A method for preparing piezoelectric ceramics that directly obtains piezoelectric properties

Abstract

This invention belongs to the field of lead-free piezoelectric ceramics, and particularly relates to a method for preparing piezoelectric ceramics that directly obtains piezoelectric properties. The method includes the following steps: (1) preparing BDTbT-CCdW via a solid-state reaction method, and grinding the synthesized BDTbT-CCdW into submicron powder using a colloid mill; (2) preparing BaASTB glass powder via a containerless air suspension process; (3) uniformly mixing the BDTbT-CCdW powder and BaASTB glass powder using a high-energy ball mill; (4) preparing BT-based piezoelectric ceramics via rapid calcination and cooling. During the rapid cooling process, the glassy phase BaASTB pins to the grain boundaries, shrinks to generate compressive stress, and induces piezoelectric properties, allowing BT-based ceramics to directly obtain piezoelectric properties without polarization and without depolarization.

Description

Technical Field

[0001] This invention relates to the field of lead-free piezoelectric ceramics, and more particularly to a method for preparing piezoelectric ceramics that directly obtains piezoelectric properties. Background Art

[0002] Lead zirconate titanate-based piezoelectric ceramics almost monopolize the field of piezoelectric applications, finding widespread use in piezoelectric actuators and transducers. However, the high toxicity of lead makes the development of lead-free piezoelectric materials an urgent priority.

[0003] Barium titanate (BaTiO3, BT) is the earliest discovered piezoelectric ceramic. Its piezoelectric properties can be significantly improved through A-site and B-site solid solution and the introduction of defects, making it a promising candidate material to replace lead-based piezoelectric materials. This invention, combining defect engineering and the addition of a Bi-based second component, can appropriately lower the sintering temperature, reduce shrinkage stress during rapid cooling, increase the sintering yield, and improve the piezoelectric properties of BT-based ceramics.

[0004] Piezoelectric ceramics are all polycrystalline materials, requiring DC polarization, AC polarization, or pulsed polarization to achieve piezoelectric properties. This necessitates expensive high-voltage polarization equipment and increases the number of steps in the piezoelectric material preparation process. Piezoelectric materials have a Curie temperature; the piezoelectric properties obtained through polarization can be lost due to depolarization caused by external forces or temperature fields. Therefore, it is necessary to develop a method for preparing piezoelectric ceramics that directly achieves piezoelectric properties without depolarization.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing piezoelectric ceramics that directly obtains piezoelectric properties, thereby solving the technical problem that piezoelectric ceramics need to be polarized to obtain piezoelectric properties and that there is a possibility of depolarization.

[0007] The microstructure of polycrystalline piezoelectric ceramics consists of grains and grain boundaries. A method for directly obtaining piezoelectric properties by inducing ferroelectric domain orientation is provided by utilizing a low-melting-point glassy phase pinned to the grain boundaries and generating compressive stress through the difference in thermal expansion coefficients between the grain boundary phase and the grain phase. This invention prepares a low-temperature glassy phase via melt quenching, then uniformly mixes the glassy phase with BT-based powder through liquid-phase dispersion and high-energy ball milling. The ceramic is then sintered by rapid firing and quenching. The grain boundary glassy phase contracts due to the difference in thermal expansion coefficients, generating uniform compressive stress, providing a new approach to preparing piezoelectric ceramics that directly obtain piezoelectric properties without depolarization.

[0008] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0009] A method for preparing piezoelectric ceramics that directly achieve piezoelectric properties includes the following steps:

[0010] (1) BDTbT-CCdW was prepared by solid-state reaction method, and the synthesized BDTbT-CCdW was ground into submicron powder by colloid mill;

[0011] (2) Preparation of BaASTB glass powder by containerless air suspension process;

[0012] (3) Use a high-energy ball mill to mix BDTbT-CCdW powder and BaASTB glass powder evenly;

[0013] (4) BT-based piezoelectric ceramics were prepared by rapid calcination and quenching.

