. They play a key role in modern scientific and technological fields such as sensors, transducers, and micro-actuators.

[0003] Piezoelectric ceramic materials can realize the mutual conversion of electrical energy and mechanical energy, and have been widely used in the fields of sensors and actuators. Piezoelectric actuators with good performance need to be realized through lamination. Laminated piezoelectric materials usually have two characteristics: one is excellent electrostrain performance, and the other is a suitable low-temperature sintering process that can be co-fired with low-cost and low-melting-point electrodes such as silver and copper. BiFeO3-BaTiO3-based piezoelectric ceramics have attracted widespread attention due to their high Curie temperature (~450℃) and relatively excellent electrostrain (~0.3%). However, this ceramic system has a long history in the preparation process due to Bi 3+ Volatilization and Fe 3+ The change in valence of ions leads to low insulation resistance, which makes it difficult to use in actual products. Improving its electrostrain at low sintering temperature is an important part of its application in actual products. Electrostrain mainly causes the device to deform the material through an external electric field during actual use. The sintering temperature of piezoelectric ceramic drivers generally used in products exceeds 1000°C and cannot be matched with other low-melting-point electrodes, which makes it difficult to use in piezoelectric drivers, so it needs to be improved. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a lead-free piezoelectric ceramic system with a low sintering temperature, so as to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solution: a method for preparing a low sintering temperature lead-free piezoelectric ceramic system, the specific steps of which are as follows:

[0006] Step 1: Raw material ratio and accurate weighing

[0007] Chemical formula design: According to the chemical formula 0.7Bi 1.01Fe x O3-0.3BaTiO3, wherein the stoichiometric ratio of iron element is in the range of 0.79≤x≤0.88 for formulation design;

[0008] Raw material selection and weighing: Select raw material powders (BaCO3, TiO2, Bi2O3, Fe2O3) with a purity of ≥99.9%, and vacuum dry them at 120°C for 4 hours before use to remove adsorbed moisture. Accurately weigh each component according to the stoichiometric ratio, with the error controlled within plus or minus 0.1% to ensure the uniformity of the material composition;

[0009] Step 2: Wet ball milling mixing process

[0010] Ball milling parameters: The weighed raw material powder was mixed with deionized water or anhydrous ethanol at a mass ratio of 1:1. Zirconia balls were added as grinding media with a ball-to-material ratio of 5:1. Wet ball milling was performed in a ball mill at 300 rpm for 12 hours to avoid powder stratification.

[0011] Drying and sieving: The ball-milled slurry is vacuum filtered to remove the liquid medium, and then vacuum dried at 80°C for 24 hours to obtain a uniformly mixed dry precursor powder. The powder is then passed through a 200-mesh nylon sieve to remove hard agglomerated particles and obtain a mixed powder with good fluidity.

[0012] Step 3: Pre-firing process optimization

[0013] The volatile impurities in the raw materials, such as CO2 and H2O, are eliminated through two pre-calcinations, and the solid-phase reaction is promoted to form the main crystal phase of the perovskite phase. The dry powder is placed in an alumina crucible for the first pre-calcination and heated to 800°C in a box furnace at a heating rate of 5°C per minute. The temperature is kept for 4 hours and then naturally cooled to room temperature. During the second pre-calcination, the powder after the first pre-calcination is ball-milled again for 2 hours to break up agglomerates, and then pre-calcined again at the same temperature (800°C) for 4 hours to finally obtain a high-purity pre-calcined ceramic powder.

[0014] Step 4: Secondary ball milling and granulation

[0015] Powder refinement: The pre-fired ceramic powder is subjected to a secondary wet ball milling process for 8 hours to further reduce the powder particle size to submicron level, about 0.5 microns, to improve sintering activity;

[0016] Binder addition and granulation: After drying, a 7% by mass fraction of polyvinyl alcohol (PVA) binder is added to the powder. The mixture is prepared into a granulated powder with a uniform particle size of 50 to 100 microns and good fluidity through a spray granulator to facilitate subsequent molding.

