A bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material, a preparation method and application thereof

Abstract

The application discloses a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material and a preparation method and application thereof, and relates to the technical field of functional materials. The chemical formula of the bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material is (0.7-x)BiFeO3-0.3BaTiO3-xBiAlO3, wherein x=0.005-0.015, and x represents a molar fraction. The application introduces BiAlO3 into BF-BT lead-free piezoelectric ceramic through a third component solid solution mode, synthesizes a brand-new multi-component solid solution high-temperature lead-free piezoelectric ceramic material by adopting a traditional solid-phase reaction method, constructs a morphotropic phase boundary, and improves the piezoelectric performance and Curie temperature of the lead-free piezoelectric ceramic material.

Description

Technical Field

[0001] This invention relates to the field of lead-free piezoelectric ceramics preparation technology, specifically to a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material with high piezoelectric properties and high Curie temperature, as well as its preparation method and application. Background Technology

[0002] High-temperature piezoelectric ceramics, as an extremely important electronic ceramic material, are widely used in high-performance high-temperature sensing devices such as AC circuit voltage transformers, sensors, and precision positioners, as well as other electromechanical equipment. However, due to widespread environmental problems and strict regulations imposed by governments worldwide on lead-containing materials, coupled with the high mass content of lead tetroxide (approximately 60%) in PZT-based ceramics, and the increasingly stringent requirements for the operating temperature of piezoelectric ceramics across various industries, the development of environmentally friendly high-temperature piezoelectric materials is imperative.

[0003] BiFeO3 piezoelectric ceramics, with their high Curie temperature and large remanent polarization, have attracted widespread attention from researchers and are a highly promising high-temperature lead-free piezoelectric ceramic system. However, BiFeO3-based piezoelectric ceramics have a narrow sintering temperature range, making it difficult to synthesize a single crystalline phase and prone to Bi formation. 25 FeO 39 The BiFeO3 ceramic samples contain impurity phases such as Bi2Fe4O9. Furthermore, BiFeO3 ceramic samples exhibit poor ferroelectric properties, very low piezoelectric constants, and are difficult to polarize. These problems significantly hinder the application of BiFeO3 piezoelectric ceramics. However, with the discovery of quasi-isomorphic phase boundary regions (MPB) in BiFeO3-BaTiO3 (BF-BT), its piezoelectric properties have been greatly improved, making BF-BT-based lead-free piezoelectric ceramics a new and popular research direction.

[0004] As research into BF-BT piezoelectric ceramics deepens, researchers have discovered that although BF-BT-based piezoelectric ceramics possess the MPB region, their piezoelectric performance is still lower than that of traditional lead-based ceramics. Furthermore, high Curie temperature and high piezoelectric performance are often mutually exclusive, severely limiting the realization of their piezoelectric potential.

[0005] Chinese invention patent application CN121285248A discloses a high-temperature lead-free piezoelectric ceramic material, its preparation method, and a piezoelectric ceramic device. This method obtains a perovskite phase structure (1-x)(0.7BiFeO3-0.3BaTiO3)-x(Ba(Zr) 0.5 Ti 0.5 (O3) ceramic powder; wherein, 0.02≤x≤0.06. This technology introduces Zr... 4+ The ionic radius is as high as 0.72 Å, significantly larger than that of the original B-site ion. Large-radius Zr 4+Upon entering the crystal lattice, the oxygen octahedron expands, compressing the spontaneous displacement space of B-site ions and weakening the spontaneous polarization intensity of the lattice. Macroscopically, this manifests as a difficulty in achieving a significant leap in the quasi-static piezoelectric constant. Therefore, although this piezoelectric ceramic material can replace traditional lead-based piezoelectric ceramics in applications under high temperature and low electric field conditions, its piezoelectric performance remains relatively low and its high-temperature polarization thermal stability is relatively insufficient.

[0006] Chinese invention patent application CN117585998A discloses a lead-free piezoelectric ceramic material and its preparation method. This method yields 0.7BiFeO3-0.3BaTiO3-x(Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O3 ceramic powder was used to obtain ceramic samples with high piezoelectric properties, but the Curie temperature decreased significantly. Although BCZT has a high piezoelectric constant, its Curie temperature is extremely low (typically only around 90 °C). Large-scale solid dissolution of this low-Curie-temperature component causes the overall system's Curie temperature to rapidly drop towards lower temperatures, and its high tolerance factor means that incorporation will also affect the Curie temperature. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, this invention provides a high-temperature lead-free piezoelectric ceramic material and its preparation method. The piezoelectric properties are improved by introducing a quasi-isomorphic phase boundary through the introduction of the tertiary component BiAlO3. Furthermore, the low tolerance factor of BiAlO3 enhances the Curie temperature, and the small ionic radius of the tertiary component BiAlO3 contributes to the improved piezoelectric performance. 3+ The incorporation of [a substance] will not cause the oxygen octahedron to expand in volume, thereby squeezing the spontaneous displacement space of B-site ions and weakening the spontaneous polarization intensity of the lattice.

[0008] Another objective of this invention is to provide the application of bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic materials in the fabrication of piezoelectric ceramic components.

[0009] The technical problem to be solved by this invention is achieved through the following technical solution:

[0010] A bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material with the chemical formula (0.7-x)BiFeO3-0.3BaTiO3-xBiAlO 3， Where x = 0.005~0.015, x represents the mole fraction.

[0011] The preparation method of the bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material includes the following steps:

[0012] (1) Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2 and Al2O3 according to their chemical formulas and prepare them into powder;

[0013] (2) The powder is granulated and formed into an embryo;

[0014] (3) Perform degumming treatment on the embryo;

[0015] (4) The preform after debinding treatment is sintered to obtain ceramic material;

[0016] (5) The ceramic material is subjected to silver plating polarization treatment to obtain bismuth ferrite-barium titanate based high temperature lead-free piezoelectric ceramic material.

