A sodium bismuth titanate-based lead-free piezoelectric texture ceramic and a preparation method thereof

Abstract

The application provides a sodium bismuth titanate-based lead-free piezoelectric texture ceramic and a preparation method thereof. 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 1‑x Ta x O3, 0 < x < 0.01, and the texture degree of the sodium bismuth titanate-based lead-free piezoelectric texture ceramic is greater than 90%. The lead-free piezoelectric texture ceramic is highly oriented, the high orientation of the grain is beneficial to greatly improving the residual polarization intensity, thereby improving the piezoelectric performance, and is an anisotropic piezoelectric ceramic with excellent piezoelectric performance. The application further provides the preparation method of the sodium bismuth titanate-based lead-free piezoelectric texture ceramic.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric ceramics technology, specifically relating to a sodium bismuth titanate-based lead-free piezoelectric textured ceramic and its preparation method. Background Technology

[0002] Piezoelectric ceramics, as materials capable of converting electrical energy into mechanical energy, are widely used in various fields such as actuators and micro-displacement devices due to their large electric field-induced strain. Although lead-based piezoelectric ceramics have advantages in electrical properties and stability, the toxicity and environmental hazards of their main raw material, lead oxide, have prompted researchers to seek lead-free alternatives.

[0003] Sodium bismuth titanate-based lead-free piezoelectric ceramics have attracted attention due to their superior electrostrain and high Curie temperature; however, their performance has not yet matched that of lead-based materials, thus requiring modification and optimization to enhance their application potential. Common modification methods include multi-component solid solution, ion doping, and improvements in the preparation process. Multi-component solid solution involves introducing components with different perovskite structures to form a solid solution with sodium bismuth titanate-based lead-free piezoelectric ceramics, creating quasi-isomorphic phase boundaries and significantly improving their electrical properties, thereby enhancing piezoelectric performance. Ion doping, on the other hand, introduces rare earth elements or low-melting-point elements to alter the crystal structure and improve electrical properties. Grain orientation is closely related to the piezoelectric properties of the material. Randomly oriented polycrystalline ceramics can have their grains oriented during preparation using texturing techniques, exhibiting superior performance in a specific direction. Currently, grain orientation technology is the most commonly used method for preparing textured ceramics, which can be achieved by adding template grains and using tape casting.

[0004] However, existing lead-free piezoelectric ceramics cannot simultaneously achieve ideal electrical properties while maintaining high texture, density, and purity. Therefore, there is still a need to develop a new type of lead-free piezoelectric ceramic. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a sodium bismuth titanate-based lead-free piezoelectric textured ceramic that, while possessing ideal electrical properties, also maintains high texture, density, and high purity.

[0006] The present invention also provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric textured ceramics.

[0007] The first aspect of the present invention provides a sodium bismuth titanate-based lead-free piezoelectric textured ceramic with the chemical composition [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr0.04 Ti 1-x Ta x O3, 0< x <0.01, the texture of the sodium bismuth titanate-based lead-free piezoelectric textured ceramic is >90%.

[0008] One technical solution of the present invention concerning sodium bismuth titanate-based lead-free piezoelectric textured ceramics has at least the following beneficial effects:

[0009] The sodium bismuth titanate-based lead-free piezoelectric textured ceramic of this invention has highly oriented grains. This high grain orientation significantly enhances its remanent polarization, thereby improving its piezoelectric properties. It is an anisotropic piezoelectric ceramic with excellent piezoelectric performance. It maintains high texture, density, and high purity while possessing ideal electrical properties.

[0010] According to some embodiments of the present invention, x The preferred range is 0.003 < x <0.009.

[0011] According to some embodiments of the present invention, the textured ceramic grains of the sodium bismuth titanate-based lead-free piezoelectric textured ceramic are along... <001> orientation.

[0012] According to some embodiments of the present invention, x is 0.006, and the chemical composition of the sodium bismuth titanate-based lead-free piezoelectric textured ceramic is [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 O3.

[0013] [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 O3 lead-free piezoelectric textured ceramics exhibit high electrostrain performance among randomly oriented ceramics, thus textured ceramics can be used to further improve their properties.

[0014] A second aspect of the present invention provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric textured ceramics according to the first aspect of the present invention, comprising the following steps:

[0015] Bismuth titanate template crystals were prepared using a single molten salt system. Based on the chemical composition, the bismuth titanate template crystals, titanium dioxide, sodium carbonate, potassium carbonate, strontium carbonate, and tantalum pentoxide were weighed and mixed with bismuth oxide, additives, and solvents to obtain a ceramic slurry. The ceramic slurry was then cast using a reactive template grain growth method and a casting process to obtain a single-layer cast film. The single-layer cast films were stacked to obtain a cast film sheet. The cast film sheet was then subjected to hot pressing, a first cold isostatic pressing, debinding, a second cold isostatic pressing, and sintering to obtain the sodium bismuth titanate-based lead-free piezoelectric textured ceramic.