[0017] Step 5: Tablet forming process

[0018] Molding parameters: The granulated powder was loaded into a stainless steel mold and pressed on a uniaxial tablet press at a pressure of 150 MPa for 10 seconds to form a circular green body with a thickness of 1.1 mm and a diameter of 12 mm. To reduce density gradients, a bidirectional pressure mode was used during the pressing process, and the pressure was maintained for 30 seconds during the holding stage.

[0019] Step 6: Sintering process control

[0020] Sintering temperature and time: Place the green body on an alumina backing plate and heat it in air at a heating rate of 3°C per minute to a target temperature of 820°C to 900°C. Hold the temperature for 2 to 3 hours to promote grain densification and grain boundary migration.

[0021] Oxygen vacancy suppression: During the sintering process, the formation of oxygen vacancies is reduced by controlling the heating rate and holding time to avoid Fe 3+ The negative impact of valence changes on the electrical properties of materials;

[0022] Step 7: Cooling and post-processing

[0023] Cooling procedure: After sintering, the sample is rapidly cooled to 800°C at a rate of 10°C per minute. The sample is then removed from the furnace and naturally cooled to room temperature in air. This can reduce microcracks caused by thermal stress while preserving the defect dipole structure in the lattice.

[0024] Surface treatment: The sintered ceramic sheet is double-sided polished to remove the surface oxide layer, and finally a finished ceramic material with a thickness of 1.0 mm and a surface roughness of less than 0.1 micron is obtained.

[0025] Preferably, in step seven, the microstructure and chemical properties of the ceramic material are analyzed by systematic characterization means, and the surface morphology and internal crystal structure of the material are observed respectively by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); X-ray diffraction (XRD) is used to verify that the main crystal phase is a perovskite structure and no impurity phase is generated; Raman spectroscopy (Raman) is used to analyze the chemical bonding state to confirm that the lattice vibration characteristics match the designed composition.

[0026] Preferably, the Bi2O3 in step 1 needs to be stored separately in a dry nitrogen cabinet to prevent weighing errors caused by moisture absorption.

[0027] Preferably, the molar ratio of the bismuth element in step 1 is set to 1.01. Preliminary experiments have shown that an excess of 1% can effectively offset the Bi 3+ of volatility.

[0028] Preferably, the ball mill in step 2 is set to rotate at 300 rpm, and operates in forward and reverse directions alternately, switching directions every 30 minutes.

[0029] Preferably, the finished ceramic material in step seven needs to be moisture-proof packaged, and the polished ceramic sheet is placed in a transparent aluminum-plastic bag filled with dry nitrogen, and a humidity indicator card and a deoxidizer are placed in the bag. After hot pressing and sealing, it is stored in a constant temperature and humidity chamber at a temperature of 25±3°C and a humidity of ≤10% RH to prevent the Bi2O3 component from reacting with ambient water vapor and causing the piezoelectric performance to decay.

[0030] Preferably, in step 5, the green body is heated to 600° C. at a rate of 1° C. / min in an air atmosphere and kept at that temperature for 2 hours to completely remove the PVA binder, with the residual carbon content being ≤0.05%.

[0031] Preferably, the sintering process in step 6 adopts an oxygen protection process, and after the temperature is raised to 800°C, a low flow rate of oxygen is continuously introduced into the furnace to maintain an oxidizing atmosphere and suppress Fe 3+ ions are reduced to Fe 2+ , reducing the generation of oxygen vacancies inside the material and avoiding the degradation of electrical performance caused by lattice distortion.

[0032] Preferably, after the press molding in step five, cold isostatic pressing is performed, the green body is sealed in a flexible mold, and a pressure of 200-300 MPa is applied in a hydraulic device and maintained for 10-15 minutes to make the internal structure of the green body denser, eliminate the density unevenness caused by uniaxial pressing, and provide a high-density green body foundation for subsequent sintering.