[0017] To further achieve the purpose of the present invention, preferably, in step (1), when preparing the powder, the weighed raw materials are subjected to ball milling, drying, pre-calcination and ball milling in sequence, and the resulting slurry is taken out and dried into powder.

[0018] More preferably, in the two ball milling processes, the rotation speed of the ball mill is 280-320 r / min, and the ball milling time is 10-12 h;

[0019] During the pre-firing process, the temperature is controlled at 730-750 ℃, and the holding time is 3-4 h.

[0020] Preferably, in step (2), the preparation of the embryo involves adding a binder to the obtained powder, stirring and granulating it, sieving it after granulation, and then pressing it into a sheet on a hydraulic press; the shape of the embryo is a round sheet.

[0021] Preferably, the adhesive is a polyvinyl alcohol aqueous solution with a mass concentration of 5%-10% and the amount of polyvinyl alcohol aqueous solution added is 10-12% of the total mass of the powder; the sieve size for the sieving process is 80-100 mesh; the diameter of the disc-shaped preform is 10-11 mm and the thickness is 0.9 mm to 1.1 mm.

[0022] Preferably, in step (3), the glue removal process involves slowly heating the room temperature to 550-600 ℃ and holding it at that temperature for 20-30 minutes, followed by natural cooling to room temperature.

[0023] Preferably, in step (4), the sintering method is buried firing;

[0024] In step (5), the process of silvering the ceramic material involves polishing the upper and lower surfaces of the ceramic material, ultrasonically cleaning and drying it, coating the upper and lower surfaces of the dried ceramic sheet with a layer of silver paste with a diameter of 6-8 mm, drying it, and then performing a silver firing process to obtain a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material.

[0025] Preferably, the sintering involves burying the disc blank with pre-fired powder in the same proportion as the blank and then sintering it, controlling the sintering temperature at 960 ℃~980 ℃ and the holding time at 3-4 h.

[0026] The drying is carried out in an oven; the silver burning process is carried out in a muffle furnace.

[0027] This invention protects the application of the bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material in the fabrication of piezoelectric ceramic elements, including its application in next-generation miniaturized, lightweight, highly reliable, and high-temperature stable piezoelectric device systems.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] 1) All components of this invention form a pure perovskite solid solution; with the increase of BiAlO3 content, the system undergoes a structural transformation from a trigonal phase to a tetragonal phase; the system is located in a quasi-isomorphic phase boundary region where R and T phases coexist, and the multidirectional selectivity of the polarization vector provides a structural basis for excellent piezoelectric properties.

[0030] 2) This invention is due to the small radius Al 3+ The substitution-induced lattice distortion caused a steady increase in the Curie temperature of the system, rising from 478 °C in Comparative Example 1 to approximately 498 °C, demonstrating excellent high-temperature polarization stability. The components located within the MPB region, due to the combined effects of phase boundary effects and high density, exhibited ferroelectric and piezoelectric properties in the example samples, achieving the following remanent polarization intensity P r = 27.3 μC / cm 2 piezoelectric constant d 33 = 165 pC / N; Maximum electrostriction S max = 0.21%. d 33 * = 530 pm / V.

[0031] 3) By introducing BiAlO3 as a third component to construct a ternary solid solution, this invention successfully achieved a significant improvement in the electromechanical conversion efficiency of 0.7BiFeO3-0.3BaTiO3 ceramics while maintaining high-temperature characteristics, providing important support for the development of high-performance high-temperature lead-free piezoelectric actuators.

[0032] 4) The ceramic obtained by this invention has a smaller grain size and lower porosity, which greatly improves the electrical properties of the ceramic and helps to improve both piezoelectric properties and Curie temperature. Attached Figure Description

[0033] Figure 1The X-ray diffraction patterns of the samples obtained in Comparative Example 1, Example 1, Example 2, and Example 3 are shown, along with a magnified view of the (110) diffraction peak in the XRD pattern.

[0034] Figure 2 The images shown are SEM micrographs of the thermally etched surfaces and grain size distribution diagrams of Comparative Example 1, Example 1, Example 2, and Example 3 of this invention.

[0035] Figure 3 The figures show the ferroelectric performance test results for Comparative Example 1, Example 1, Example 2, and Example 3 of this invention.

[0036] Figure 4 The dielectric temperature spectra of Comparative Example 1, Example 1, Example 2, and Example 3 of the present invention at different frequencies are shown.

[0037] Figure 5 The figures show the test results of the piezoelectric constant and electromechanical coupling coefficient of Comparative Example 1, Example 1, Example 2, and Example 3 of this invention.

[0038] Figure 6 The figures are unipolar electrostrain curves of Comparative Example 1, Example 1, Example 2, and Example 3 of the present invention.

[0039] Figure 7 The inverse piezoelectric constant test diagrams are for Comparative Example 1, Example 1, Example 2, and Example 3 of this invention. Specific implementation methods

[0040] To better understand this invention, the objectives, technical solutions, and effects of this invention are explained below, and further description is provided in conjunction with the accompanying drawings and specific embodiments. However, the implementation of this invention is not limited thereto. The described embodiments are some, but not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0041] This invention incorporates a tertiary component, BiAlO3, into a 0.7BiFeO3-0.3BaTiO3 ceramic material. The introduction of BiAlO3 refines the grain size (see...). Figure 2 This is beneficial for improving the density of ceramics and subsequent electrical properties; moreover, by adjusting the ratio of trigonal and tetragonal phases in 0.7BF-0.3BT ceramics, a quasi-isomorphic phase boundary is constructed where the trigonal and tetragonal phases coexist. The trigonal / tetragonal phases have similar energies, are easily polarized and rotated, and have easily movable domain walls, which reduces the difficulty of domain flipping in ceramic samples and improves piezoelectric properties. Figure 1 (Table 1 demonstrates the changes in phase structure). Furthermore, constructing a quasi-isomorphic phase boundary where trigonal and tetragonal phases coexist is beneficial for improving the ferroelectric properties of the material. The remanent polarization intensity of this invention increases from P...r = 18.5 μC / cm 2 Can be upgraded to P r = 27 μC / cm 2 .