[0014] This invention prepares BDTbT-CCdW ceramics by rapid sintering. Through rapid sintering and quenching, the glassy phase BaASTB is pinned to the grain boundaries. By utilizing the difference in thermal expansion coefficients, the glassy phase pinned to the grain boundaries generates permanent compressive stress, which induces piezoelectric properties. This allows BT-based ceramics to directly obtain piezoelectric properties without polarization and without depolarization.

[0015] Specifically, during the sintering process of BDTbT-CCdW ceramic materials, the glassy phase BaASTB is distributed on the grain boundaries, forming a "nail"-like effect that tightly binds the ceramic grains together. The presence of this glassy phase restricts movement between grain boundaries, hence the term "pinning effect." Grain boundary movement, to a certain extent, determines the mechanical and electrical properties of the ceramic; pinning grain boundaries can improve the structural stability of the ceramic. The glassy phase BaASTB typically has a different coefficient of thermal expansion than the matrix ceramic. During rapid firing and quenching, due to this difference in thermal expansion, the volume change of the glassy phase during cooling is inconsistent with that of the matrix ceramic, resulting in a "contraction mismatch" at the grain boundaries. Because the expansion of the glassy phase is relatively small or its contraction is relatively large, the matrix ceramic experiences an inward contraction stress at the grain boundaries; this stress is called "permanent compressive stress." This permanent compressive stress caused by the pinning effect can suppress the movement of domain walls within the grains. The movement of domain walls is crucial for the polarization or depolarization of piezoelectric ceramics. When domain walls are fixed by permanent compressive stress, the spontaneous polarization direction inside the ceramic is "frozen," allowing the material to exhibit piezoelectric properties even without polarization treatment. This "frozen" polarization direction endows the material with permanent piezoelectric properties.

[0016] Preferably, in step (1), the chemical formula of BDTbT-CCdW is (1-z)(Ba 1-x Dy x (Tb) y Ti 1-y )O3-zCa(Cd0.5 W 0.5 )O3, where x=0.025-0.075, y=0.025-0.1, z=0.025-0.125.

[0017] In this invention, the doping amounts of yttrium (Dy) and terbium (Tb) are in the ranges of 0.025-0.075 and 0.025-0.1%, respectively, which allows for fine-tuning of the lattice structure of the material to achieve optimal piezoelectric properties. These concentrations of yttrium and terbium ions can introduce appropriate lattice distortion, thereby improving the piezoelectric constant and dielectric properties. Controlling the doping concentration range within a low doping range (2.5%-10%) helps optimize the piezoelectric and dielectric properties of the material without destroying the original perovskite structure, while maintaining good stability at high temperatures. The doping ranges of x and y stabilize the perovskite lattice structure, improving not only piezoelectric properties but also the structural stability of the material in thermal environments. Ca(Cd) 0.5 W 0.5 The addition of O3, controlled at 0.025-0.125%, enhances the grain boundary pinning effect and helps lower the sintering temperature of the material, enabling the formation of dense ceramics at lower temperatures. This component helps promote the liquid phase sintering process, thereby reducing sintering time and energy consumption, and saving production costs.

[0018] As a preferred embodiment, in step (1), the fully dried analytical grade raw material is accurately weighed according to the stoichiometric ratio, ground and mixed evenly, and then calcined at 1300-1350℃ for 2 hours; the calcined BDTbT-CCdW is pulverized and ground with a colloid mill at a speed of 4500 rpm, a water cooling pressure of 0.3 MPa, a wet three-stage grinding process, and a flow rate of 0.5 L / h. After drying, submicron BDTbT-CCdW powder is obtained.

[0019] As a preferred option, the analytically pure raw materials include BaCO3, Dy2O3, Tb4O7, TiO2, CaCO3, CdO and WO3 in a molar ratio of 2.5:5:24.5:3:0.5.

[0020] Preferably, in step (2), containerless gas levitation is a unique method for synthesizing materials. Its core purpose is to improve the purity and performance of the material by avoiding contact between the material and the container and reducing impurity contamination. Specifically, this process involves the following steps in the synthesis of BaASTB glass powder:

[0021] Raw material preparation and pressing into tablets: Accurately weigh the analytically pure raw materials according to the stoichiometric ratio, grind and mix them evenly, and then press the raw materials into small round tablets (e.g., 5mm in diameter and 3mm in thickness).