[0033] The beneficial effects of the present invention are as follows:

[0034] By precisely controlling the stoichiometry, two pre-sintering processes combined with oxygen protection sintering process, Fe 3+ Reduction and oxygen vacancy formation construct a stable defect dipole structure, form a built-in electric field, significantly reduce the domain deflection energy barrier, and increase the electrostrain of the material by 129% at 45kV / cm; cold isostatic pressing and bidirectional pressurization forming processes synergistically improve the density of the green body, and combined with submicron powder low-temperature sintering technology, the traditional process sintering temperature is reduced to 840℃, greatly reducing energy consumption and lattice distortion risks. It exhibits high strain sensitivity, low dielectric loss and long life in the field of lead-free piezoelectric ceramics, and is suitable for high-end electronic devices such as precision sensors and micro-actuators. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a multi-scale structural characterization map of the present invention;

[0036] Figure 2 This is a diagram showing the effect of the present invention on electrostrain. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] like Figure 1 As shown, the embodiment of the present invention provides a method for preparing a low sintering temperature lead-free piezoelectric ceramic system, and the specific steps are as follows:

[0039] Step 1: Raw material ratio and accurate weighing

[0040] Chemical formula design: According to the chemical formula 0.7Bi 1.01 Fe x O3-0.3BaTiO3, wherein the stoichiometric ratio of iron element is in the range of 0.79≤x≤0.88 for formulation design;

[0041] Raw material selection and weighing: Select raw material powders (BaCO3, TiO2, Bi2O3, Fe2O3) with a purity of ≥99.9%, and vacuum dry them at 120°C for 4 hours before use to remove adsorbed moisture. Accurately weigh each component according to the stoichiometric ratio, with the error controlled within plus or minus 0.1% to ensure the uniformity of the material composition;

[0042] Step 2: Wet ball milling mixing process

[0043] Ball milling parameters: The weighed raw material powder was mixed with deionized water or anhydrous ethanol at a mass ratio of 1:1. Zirconia balls were added as grinding media with a ball-to-material ratio of 5:1. Wet ball milling was performed in a ball mill at 300 rpm for 12 hours to avoid powder stratification.

[0044] Drying and sieving: The ball-milled slurry is vacuum filtered to remove the liquid medium, and then vacuum dried at 80°C for 24 hours to obtain a uniformly mixed dry precursor powder. The powder is then passed through a 200-mesh nylon sieve to remove hard agglomerated particles and obtain a mixed powder with good fluidity.

[0045] Step 3: Pre-firing process optimization

[0046] The volatile impurities in the raw materials, such as CO2 and H2O, are eliminated through two pre-calcinations, and the solid-phase reaction is promoted to form the main crystal phase of the perovskite phase. The dry powder is placed in an alumina crucible for the first pre-calcination and heated to 800°C in a box furnace at a heating rate of 5°C per minute. The temperature is kept for 4 hours and then naturally cooled to room temperature. During the second pre-calcination, the powder after the first pre-calcination is ball-milled again for 2 hours to break up agglomerates, and then pre-calcined again at the same temperature (800°C) for 4 hours to finally obtain a high-purity pre-calcined ceramic powder.

[0047] Step 4: Secondary ball milling and granulation

[0048] Powder refinement: The pre-fired ceramic powder is subjected to a secondary wet ball milling process for 8 hours to further reduce the powder particle size to submicron level, about 0.5 microns, to improve sintering activity;

[0049] Binder addition and granulation: After drying, a 7% by mass fraction of polyvinyl alcohol (PVA) binder is added to the powder. The mixture is prepared into a granulated powder with a uniform particle size of 50 to 100 microns and good fluidity through a spray granulator to facilitate subsequent molding.

[0050] Step 5: Tablet forming process

[0051] Molding parameters: The granulated powder was loaded into a stainless steel mold and pressed on a uniaxial tablet press at a pressure of 150 MPa for 10 seconds to form a circular green body with a thickness of 1.1 mm and a diameter of 12 mm. To reduce density gradients, a bidirectional pressure mode was used during the pressing process, and the pressure was maintained for 30 seconds during the holding stage.

[0052] Step 6: Sintering process control

[0053] Sintering temperature and time: Place the green body on an alumina backing plate and heat it in air at a heating rate of 3°C per minute to a target temperature of 820°C to 900°C. Hold the temperature for 2 to 3 hours to promote grain densification and grain boundary migration.

[0054] Oxygen vacancy suppression: During the sintering process, the formation of oxygen vacancies is reduced by controlling the heating rate and holding time to avoid Fe 3+ The negative impact of valence changes on the electrical properties of materials;

[0055] Step 7: Cooling and post-processing

[0056] Cooling procedure: After sintering, the sample is rapidly cooled to 800°C at a rate of 10°C per minute. The sample is then removed from the furnace and naturally cooled to room temperature in air. This can reduce microcracks caused by thermal stress while preserving the defect dipole structure in the lattice.