[0042] Curie temperature is often strongly negatively correlated with tolerance factor. A smaller tolerance factor makes the oxygen octahedron more prone to tilting, leading to greater instability of the ferroelectric distortion. This means a higher temperature is required to transform it into the paraelectric phase, resulting in a higher Curie temperature Ti. c Higher. This invention utilizes BiAlO3, which has a smaller tolerance factor than 0.7BF-0.3BT, to increase the Curie temperature T of the material. c The tolerance factor can be calculated from the ionic radius using a formula.

[0043] Therefore, this invention provides a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material with the chemical formula (0.7-x)BiFeO3-0.3BaTiO3-xBiAlO 3， Where x = 0.005~0.015, x represents the mole fraction.

[0044] The preparation method of this bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material includes the following steps:

[0045] (1) Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2 and Al2O3 according to their chemical formulas and prepare them into powder;

[0046] (2) The powder is granulated and formed into an embryo;

[0047] (3) Perform degumming treatment on the embryo;

[0048] (4) The preform after debinding treatment is sintered to obtain ceramic material;

[0049] (5) The ceramic material is subjected to silver plating polarization treatment to obtain bismuth ferrite-barium titanate based high temperature lead-free piezoelectric ceramic material.

[0050] In step (1), preparing the raw material into powder is a basic practice in this field. The weighed raw material is subjected to ball milling, drying, pre-calcination, and ball milling in sequence. The resulting slurry is then dried into powder. Preferably, in the two ball milling processes, the ball mill speed is 280-320 r / min and the ball milling time is 10-12 h; preferably, the pre-calcination temperature is controlled at 730-750 ℃ ​​and the holding time is controlled at 3-4 h.

[0051] In step (2), the preparation of the preform generally involves adding a binder to the obtained powder, stirring and granulating it, then sieving it, and finally pressing it into sheets on a hydraulic press. The preferred shape of the preform is a disc, but other shapes are also possible, including regular polygons or shapes specific to particular applications. The preferred binder is a polyvinyl alcohol aqueous solution, with a preferred mass concentration of 5%-10%, and the preferred amount of polyvinyl alcohol added is 10-12% of the total powder mass. The preferred sieve size for sieving in this step is 80-100 mesh. The preferred diameter of the disc-shaped preform is 10-11 mm, and the preferred thickness is 0.9 mm to 1.1 mm. Both the diameter and thickness can be adjusted according to application requirements.

[0052] In step (3), the glue removal process is also a common process in the field. The preferred glue removal process of this invention is to slowly heat the room temperature to 550-600 ℃ and keep it at that temperature for 20-30 min, and then let it cool naturally to room temperature.

[0053] In step (4), the preferred sintering method is buried firing; the buried firing is to bury the disc blank with pre-fired powder in the same proportion as the blank and then sinter it, controlling the sintering temperature to be 960 ℃~980 ℃ and the holding time to be 3-4 h.

[0054] In step (5), the silver plating polarization treatment involves first polishing the upper and lower surfaces of the ceramic material, then ultrasonically cleaning and drying it. A layer of silver paste with a diameter of 6-8 mm is then coated on the upper and lower surfaces of the dried ceramic sheet. After drying, the material is then subjected to silver burning treatment to obtain a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material.

[0055] The performance characterization methods for the ceramics obtained in the examples and comparative examples include:

[0056] (1) Phase structure characterization: The crystal structure and phase structure of (0.7-x)BF-0.3BT-xBAO ceramics were characterized by X-ray diffraction (XRD) using a Cu target Ka-ray, with a test angle range of 20°-80° and a scanning speed of 2° / min. To accurately characterize the phase composition and crystallographic features of the material, the sintered ceramic block was thoroughly ground into a uniform powder state using a mortar before testing to eliminate possible preferred orientation effects.

[0057] (2) Microscopic Morphology Characterization: The microscopic morphology and porosity of the samples were analyzed using a scanning electron microscope (SEM). The working principle of this instrument is to use a focused electron beam to scan the sample surface, acquiring surface morphology information through the emitted secondary electrons or backscattered electron signals. To obtain clear images and prevent charge accumulation under electron beam irradiation, representative samples were first selected and successively polished with 400-2000 grit sandpaper, then polished to a mirror finish with diamond polishing paste, and finally ultrasonically cleaned with ethanol for 10-15 minutes to remove surface impurities. The cleaned samples were then dried in an oven. Due to the poor conductivity of the samples in this study, a gold film with a thickness of approximately 10-20 nm was sprayed onto the sample surface using an ion sputtering instrument before the experiment to enhance conductivity.

[0058] (3) Electrical and Mechanical Performance Testing: Using a ferroelectric testing instrument, the hysteresis loop (PE loop) of the sample was obtained at room temperature, 1 Hz frequency, and within an electric field range of 10-50 kV / cm. This hysteresis loop is the core criterion for evaluating ferroelectric properties. Its physical essence lies in the fact that the spontaneous polarization of the electric domains within the ceramic can switch with the direction of the external field, resulting in a nonlinear response of the polarization intensity to the electric field, thus forming a typical closed curve of a two-valued function. By analyzing the hysteresis loop, the key ferroelectric performance parameters of the ceramic can be obtained. This test is based on the Sawyer-Tower test circuit, which is the mainstream standard method in the industry.