[0022] Preliminary calcination: The discs are calcined at 1050℃ for 4 hours to ensure that the material reacts fully and forms a certain crystal phase structure.

[0023] Containerless gas suspension melting: In a melting furnace, a disc is suspended by an airflow. Oxygen is usually used to suspend the sample, which avoids contact between the sample and the container wall and effectively reduces defects caused by contamination. The disc in the suspended state is heated to 1500°C and held for 5 minutes to completely melt it. After melting, the sample is quickly placed in an ice-water mixture for quenching, which can form BaASTB glass powder with a glass structure.

[0024] Drying: Finally, the quenched glass powder is dried to obtain the final BaASTB glass powder.

[0025] Preferably, in step (3), the mass ratio of BDTbT-CCdW powder to BaASTB glass powder is BaASTB:BDTbT-CCdW = 1.5-3.5 wt%. That is, the glass powder accounts for 1.5-3.5% of the ceramic powder by mass. If the BaASTB content is too high, the amount of glass phase in the ceramic matrix may be excessive, causing the original perovskite structure to be covered by too much glass phase, thereby changing the lattice structure of the ceramic matrix and affecting the overall performance of the ceramic material. The present invention selects a ratio range of 1.5-3.5 wt%, which can obtain an effective pinning effect without introducing too much glass phase, ensuring the tight bonding between grains.

[0026] Preferably, in step (3), zirconia balls are used as the grinding medium, wet ball milling is performed, the high-energy ball mill speed is 800 rpm, and the ball milling time is 4 hours.

[0027] Preferably, in step (4), polyvinyl alcohol is added to the BDTbT-CCdW and BaASTB mixture obtained in step (3) for granulation and pressing. The binder is removed at 600°C, and the blank after binder removal is rapidly sintered and quenched in air to prepare BT-based ceramics. The sintering temperature is 1475-1525°C and the sintering time is 60-90 min. After sintering, the blank is rapidly cooled to room temperature. Permanent compressive stress is generated during the cooling process. This stress fixes the polarization direction of the crystal, allowing the piezoelectric properties to be generated spontaneously without external polarization treatment.

[0028] Polyvinyl alcohol (PVA) acts as a binder during granulation and tableting, enabling the mixture to be formed into uniform and dense granules, improving the compressibility of the mixture and the final molding effect. After debinding at 600℃, the PVA is fully removed, making the ceramic blank denser and reducing the porosity that may exist inside the material during sintering, thereby improving the overall density of the ceramic and contributing to its mechanical strength and electrical properties.

[0029] The rapid firing and quenching process generates permanent compressive stress through differences in thermal expansion. This compressive stress is applied to the grain boundaries of the ceramic during cooling, helping to pin the grain boundaries, fix the polarization direction within the crystal, and suppress domain wall movement. This fixed polarization direction is the spontaneous polarization direction, which enables the ceramic to possess piezoelectric properties without external polarization treatment, simplifying subsequent processing steps.

[0030] By employing the above technical solution, the present invention has at least the following beneficial effects:

[0031] Traditional piezoelectric ceramics typically require polarization (through an external strong electric field) to orient the polarization domains within the material, thereby achieving piezoelectric properties. However, these domains may reorient randomly when exposed to high temperatures or mechanical shocks, leading to a degradation of piezoelectric properties, a phenomenon known as "depolarization." In this invention, the permanent compressive stress formed by the grain boundary pinning effect prevents the domains from easily moving. This ensures that even when exposed to high temperatures or other external disturbances during use, the polarization direction remains unchanged, effectively preventing depolarization.