[0057] Surface treatment: The sintered ceramic sheet is double-sided polished to remove the surface oxide layer, and finally a finished ceramic material with a thickness of 1.0 mm and a surface roughness of less than 0.1 micron is obtained.

[0058] By design 0.7Bi 1.01 Fe xO3-0.3BaTiO3 chemical formula, using excess 1% bismuth element to compensate for sintering volatilization, through two pre-sintering, two-way pressure tableting, oxygen protection sintering and rapid cooling process, combined with cold isostatic pressing treatment to improve the density of the green body, by suppressing Fe 3+ Reduction and oxygen vacancy formation construct defect dipoles, and the built-in electric field formed by aging is used to reduce the domain deflection energy, so that the sintering temperature can be reduced from 1000℃ to 800℃ while maintaining high-purity perovskite phase and submicron grains, achieving high electrostrain performance under low driving electric field.

[0059] Among them, in step seven, the microstructure and chemical properties of the ceramic material are analyzed through systematic characterization methods. The surface morphology and internal crystal structure of the material are observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively; X-ray diffraction (XRD) is used to verify that the main crystal phase is a perovskite structure and no impurity phase is generated; combined with Raman spectroscopy (Raman), the chemical bonding state is analyzed to confirm that the lattice vibration characteristics match the designed composition.

[0060] Electron microscope, transmission electron microscope, X-ray diffraction and Raman spectrum of ceramic materials are as shown in the attached instructions. Figure 1 As shown in the figure, ad is the SEM spectrum of the BFx-BT component, eh is the TEM morphology of the BFx-BT component, i is the XRD spectrum of the BFx-BT component, and j is the Raman spectrum of the BFx-BT component. The principle diagram of the influence of electrostrain, the actual measured PE, SE curves and the built-in electric field changes constructed by the defect dipole are shown in the appendix of the specification. Figure 2 shown.

[0061] In step 1, Bi2O3 must be stored separately in a dry nitrogen cabinet to prevent weighing errors caused by moisture absorption.

[0062] Storing Bi2O3 separately in a dry nitrogen cabinet can effectively block the hygroscopic effect of ambient moisture, avoid quality fluctuations of raw materials caused by moisture absorption, and ensure weighing accuracy and chemical metrological stability of subsequent formulas.

[0063] The molar ratio of bismuth in step 1 is set to 1.01. Preliminary experiments have shown that an excess of 1% can effectively offset the Bi 3+ of volatility.

[0064] By setting the bismuth molar ratio to 1.01, the 1% excess compensation mechanism verified by the pre-experimental verification can accurately offset the Bi 3+ The volatilization loss is reduced, the theoretical consistency of the chemical composition of the final product is maintained, the stability and repeatability of the piezoelectric performance of the material are improved, and the final stoichiometry is ensured to be close to the theoretical value.

[0065] In step 2, the ball mill speed was set to 300 rpm, and the ball mill was operated alternately in forward and reverse directions, with the direction being switched every 30 minutes.

[0066] By setting the ball mill to a 300rpm alternating forward and reverse operation mode, the grinding direction is periodically changed to break the powder agglomeration tendency, enhance the uniformity of particle dispersion, avoid the local uneven mixing caused by unidirectional rotation, and improve the composition uniformity of the precursor powder.

[0067] Among them, the finished ceramic material in step seven needs to be moisture-proof packaged. The polished ceramic piece is placed in a transparent aluminum-plastic bag filled with dry nitrogen. A humidity indicator card and a deoxidizer are placed in the bag. After hot pressing and sealing, it is stored in a constant temperature and humidity chamber at a temperature of 25±3°C and a humidity of ≤10% RH to prevent the Bi2O3 component from reacting with ambient water vapor and causing the piezoelectric performance to deteriorate.