[0059] Dielectric-temperature characterization was performed in a resistance furnace. At C p In -D operating mode, the impedance analyzer monitors samples placed in a 700℃ resistance furnace. The system is programmed to automatically sample every 2℃ during the heating process, simultaneously acquiring capacitance and dielectric loss. The raw data of capacitance fluctuations with temperature can be used to calculate the corresponding dielectric constant curve. The dielectric constant is calculated according to the IEC 60672 standard and reflects the dipole response and conductivity contribution within the material.

[0060] Polarization was performed using an oil bath piezoelectric polarization device (HYJH-8 / 10kV). The specific operating steps are as follows: Place the ceramic sample in high-temperature silicone oil at 120 ℃, calculate the required polarization voltage based on the sample thickness, and maintain it for 15 min to complete the polarization.

[0061] Using quasi-static d 33 The measuring instrument was used to test the polarized ceramic sample at room temperature to obtain its piezoelectric constant d. 33(Unit: pC / N). Before testing, the sample needs to be polarized to orient the originally randomly oriented internal domains along the electric field direction. The quasi-static piezoelectric constant is measured using the Berlincourt method (following ANSI / IEEE Std 176-1987 standard) to evaluate piezoelectric performance and thermal stability. This method involves applying a dynamic force of known frequency and amplitude to the ceramic sheet and measuring the induced charge generated. This method directly measures the piezoelectric effect and is the most intuitive indicator recognized by industry and academia.

[0062] The maximum electrostricted strain value was obtained by measuring the unipolar electrostricted strain curve using a ferroelectric tester under conditions of room temperature, an electric field of 50 kV / cm, and a test frequency of 1 Hz. The electrostricted strain curve measurement employed a linkage system of a ferroelectric analyzer and a laser displacement sensor. The normalized strain constant was calculated based on the definition of the large-signal piezoelectric constant, which is a key indicator for evaluating the performance of piezoelectric actuators under actual operating field strength.

[0063] Comparative Example 1

[0064] (1) Prepare chemical reagents Bi2O3 (99.9%), Fe2O3 (99.9%), BaCO3 (99.9%), and TiO2 (99.9%).

[0065] (2) Weigh the chemical reagents in step 1 according to the chemical formula 0.7BF-0.3BT on a high-precision analytical balance, and then place the powder mixture in a polytetrafluoroethylene ball mill jar, use anhydrous ethanol as the dispersion medium, and ball mill for 10 h at a speed of 280 r / min to ensure that the chemical reagents are fully mixed.

[0066] (3) The highly mixed slurry was dried in a high-temperature furnace. The dried powder was placed in an alumina crucible, covered with a crucible lid, and then placed in a muffle furnace for pre-firing. The pre-firing temperature was set at 750 ℃ ​​and held for 3 h. After pre-firing, the powder was placed in a ball mill jar and ball-milled in a planetary ball mill at a speed of 280 r / min for 10 h. The slurry was then removed and dried into powder.

[0067] (4) Add a 5 wt% polyvinyl alcohol aqueous solution binder to the obtained powder, the amount of which is 10% of the total powder mass. Stir and granulate, then pass the mixture through 80 mesh and 120 mesh sieves and press it into tablets. The molding pressure is set to 200 MPa. The powder is molded into round blanks with a diameter of 10 mm and a thickness of 1.1 mm.

[0068] (5) The disc preform samples were debinded in a muffle furnace. The debinding process involved slowly heating the sample from room temperature to 600℃ and holding it for 20 minutes. After holding, the sample was allowed to cool naturally to room temperature. Then, the debinded disc preform samples were placed in a muffle furnace for sintering. The disc preforms were buried and covered with pre-fired powder of the same proportion as the disc preforms to effectively prevent element volatilization. The sintering temperature was set to 980℃, held for 3 hours, and then allowed to cool naturally to room temperature.

[0069] (6) Polish the upper and lower surfaces of the obtained ceramic sample. Then, clean the polished ceramic in an ultrasonic cleaner for 10 min and dry it in a drying oven. After drying, coat the upper and lower surfaces of the ceramic sheet with a layer of silver paste. Finally, place the ceramic in a muffle furnace for silver firing. The temperature of the muffle furnace is set to 600℃ at a heating rate of 5℃ / min, hold for 30 min, and then cool naturally to obtain 0.7BF-0.3BT ceramic material.

[0070] The prepared 0.7BF-0.3BT ceramic material samples were tested in the following manner.

[0071] (1) The 0.7BF-0.3BT ceramic material samples were tested using XRD and SEM. The test results are shown in the figure. Figure 1 The ceramic exhibits a pure perovskite structure. The refined XRD data of Comparative Example 1 are shown in Table 1, and they agree well with the standard cards for the trigonal phase of BF and the tetragonal phase of BT, indicating that the sample possesses a coexisting trigonal and tetragonal two-phase structure with a high degree of fit confidence. Meanwhile, the SEM test results are shown in... Figure 2 The ceramic sample has a dense surface structure with no obvious visible pores or defects.

[0072] (2) The hysteresis loop of the ceramic sample was tested by ferroelectric analysis, and the remanent polarization intensity was determined by the hysteresis loop. The test results are shown in […]. Figure 3 The remanent polarization intensity P of the ceramic sample was obtained. r P r = 18.5 μC / cm 2 .