[0032] This invention employs a containerless air suspension process. Since there is no container restriction, the molten material can completely avoid the introduction of impurities, resulting in high purity of the glass powder, while also achieving good uniformity and controllable structural characteristics. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is the impedance resonance diagram characterizing the electromechanical coupling coefficient in Embodiment 1 of the present invention. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0036] This invention involves uniformly mixing BDTbT-CCdW powder prepared by a solid-state reaction method and BaASTB glass powder prepared by a containerless air suspension process using a high-energy ball mill. The mixture is then rapidly sintered and quenched to prepare BT-based piezoelectric ceramics. During the quenching process, the glassy BaASTB phase pins to the grain boundaries of the BT-based ceramic, shrinking to generate sustained and uniform compressive stress, inducing piezoelectric properties. This allows the BT-based ceramics to directly acquire piezoelectric properties without polarization and without depolarization. The piezoelectric constant d of the piezoelectric ceramics prepared by this invention is... 33 =238-252pC / N, electromechanical coupling coefficient K p =0.390-0.398.

[0037] Example 1

[0038] (1) 0.95 (Ba) was prepared by the traditional solid-state reaction method. 0.975 Dy 0.025 (Tb) 0.05 Ti 0.95 O3-0.05Ca(Cd) 0.5 W 0.5 The specific steps for preparing BDTbT-0.05CCdW (BDTbT-0.05CCdW) are as follows: Accurately weigh fully dried analytical grade BaCO3, Dy2O3, Tb4O7, TiO2, CaCO3, CdO, and WO3 according to the stoichiometric ratio, mix them evenly, and calcine at 1315℃ for 2 hours. The calcined BDTbT-0.05CCdW is then pulverized and ground using a colloid mill at 4500 rpm, with water cooling at a pressure of 0.3 MPa, using a three-stage wet grinding process at a flow rate of 0.5 L / h. After drying, submicron BDTbT-0.05CCdW powder is obtained.

[0039] (2) BaASTB glass powder was prepared by containerless air suspension process. The specific steps were as follows: the fully dried analytical grade raw materials were accurately weighed according to the stoichiometric ratio of 2.5BaSO4-5Al2O3-24.5SiO2-3TiO2-0.5B2O3, ground and mixed evenly, and then pressed into discs with a diameter of 5 mm and a thickness of 3 mm. The discs were calcined at 1050℃ for 4 h. The calcined discs were melted by containerless air suspension process at a melting temperature of 1500℃ for 5 min. After melting, the discs were quenched in an ice-water mixture and dried to obtain BaASTB glass powder.

[0040] (3) BT-based piezoelectric ceramics were prepared by rapid sintering and quenching. The specific steps were as follows: BDTbT-0.05CCdW powder and BaASTB glass powder were mixed evenly using a high-energy ball mill. The mass ratio of BDTbT-0.05CCdW powder to BaASTB glass powder was BaASTB:BDTbT-0.05CCdW = 2.5wt%. Zirconia balls were used as the grinding medium for wet ball milling at 800 rpm for 4 hours. The evenly mixed BDTbT-0.05CCdW and BaASTB were granulated and pressed into tablets with an appropriate amount of polyvinyl alcohol. The binder was removed at 600℃. The blank after binder removal was rapidly sintered and quenched in air at 1500℃ for 60 minutes to prepare BT-based ceramics. After rapid sintering, the ceramics were quenched to room temperature to obtain BT-based ceramics. The piezoelectric constant d was measured. 33 =245pC / N, electromechanical coupling coefficient K p =0.394.

[0041] Example 2

[0042] (1) Preparation of 0.975 (Ba) by solid-state reaction method 0.925 Dy 0.075 (Tb) 0.025 Ti 0.975 O3-0.025Ca(Cd) 0.5 W 0.5 The specific steps for preparing BDTbT-0.025CCdW (BDTbT-0.025CCdW) are as follows: Accurately weigh fully dried analytical grade BaCO3, Dy2O3, Tb4O7, TiO2, CaCO3, CdO, and WO3 according to the stoichiometric ratio. Mix them evenly and calcine at 1350℃ for 2 hours. The calcined BDTbT-0.025CCdW is then pulverized and ground using a colloid mill at 4500 rpm, with water cooling at a pressure of 0.3 MPa, using a three-stage wet grinding process at a flow rate of 0.5 L / h. After drying, submicron BDTbT-0.025CCdW powder is obtained.