[0068] By placing the polished ceramic sheet in a transparent aluminum-plastic bag filled with dry nitrogen, combined with multiple protections of deoxidizer and humidity indicator card, the ceramic sheet is effectively isolated from the erosion of environmental moisture and oxygen, the deliquescence and oxidative degradation of the Bi2O3 component are inhibited, and the stability of the material's piezoelectric properties is maintained for a long time.

[0069] In step 5, the green body is heated to 600° C. at a rate of 1° C. / min in an air atmosphere and kept at this temperature for 2 hours to completely remove the PVA binder, with the residual carbon content being ≤0.05%.

[0070] By adopting a step-by-step debinding process of slowly heating the temperature to 600°C at 1°C / min and keeping it at that temperature for 2 hours, the PVA adhesive is fully pyrolyzed and the carbon residue is completely removed, avoiding the residual carbon from triggering a reduction reaction during the high-temperature sintering stage, thereby ensuring the electrical insulation performance and dielectric properties of the ceramic.

[0071] Among them, the sintering process in step 6 adopts the oxygen protection process. After the temperature is raised to 800℃, low-flow oxygen is continuously introduced into the furnace to maintain an oxidizing atmosphere and inhibit Fe 3+ ions are reduced to Fe 2+ , reducing the generation of oxygen vacancies inside the material and avoiding the degradation of electrical performance caused by lattice distortion.

[0072] The oxygen protection sintering process suppresses Fe 3+ Fe 2+ The reduction reaction and oxygen vacancy formation reduce the risk of lattice distortion, improve the dielectric constant and piezoelectric coefficient of the material, and reduce the negative impact of leakage current on performance.

[0073] Among them, after the pressing and forming in step 5, cold isostatic pressing is performed, the green body is sealed in a flexible mold, and a pressure of 200-300 MPa is applied in a hydraulic device and maintained for 10-15 minutes to make the internal structure of the green body denser, eliminate the density unevenness caused by uniaxial pressing, and provide a high-density green body foundation for subsequent sintering.

[0074] Cold isostatic pressing eliminates the density gradient and internal porosity generated by uniaxial pressing through isotropic high-pressure densification, allowing the green body to achieve a higher density, allowing the grains to grow uniformly during the sintering stage, and improving the mechanical strength and piezoelectric response consistency of the final ceramic.

[0075] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0076] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low sintering temperature lead-free piezoelectric ceramic system, characterized in that: The specific steps are as follows: Step 1: Raw material ratio and accurate weighing Chemical formula design: According to the chemical formula 0.7Bi 1.01 Fe x O3-0.3BaTiO3, wherein the stoichiometric ratio of iron element is in the range of 0.79≤x≤0.88 for formulation design; Raw material selection and weighing: Select raw material powders of BaCO3, TiO2, Bi2O3, and Fe2O3 with a purity of ≥99.9%. Vacuum dry them at 120°C for 4 hours before use to remove adsorbed moisture. Accurately weigh each component according to the stoichiometric ratio, with an error controlled within plus or minus 0.001% to ensure the uniformity of the material composition. Step 2: Wet ball milling mixing process Ball milling parameters: The weighed raw material powder was mixed with deionized water or anhydrous ethanol at a mass ratio of 1:

1. Zirconia balls were added as grinding media with a ball-to-material ratio of 5:

1. Wet ball milling was performed in a ball mill at 360 rpm for 12 hours to achieve uniform powder. Drying and sieving: The ball-milled slurry is vacuum filtered to remove the liquid medium, and then vacuum dried at 80°C for 24 hours to obtain a uniformly mixed dry precursor powder. The powder is then passed through an 80-mesh nylon sieve to remove hard agglomerated particles and obtain a mixed powder with good fluidity. Step 3: Pre-firing process optimization The process involves pre-firing the raw materials twice to eliminate volatile impurities such as CO2 and H2O, and promoting solid-phase reaction to form a perovskite phase. For the first pre-firing, the dry powder is placed in an alumina crucible and heated to 800°C in a box furnace at a heating rate of 5°C per minute. The mixture is kept warm for 4 hours and then naturally cooled to room temperature. During the second pre-firing, the pre-firing powder is ball-milled for 2 hours to break up agglomerates, and then pre-firing is performed again at 800°C for 4 hours to obtain a high-purity pre-firing ceramic powder. Step 4: Secondary ball milling and granulation Powder refinement: The pre-fired ceramic powder is subjected to a secondary wet ball milling process for 8 hours to further reduce the powder particle size to 0.5 microns and improve sintering activity; Binder addition and granulation: After drying, a 7% by mass fraction of polyvinyl alcohol (PVA) binder is added to the powder. The mixture is prepared into a granulated powder with a uniform particle size of 50 to 100 microns and good fluidity through a spray granulator to facilitate subsequent molding. Step 5: Tablet forming process Molding parameters: The granulated powder was loaded into a stainless steel mold and pressed on a uniaxial tablet press at a pressure of 150 MPa for 10 seconds to form a circular green body with a thickness of 1.1 mm and a diameter of 12 mm. To reduce density gradients, a bidirectional pressure mode was used during the pressing process, and the pressure was maintained for 30 seconds during the holding stage. Step 6: Sintering process control Sintering temperature and time: Place the green body on an alumina pad and heat it to a target temperature of 820°C to 900°C in an air atmosphere at a heating rate of 3°C per minute. Keep it warm for 2 to 3 hours to promote grain densification and grain boundary migration. The sintering process adopts an oxygen protection process. After heating to 800°C, a low flow of oxygen is continuously introduced into the furnace to maintain an oxidizing atmosphere and inhibit Fe 3+ ions are reduced to Fe 2+ , reducing the generation of oxygen vacancies inside the material and avoiding the degradation of electrical performance caused by lattice distortion; Oxygen vacancy suppression: During the sintering process, the formation of oxygen vacancies is reduced by controlling the heating rate and holding time to avoid Fe 3+ The negative impact of valence changes on the electrical properties of materials; Step 7: Cooling and post-processing Cooling procedure: After sintering, the sample is rapidly cooled to 800°C at a rate of 10°C per minute. The sample is then removed from the furnace and naturally cooled to room temperature in air. This can reduce microcracks caused by thermal stress while preserving the defect dipole structure in the lattice. Surface treatment: The sintered ceramic sheet is double-sided polished to remove the surface oxide layer, and finally a finished ceramic material with a thickness of 1.0 mm and a surface roughness of less than 0.1 micron is obtained.

2. The method for preparing a low sintering temperature lead-free piezoelectric ceramic system according to claim 1, wherein: The Bi2O3 described in step 1 needs to be stored separately in a dry nitrogen cabinet to prevent weighing errors caused by moisture absorption.

3. The method for preparing a low sintering temperature lead-free piezoelectric ceramic system according to claim 1, wherein: The molar ratio of bismuth in step 1 is set to 1.

01. Preliminary experiments have shown that an excess of 1% can effectively offset the Bi 3+ of volatility.

4. The method for preparing a low sintering temperature lead-free piezoelectric ceramic system according to claim 1, wherein: The ball mill in step 2 was operated alternately in forward and reverse directions, switching directions every 30 minutes.

5. The method for preparing a low sintering temperature lead-free piezoelectric ceramic system according to claim 1, wherein: The finished ceramic material described in step 7 needs to be moisture-proof packaged. The polished ceramic piece is placed in a transparent aluminum-plastic bag filled with dry nitrogen. A humidity indicator card and deoxidizer are placed in the bag. After hot pressing and sealing, it is stored in a constant temperature and humidity chamber at a temperature of 25±3°C and a humidity of ≤10% RH to prevent the Bi2O3 component from reacting with ambient water vapor and causing degradation of the piezoelectric performance.

6. The method for preparing a low sintering temperature lead-free piezoelectric ceramic system according to claim 1, wherein: In step 5, the green body is heated to 600° C. at a rate of 1° C. / min in an air atmosphere and kept at this temperature for 2 hours to completely remove the PVA binder, with a residual carbon content of ≤0.05%.

7. The method for preparing a low sintering temperature lead-free piezoelectric ceramic system according to claim 1, wherein: After the tableting described in step 5, cold isostatic pressing is performed, the green body is sealed in a flexible mold, and a pressure of 200-300 MPa is applied in a hydraulic device and maintained for 10-15 minutes to make the internal structure of the green body denser, eliminate the density unevenness caused by uniaxial pressing, and provide a high-density green body foundation for subsequent sintering.

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