[0073] (3) The dielectric properties of the ceramic samples were measured using a high-temperature dielectric temperature spectrometer. The test results are shown in [Figure number missing]. Figure 4 The Curie temperature at which the ceramic sample was obtained was 478 °C.

[0074] (4) Quasi-static d 33 The measuring instrument was used to test the polarized ceramic sample at room temperature. The test results are shown below. Figure 5 The piezoelectric constant d of the 0.7BF-0.3BT ceramic sample was obtained. 33 = 119 pC / N; k p= 0.23.

[0075] (5) The unipolar electrostriction curve of the ceramic sample was measured using a ferroelectric tester under the conditions of room temperature, 50 kV / cm electric field, and 1 Hz test frequency. The test results are shown in […]. Figure 6 , Figure 7 The maximum electroinduced strain value S was obtained. max = 0.144% and inverse piezoelectric constant d 33 * = 355 pm / V.

[0076] Example 1

[0077] (1) Prepare chemical reagents Bi2O3 (99.9%), Fe2O3 (99.9%), BaCO3 (99.9%), TiO2 (99.9%) and Al2O3 (99%).

[0078] (2) Weigh the chemical reagents in step 1 according to the chemical formula 0.695BF-0.3BT-0.005BAO on a high-precision analytical balance, then place the powder mixture in a polytetrafluoroethylene ball mill jar, use anhydrous ethanol as the dispersion medium, and ball mill for 11 h at a speed of 290 r / min to ensure that the chemical reagents are fully mixed.

[0079] (3) The highly mixed slurry was dried in a high-temperature furnace. The dried powder was placed in an alumina crucible, covered with a crucible lid, and placed in a muffle furnace for pre-firing. The pre-firing temperature was set at 740 ℃ and held for 4 h. After pre-firing, the powder was placed in a ball mill jar and ball-milled in a planetary ball mill at a speed of 290 r / min for 11 h. The slurry was then removed and dried into powder.

[0080] (4) Add a 5 wt% polyvinyl alcohol aqueous solution binder to the obtained ceramic powder. The amount of polyvinyl alcohol aqueous solution added is 12% of the total powder mass. Stir and granulate, then pass through 80 mesh and 120 mesh sieves respectively and press into sheets. The molding pressure is set to 200 MPa. The powder is molded into round blanks with a diameter of 10 mm and a thickness of 1.1 mm.

[0081] (5) The sample disc preforms were debinded in a muffle furnace. The debinding process involved slowly heating the sample disc preforms from room temperature to 580℃ and holding them at that temperature for 30 minutes. After holding, the temperature was allowed to cool naturally to room temperature. Then, the debinded sample disc preforms were placed in a muffle furnace for sintering. The disc preforms were buried and covered with pre-fired powder of the same proportion as the disc preforms to effectively prevent element volatilization. The sintering temperature was set to 970℃, and the temperature was held for 4 hours, followed by natural cooling to room temperature.

[0082] (6) Polish the upper and lower surfaces of the obtained ceramic sample. Then, clean the polished ceramic in an ultrasonic cleaner for 10 min and dry it in a drying oven. After drying, coat the upper and lower surfaces of the ceramic sheet with a layer of silver paste. Finally, place the ceramic in a muffle furnace for silver firing. The temperature of the muffle furnace is set to 600℃ at a heating rate of 5℃ / min, hold for 30 min, and then cool naturally to obtain ceramic material that meets the requirements for electrical testing and engineering applications.

[0083] The performance of the 0.69BF-0.3BT-0.005BAO ceramic material prepared by the method of this embodiment was tested using the following methods.

[0084] (1) The ceramic sample was tested using XRD and SEM. The test results are shown in the figure. Figure 1 The ceramic exhibits a pure perovskite structure, and no obvious impurity peaks were observed in the XRD, proving that BAO was successfully introduced into the BF-BT lattice. The diffraction peak at (110) shows a splitting of the trigonal phase characteristic peak, which is weaker compared to Comparative Example 1, indicating that the ceramic sample is transforming from a trigonal to a tetragonal phase. The refined XRD data of Example 1 further confirms the coexistence of the trigonal and tetragonal phases, as shown in Table 1. Table 1 shows the phase structure composition and some parameters of the unit cell obtained by fitting the original XRD data using GASA II software. The fitting results in Table 1 are in good agreement with the standard cards for the trigonal phase of BF and the tetragonal phase of BT, indicating a high degree of reliability (R). wp <10, GOF<2), and the cell volume decreases, indicating that small-radius Al 3+ Successful integration. The results showed a 70% trigonal phase and a 30% tetragonal phase, indicating a trend towards a shift from trigonal to tetragonal phases compared to Comparative Example 1. Meanwhile, the SEM test results are shown below. Figure 2 After introducing 0.005 BAO into the matrix, it was found that the grain size of the ceramic sample decreased, the sample surface was very dense, and there were no obvious visible pores or defects.

[0085] (2) The hysteresis loop of the ceramic sample was tested by ferroelectric analysis, and the remanent polarization intensity was determined by the hysteresis loop. The test results are shown in […]. Figure 3 The remanent polarization intensity P of the ceramic sample was obtained. r = 23.8 μC / cm 2 This indicates that the introduction of BAO facilitates more complete flipping of domain walls under the influence of an electric field.

[0086] (3) The dielectric behavior of the ceramic sample was measured using a high-temperature dielectric temperature spectrometer. The test results are shown in […]. Figure 4It was found that introducing 0.005 BAO increased the Curie temperature of BF-BT ceramic materials to 487 °C. This is because the tolerance factor of BAO (approximately 0.81) is lower than that of BF (approximately 0.84) and BT (approximately 0.97). Curie temperature is generally inversely proportional to the tolerance factor; a lower tolerance factor leads to stronger stability of the long-range ferroelectric order, resulting in increased phase transition heat energy required for the transition from the ferroelectric to the paraelectric phase, manifested as an increase in Curie temperature. The increase in Curie temperature is beneficial for stabilizing and maintaining piezoelectric properties at high temperatures.