[0043] (2) BaASTB glass powder was prepared by containerless air suspension process. The specific steps were as follows: the fully dried analytical grade raw materials were accurately weighed according to the stoichiometric ratio of 2.5BaSO4-5Al2O3-24.5SiO2-3TiO2-0.5B2O3, ground and mixed evenly, and then pressed into discs with a diameter of 5 mm and a thickness of 3 mm. The discs were calcined at 1050℃ for 4 h. The calcined discs were melted by containerless air suspension process at a melting temperature of 1500℃ for 5 min. After melting, the discs were quenched in an ice-water mixture and dried to obtain BaASTB glass powder.

[0044] (3) BT-based piezoelectric ceramics were prepared by rapid sintering and quenching. The specific steps were as follows: BDTbT-0.025CCdW powder and BaASTB glass powder were mixed evenly using a high-energy ball mill. The mass ratio of BDTbT-0.025CCdW powder to BaASTB glass powder was BaASTB:BDTbT-0.025CCdW = 1.5wt%. Zirconia balls were used as the grinding medium for wet ball milling at 800 rpm for 4 hours. The evenly mixed BDTbT-0.025CCdW and BaASTB were granulated and pressed into tablets with an appropriate amount of polyvinyl alcohol. The binder was removed at 600℃. The blank after binder removal was rapidly sintered and quenched in air at 1525℃ for 30 minutes. After rapid sintering, the blank was quenched to room temperature to obtain BT-based ceramics. The piezoelectric constant d was measured. 33 =238pC / N, electromechanical coupling coefficient K p =0.390.

[0045] Example 3

[0046] (1) 0.875 (Ba) was prepared by the traditional solid-state reaction method. 0.95 Dy 0.05 (Tb) 0.1 Ti 0.9 O3-0.125Ca(Cd) 0.5 W 0.5 The specific steps for preparing BDTbT-0.125CCdW (BDTbT-0.125CCdW) are as follows: Accurately weigh fully dried analytical grade BaCO3, Dy2O3, Tb4O7, TiO2, CaCO3, CdO, and WO3 according to the stoichiometric ratio, mix them evenly, and calcine at 1300℃ for 2 hours. The calcined BDTbT-0.125CCdW is then pulverized and ground using a colloid mill at 4500 rpm, water cooling pressure of 0.3 MPa, and a three-stage wet grinding process with a flow rate of 0.5 L / h. After drying, submicron BDTbT-0.125CCdW powder is obtained.

[0047] (2) BaASTB glass powder was prepared by containerless air suspension process. The specific steps were as follows: the fully dried analytical grade raw materials were accurately weighed according to the stoichiometric ratio of 2.5BaSO4-5Al2O3-24.5SiO2-3TiO2-0.5B2O3, ground and mixed evenly, and then pressed into discs with a diameter of 5 mm and a thickness of 3 mm. The discs were calcined at 1050℃ for 4 h. The calcined discs were melted by containerless air suspension process at a melting temperature of 1500℃ for 5 min. After melting, the discs were quenched in an ice-water mixture and dried to obtain BaASTB glass powder.

[0048] (3) BT-based piezoelectric ceramics were prepared by rapid sintering and quenching. The specific steps were as follows: BDTbT-0.125CCdW powder and BaASTB glass powder were mixed evenly using a high-energy ball mill. The mass ratio of BDTbT-0.125CCdW powder to BaASTB glass powder was 3.5wt% (BaASTB:BDTbT-0.125CCdW). Zirconia balls were used as the grinding medium for wet ball milling at 800 rpm for 4 hours. The evenly mixed BDTbT-0.125CCdW and BaASTB were granulated and pressed into tablets with an appropriate amount of polyvinyl alcohol. The binder was removed at 600℃. The blank after binder removal was rapidly sintered and quenched in air at 1475℃ for 90 minutes. After rapid sintering, the blank was quenched to room temperature to obtain BT-based ceramics. The piezoelectric constant d was measured. 33 =252pC / N, electromechanical coupling coefficient K p =0.398.