[0087] (4) Quasi-static d 33 The measuring instrument was used to test the polarized ceramic sample at room temperature. The maximum piezoelectric constant d of the ceramic sample was obtained. 33 = 143 pC / N; k p = 0.273, which is an improvement compared to Comparative Example 1, indicating that the introduction of BAO improved the piezoelectric properties of the original 0.7BF-0.3BT piezoelectric ceramic material. The test results are shown in […]. Figure 5 .

[0088] (5) The unipolar electrostriction curves of the BF-BT-0.005BAO ceramic sample were measured using a ferroelectric testing instrument under the conditions of room temperature, 50 kV / cm electric field, and 1 Hz test frequency. The test results are shown in […]. Figure 6 , Figure 7 The maximum electroinduced strain value S was obtained. max =0.201% and inverse piezoelectric constant d 33 * = 487 pm / V, an improvement over Comparative Example 1.

[0089] Example 2

[0090] (1) Prepare chemical reagents Bi2O3 (99.9%), Fe2O3 (99.9%), BaCO3 (99.9%), TiO2 (99.9%) and Al2O3 (99%).

[0091] (2) Weigh the chemical reagents in step 1 according to the chemical formula 0.69BF-0.3BT-0.01BAO on a high-precision analytical balance, and then place the powder mixture in a polytetrafluoroethylene ball mill jar, use anhydrous ethanol as the dispersion medium, and ball mill for 12 h at a speed of 300 r / min to ensure that the chemical reagents are fully mixed.

[0092] (3) The highly mixed slurry was dried in a high-temperature furnace. The dried powder was placed in an alumina crucible, covered with a crucible lid, and then placed in a muffle furnace for pre-firing. The pre-firing temperature was set at 730 ℃ and held for 4 h. After pre-firing, the powder was placed in a ball mill jar and ball-milled in a planetary ball mill at a speed of 300 r / min for 12 h. The slurry was then removed and dried into powder.

[0093] (4) Add a 10 wt% polyvinyl alcohol aqueous solution binder to the obtained powder. The amount of polyvinyl alcohol aqueous solution added is 10% of the total powder mass. Stir and granulate, then pass through 80-mesh and 120-mesh sieves respectively and press into tablets. The molding pressure is set to 200 MPa. The powder is molded into round blanks with a diameter of 10 mm and a thickness of 0.9 mm.

[0094] (5) The sample wafer preform was subjected to debinding treatment in a muffle furnace. The debinding treatment involved slowly heating from room temperature to 550 ℃ and holding at that temperature for 30 min. After holding, it was allowed to cool naturally to room temperature. Then, the debinded wafer preform was placed in a muffle furnace for sintering. The wafer preform was covered with the corresponding powder by embedding it in the furnace, which effectively prevented the volatilization of elements. The sintering temperature was set to 960 ℃, and the holding time was 4 h, followed by natural cooling to room temperature.

[0095] (6) Polish the upper and lower surfaces of the ceramic material. Then, clean the polished ceramic in an ultrasonic cleaner for 10 min and dry it in a drying oven. After drying, coat the upper and lower surfaces of the ceramic sheet with a layer of silver paste. Finally, place the ceramic in a muffle furnace for silver firing. The temperature of the muffle furnace is set to 600℃ at a heating rate of 5℃ / min, hold for 30 min, and then cool naturally to obtain a ceramic material that meets the requirements for electrical testing and engineering applications.

[0096] The performance of the 0.69BF-0.3BT-0.01BAO ceramic material prepared by the method of this embodiment was tested using the following methods.

[0097] (1) The ceramic samples were tested using XRD and SEM. The test results are shown in the figure. Figure 1 Similar to Example 1, from Figure 1 It can be proven that BAO was successfully introduced into the BF-BT lattice. The ceramic exhibits a pure perovskite structure with both trigonal and tetragonal phases coexisting. The characteristic peak splitting at (110) is further weakened, indicating that the ceramic sample continues to transform from the trigonal to the tetragonal phase. The refined XRD data of Example 2 are shown in Table 1, which also matches the standard cards for the trigonal phase of BF and the tetragonal phase of BT. The fitting confidence is very high, and the cell volume is further reduced, indicating that more small-radius Al 3+Successful integration resulted in a trigonal phase composition of 58% and a tetragonal phase composition of 42%, continuing the trend of transitioning from trigonal to tetragonal phases. Furthermore, the similar proportions of trigonal and tetragonal phases at this stage represent a classic quasi-isomorphic phase boundary region, which is beneficial for improving piezoelectric performance. Meanwhile, SEM test results are shown below. Figure 2 After introducing 0.01% BAO into the matrix, the grain size of the ceramic sample was further reduced, and the sample surface was very dense with no obvious visible pores or defects.

[0098] (2) The hysteresis loop of the ceramic sample was tested by ferroelectric analysis, and the remanent polarization intensity was determined by the hysteresis loop. The test results are shown in […]. Figure 3 The remanent polarization intensity P of the ceramic sample was obtained. r = 27 μC / cm 2 The ferroelectric properties of the ceramic sample were further enhanced.

[0099] (3) The dielectric behavior of the ceramic sample was measured using a high-temperature dielectric temperature spectrometer. The test results are shown in […]. Figure 4 It was found that by introducing 0.01 BAO, the Curie temperature of the ceramic material was further increased to 490 °C, which is beneficial for stabilizing and maintaining the piezoelectric properties at high temperatures.

[0100] (4) Quasi-static d 33 The measuring instrument was used to test the polarized ceramic sample at room temperature. The test results are shown below. Figure 5 The piezoelectric constant d of the 0.69BF-0.3BT-0.01BAO ceramic sample was obtained. 33 = 165 pC / N; k p = 0.326.

[0101] (5) The unipolar electrostriction curve of the ceramic sample was measured using a ferroelectric testing instrument under the conditions of room temperature, 50 kV / cm electric field, and 1 Hz test frequency. The test results are shown in […]. Figure 6 , Figure 7 The maximum electroinduced strain value S was obtained. max = 0.214% and inverse piezoelectric constant d 33 * = 530 pm / V, a further improvement compared to Comparative Example 1.

[0102] Table 1

[0103]

[0104] In Table 1, ac is the unit cell constant R. wp The GOF (God of Reasoning) values ​​reflect the reliability of the fit.

[0105] Example 3

[0106] (1) Prepare chemical reagents Bi2O3 (99.9%), Fe2O3 (99.9%), BaCO3 (99.9%), TiO2 (99.9%) and Al2O3 (99%).

[0107] (2) Weigh the chemical reagents in step 1 according to the chemical formula 0.685BF-0.3BT-0.015BAO on a high-precision analytical balance, and then place the powder mixture in a polytetrafluoroethylene ball mill jar, use anhydrous ethanol as the dispersion medium, and ball mill for 12 h at a speed of 290 r / min to ensure that the chemical reagents are fully mixed.

[0108] (3) The highly mixed slurry was dried in a high-temperature furnace. The dried powder was placed in an alumina crucible, covered with a crucible lid, and placed in a muffle furnace for pre-firing. The pre-firing temperature was set at 740 ℃ and held for 3 h. After pre-firing, the powder was placed in a ball mill jar and ball-milled in a planetary ball mill at a speed of 290 r / min for 12 h. The slurry was then removed and dried into powder.

[0109] (4) Add a polyvinyl alcohol aqueous solution binder with a mass fraction of 8 wt% to the obtained powder. The amount of polyvinyl alcohol aqueous solution added is 12% of the total powder mass. Stir and granulate, and then pass it through 80 mesh and 120 mesh sieves respectively before pressing into tablets. The molding pressure is set to 200 MPa. The powder is molded into round blanks with a diameter of 10 mm and a thickness of 1 mm.

[0110] (5) The wafer blanks are debinded in a muffle furnace. The debinding process involves slowly heating from room temperature to 570°C and holding at that temperature for 30 minutes, followed by natural cooling to room temperature. Then, the debinded wafer blanks are placed in a muffle furnace for sintering. Covering the wafer blanks with the corresponding powder using a buried firing method can effectively prevent element volatilization. The sintering temperature is set to 960°C, held for 4 hours, and then naturally cooled to room temperature.

[0111] (6) Polish the upper and lower surfaces of the ceramic material. Then, clean the polished ceramic in an ultrasonic cleaner for 10 min and dry it in a drying oven. After drying, coat the upper and lower surfaces of the ceramic sheet with a layer of silver paste. Finally, place the ceramic in a muffle furnace for silver firing. The temperature of the muffle furnace is set to 600 ℃ at a heating rate of 5 ℃ / min, hold for 30 min, and then cool naturally to obtain ceramic sample material that meets the requirements of electrical testing and engineering applications.

[0112] The performance of the 0.685BF-0.3BT-0.015BAO ceramic material prepared by the method of this embodiment was tested using the following methods.

[0113] (1) The 0.685BF-0.3BT-0.015BAO ceramic sample was tested using XRD and SEM. The test results are shown in the figure. Figure 1 Similar examples 1 and 2, Figure 1 It can be proven that BAO was successfully introduced into the BF-BT lattice. The ceramic exhibits a pure perovskite structure with both trigonal and tetragonal phases coexisting. The characteristic peak at (110) almost disappears, indicating that the ceramic sample is mainly tetragonal. The refined XRD data of Example 3 are shown in Table 1. It also matches the standard cards of trigonal phase of BF and tetragonal phase of BT, with a high degree of fitting confidence. Furthermore, the cell volume continues to decrease, indicating that more small-radius Al 3+ Successful integration. At this point, the tetragonal phase predominates in the sample (76%). Meanwhile, the SEM test results are shown below. Figure 2 It can be seen that after introducing 0.015 BAO into the matrix, the grain size of the ceramic sample is reduced, the sample surface is very dense, and there are no obvious visible pores and defects.

[0114] (2) The hysteresis loop of the ceramic sample was tested by ferroelectric analysis, and the remanent polarization intensity was determined by the hysteresis loop. The test results are shown in […]. Figure 3 The remanent polarization intensity P of the ceramic sample was obtained. r = 15.3 μC / cm 2 Excessive substitution also disrupts the local long-range ferroelectric order, causing the system to evolve towards a weak ferroelectric state, thereby leading to a decrease in macroscopic polarization capability.

[0115] (3) The dielectric behavior of the ceramic sample was measured using a high-temperature dielectric temperature spectrometer. The test results are shown in […]. Figure 4 It was found that by introducing 0.015 BAO, the Curie temperature of the ceramic material continued to increase to 498 °C.

[0116] (4) Quasi-static d 33 The measuring instrument was used to test the polarized ceramic sample at room temperature. The test results are shown below. Figure 5 The piezoelectric constant d of the ceramic sample was obtained. 33 = 160 pC / N; k p = 0.323. Al 3+ Excessive acceptor substitution leads to a strong "pinning effect" at grain boundaries and domain walls, severely limiting the reversible activity of electric domains during electromechanical coupling conversion, thus causing d 33 and k p It began to decline.