[0049] The scope of this invention is not limited to Dy and Tb-doped barium titanate (Ba 1-x Dy x (Tb) y Ti 1-y The preparation of O3-based ceramics is also applicable to the doping of other rare earth elements with barium titanate (Ba3). 1-x Re x (Tb) y Re¢ 1-y Preparation of O3-based ceramics. Rare earth elements generally have similar electronic shell structures, especially the lanthanide rare earth elements, which have similar 4f electron configurations, resulting in similar chemical properties and lattice coordination effects in material doping. Therefore, this invention can be applied to other rare earth-doped systems to obtain piezoelectric ceramics that directly achieve piezoelectric properties without polarization and do not depolarize.

[0050] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing piezoelectric ceramics that directly obtain piezoelectric properties, characterized in that: The following steps are included: (1) BDTbT-CCdW was prepared by solid-state reaction method. The synthesized BDTbT-CCdW was ground into submicron powder by colloid mill. The chemical formula of BDTbT-CCdW is (1-z)(Ba 1-x Dy x (Tb) y Ti 1-y )O3-zCa(Cd 0.5 W 0.5 O3, where x = 0.025 - 0.075, y = 0.025 - 0.1, z = 0.025 - 0.125; (2) Glass powder BaASTB was prepared by containerless air suspension process. BaASTB was prepared by BaSO4, Al2O3, SiO2, TiO2 and B2O3 in a molar ratio of 2.5:5:24.5:3:0.

5. (3) Use a high-energy ball mill to mix BDTbT-CCdW powder and BaASTB glass powder evenly. The mass ratio of BDTbT-CCdW powder to BaASTB glass powder is: BaASTB:BDTbT-CCdW = 1.5-3.5 wt%. (4) Polyvinyl alcohol is added to the mixture of BDTbT-CCdW and BaASTB obtained in step (3) for granulation and pressing. The glue is removed at 600℃. The blank after glue removal is prepared by rapid firing and quenching in air atmosphere to prepare BT-based piezoelectric ceramics. The rapid firing temperature is 1475-1525℃ and the rapid firing time is 60-90min. After the rapid firing is completed, it is quenched to room temperature.

2. The method for preparing piezoelectric ceramics with directly obtained piezoelectric properties according to claim 1, characterized in that: In step (1), the fully dried analytical grade raw material is accurately weighed according to the stoichiometric ratio, ground and mixed evenly, and then calcined at 1300-1350℃ for 2 hours. After calcination, the BDTbT-CCdW is pulverized and ground with a colloid mill at a speed of 4500 rpm, a water cooling pressure of 0.3 MPa, a wet three-stage grinding process, and a flow rate of 0.5 L / h. After drying, submicron BDTbT-CCdW powder is obtained.

3. The method for preparing piezoelectric ceramics with directly obtained piezoelectric properties according to claim 2, characterized in that: The analytical grade raw materials include BaCO3, Dy2O3, Tb4O7, TiO2, CaCO3, CdO, and WO3.

4. The method for preparing piezoelectric ceramics with directly obtained piezoelectric properties according to claim 1, characterized in that: In step (2), the preparation method of the glass powder BaASTB is as follows: The fully dried analytical grade raw material was accurately weighed according to the stoichiometric ratio, ground and mixed evenly, and then pressed into discs with a diameter of 5 mm and a thickness of 3 mm. The discs were calcined at 1050℃ for 4 hours. The calcined discs were melted using a containerless air suspension process at a melting temperature of 1500℃ for 5 minutes. After melting, the discs were quenched in an ice-water mixture and dried to obtain BaASTB glass powder.

5. The method for preparing piezoelectric ceramics with directly obtained piezoelectric properties according to claim 1, characterized in that: In step (3), zirconia balls are used as the grinding medium and wet ball milling is performed. The high-energy ball mill rotates at 800 rpm and the ball milling time is 4 hours.

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