[0117] (5) The unipolar electrostriction curves of the ceramic samples were measured using a ferroelectric testing instrument under the conditions of room temperature, 50 kV / cm electric field, and 1 Hz test frequency. The test results are shown in […]. Figure 6 , Figure 7 The maximum electroinduced strain value S was obtained. max = 0.195% and inverse piezoelectric constant d 33 * = 501 pm / V.

[0118] Chinese invention patent application CN202510170887.7 discloses a piezoelectric ceramic material with high voltage performance and high temperature stability, in Pb[(Sb 1 / 2 Nb 1 / 2 ) x (Zr y Ti 0.98-y ) (1-x) Introducing an appropriate amount of BiAlO3 component into O3], through Bi 3+ Replacement radius close to Pb 2+ This causes local lattice distortion, although the measured piezoelectric coefficient d 33 Due to the presence of a lead matrix, the initial piezoelectric coefficient d was relatively high. After introducing BiAlO3 in Examples 1, 2, and 3 (1%, 2%, and 3% respectively), the piezoelectric coefficient d... 33 The values ​​are 340, 337, and 336 pC / N, respectively; the piezoelectric coefficients all remain within a certain range without significant increase. Curie temperature T c In Examples 1, 2, and 3, the temperatures were 347, 340, and 337 °C, respectively, and there was no increase in temperature with increasing BiAlO3 doping concentration. Although this technique introduces BiAlO3, it does not regulate the phase structure of the ceramic material; all ceramic samples showed no significant changes in XRD patterns or phase structure. In this technique, the BiAlO3 component mainly functions as an ion substitution dopant. In contrast, the BiAlO3 in this invention improves piezoelectric properties by adjusting the ratio of trigonal and tetragonal phases in the 0.7BF-0.3BT ceramic to form quasi-isomorphic phase boundaries, as shown in Table 1. Figure 5 The piezoelectric coefficient d is shown compared to the comparative example. 33 The value is 118 pC / N. In Example 2, after constructing MPB, d 33 The Curie temperature was increased to 165 pC / N, showing a significant improvement over the comparative example in Example 2. c Because of the low tolerance factor of BiAlO3, this invention also significantly improves upon it. Figure 4 Curie temperature T cThe temperature gradually increased from 478℃ in the comparative example to 498℃ with increasing BiAlO3 content. It is evident that although both this invention and Chinese invention patent application CN202510170887.7 introduce BiAlO3, the roles and mechanisms of the BiAlO3 component are different. In particular, Chinese invention patent application CN202510170887.7 uses lead-containing piezoelectric ceramic materials, which presents significant environmental problems. In contrast, this invention uses lead-free piezoelectric ceramic materials, offering clear environmental advantages.

[0119] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material, characterized in that, The chemical formula is (0.7-x)BiFeO3-0.3BaTiO3-xBiAlO 3， Where x = 0.005~0.015, x represents the mole fraction.

2. A method for preparing the bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 1, characterized in that, Includes the following steps: (1) Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2 and Al2O3 according to their chemical formulas and prepare them into powder; (2) The powder is granulated and formed into an embryo; (3) Perform degumming treatment on the embryo; (4) The preform after debinding treatment is sintered to obtain ceramic material; (5) The ceramic material is subjected to silver plating polarization treatment to obtain bismuth ferrite-barium titanate based high temperature lead-free piezoelectric ceramic material.

3. The preparation method of a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 2, characterized in that, In step (1), when preparing the powder, the weighed raw materials are subjected to ball milling, drying, pre-calcination and ball milling in sequence, and the resulting slurry is taken out and dried into powder.

4. The preparation method of a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 3, characterized in that, In both ball milling processes, the ball mill speed was 280-320 r / min, and the ball milling time was 10-12 h. During the pre-firing process, the temperature is controlled at 730-750 ℃, and the holding time is 3-4 h.

5. The preparation method of a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 2, characterized in that, In step (2), the preparation of the preform involves adding a binder to the obtained powder, stirring and granulating it, sieving it after granulation, and then pressing it into a sheet on a hydraulic press; the preform is in the shape of a disc.

6. The method for preparing a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 5, characterized in that, The adhesive is a polyvinyl alcohol aqueous solution with a mass concentration of 5%-10% and an addition amount of 10-12% of the total mass of the powder; the sieve size for the sieving process is 80-100 mesh; the diameter of the disc-shaped preform is 10-11 mm and the thickness is 0.9 mm to 1.1 mm.

7. The preparation method of a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 2, characterized in that, In step (3), the glue removal process involves slowly heating the room temperature to 550-600 ℃ and holding it at that temperature for 20-30 minutes, followed by natural cooling to room temperature.

8. The method for preparing a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 2, characterized in that, In step (4), the sintering method is buried firing; In step (5), the process of silvering the ceramic material involves polishing the upper and lower surfaces of the ceramic material, ultrasonically cleaning and drying it, coating the upper and lower surfaces of the dried ceramic sheet with a layer of silver paste with a diameter of 6-8 mm, drying it, and then performing a silver firing process to obtain a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material.

9. The preparation method of a bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 8, characterized in that, The sintering process involves burying the disc blank with pre-fired powder in the same proportion as the blank, followed by sintering. The sintering temperature is controlled at 960 ℃~980 ℃, and the holding time is 3-4 h. The drying is carried out in an oven; the silver burning process is carried out in a muffle furnace.

10. The application of the bismuth ferrite-barium titanate-based high-temperature lead-free piezoelectric ceramic material according to claim 1 in the preparation of piezoelectric ceramic components.

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