[0016] One technical solution of the present invention relating to the preparation method of sodium bismuth titanate-based lead-free piezoelectric textured ceramics has at least the following beneficial effects:

[0017] When preparing piezoelectric textured ceramics with high electrostriction, researchers often use a sodium chloride-potassium chloride (NaCl-KCl) composite molten salt system to prepare bismuth titanate template grains via the molten salt method. This results in grains of varying sizes, and the high preparation temperature leads to the presence of impurity phases within the template grains, affecting the stoichiometry of the textured ceramic. Consequently, the final bismuth titanate template grains are relatively small in orientation, contain impurity phases, and have a large size range, making it impossible to prepare high-purity, large-size sheet-like bismuth titanate template grains. To obtain high-purity lead-free piezoelectric ceramics that can improve electrical properties through doping modification while maintaining high texture and density, further optimization of the preparation process is urgently needed. This invention is based on further improving BNKT (Bi 0.5 Na 0.84 K 0.16 ) 0.5 TiO3-0.45(Bi 0.1 Sr 0.85 The piezoelectric properties of TiO3-based ceramics were improved by co-doping of A-site and B-site ions in a binary solid solution of sodium bismuth titanate-potassium bismuth titanate (BNT-BKT). Using a single molten salt system combined with texturing technology (reactive template grain growth method), the ceramic crystal structure was altered using suitable templates and tape casting processes, resulting in an ordered arrangement of ceramic grains and thus obtaining anisotropic piezoelectric ceramics with excellent piezoelectric properties. This can provide a reference for the industry in preparing templated and textured ceramics, further promoting the practical application of lead-free piezoelectric ceramics.

[0018] The preparation method of this invention uses sheet-like doped bismuth titanate with the same composition as the doped sodium bismuth titanate ceramic powder as a template. Since the reaction template grain growth method involves mixing the template and the drug powder together, stacking them, and then sintering, during the sintering process, the template grains engulf the surrounding drug powder and participate in the reaction. Therefore, the identical composition avoids the internal stress caused by different lattice constants that would result after the template grains engulf the surrounding drug powder particles and participate in the reaction, thus preventing the internal stress from affecting the piezoelectric properties.

[0019] The preparation method of the present invention is simple, easy to operate, and low in cost, which can save experimental costs and equipment investment.

[0020] According to some embodiments of the present invention, the bismuth titanate template crystal is plate-shaped and has the chemical formula Bi₄Ti₃O₃. 12 .

[0021] Bismuth titanate template crystals, due to their lamellar structure, good thermal stability, and presence of BNT-related elements, are the most commonly used template grains in the RTGG method for preparing BNT-based textured ceramics. The bismuth titanate template grains are pre-arranged or distributed in a specific orientation. When other reactants (such as precursor powders) are introduced and a chemical reaction occurs, the newly formed BNT matrix phase grows along the orientation of the bismuth titanate template grains, thereby improving the overall texture of the ceramic material. Bismuth titanate itself may participate in the chemical reaction, transforming into part of the BNT matrix phase through solid-state reactions, liquid-state sintering, etc., while retaining its original texture. Because textured ceramics have a more consistent crystal orientation, they often exhibit better electrical, mechanical, and other physical properties.

[0022] According to some embodiments of the present invention, the preparation method of the bismuth titanate template crystal includes the following steps: mixing Bi2O3 and TiO2, adding a single molten salt, and then ball milling, drying and calcining to obtain the bismuth titanate template crystal.

[0023] According to some embodiments of the present invention, the single molten salt is a KCl molten salt system.

[0024] According to some embodiments of the present invention, the method for preparing the bismuth titanate template crystal may be:

[0025] First, react Bi₂O₃ and TiO₂ according to the chemical reaction equation: 2Bi₂O₃ + 3TiO₂ → Bi₄Ti₃O 12 Formula calculations were performed, and bismuth oxide and titanium dioxide were weighed and mixed according to the molar ratio. A single potassium chloride (KCl) molten salt was selected as the molten salt system. The mass ratio of molten salt (KCl) to the reaction raw materials (Bi2O3 and TiO2) can be 1.5:1.

[0026] After weighing, the sample was placed in a ball mill jar and mixed for 4 hours at 300 rpm using zirconia balls and anhydrous ethanol as solvent in a planetary ball mill. The resulting slurry was dried at 80°C. The dried powder was then placed in a corundum crucible, sealed with the crucible lid, and placed in a muffle furnace for synthesis to prevent the large-scale volatilization of molten salt and Bi at high temperatures. The synthesis process involved heating to 1140°C at room temperature at a heating rate of 5°C / min and holding for 8 hours, followed by cooling to 300°C at a rate of 3°C / min and then cooling with the furnace. The synthesized powder was then added to deionized water at 80-100°C and stirred, dispersed, and washed multiple times. After discarding the supernatant, the powder in the beaker was finally dried to obtain flake-like Bi₄Ti₃O₃ prepared in a pure KCl system. 12 Template grains.

[0027] According to some embodiments of the present invention, the additives include polyvinyl butyral, dibutyl phthalate, polyethylene glycol, and castor oil.

[0028] According to some embodiments of the present invention, the castor oil accounts for 1 to 3% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide, and bismuth oxide.

[0029] According to some embodiments of the present invention, the castor oil mass accounts for any one of the following values ​​or a range formed by any two of the total mass of bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide: 1%, 1.5%, 2%, 2.5% and 3%, such as 1.5 to 2.5%.

[0030] According to some embodiments of the present invention, the castor oil accounts for 2% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0031] According to some embodiments of the present invention, the mass of polyvinyl butyral accounts for 8 to 10% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0032] According to some embodiments of the present invention, the mass of polyvinyl butyral accounts for any one of 8%, 8.5%, 9%, 9.5%, 10% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide, and bismuth oxide, or a range of any two, such as 8 to 10%.

[0033] According to some embodiments of the present invention, the mass of polyvinyl butyral accounts for 9% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0034] According to some embodiments of the present invention, the mass of dibutyl phthalate accounts for 9 to 12% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0035] According to some embodiments of the present invention, the mass of dibutyl phthalate accounts for any one of 9%, 10%, 11%, or 12% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide, and bismuth oxide, or a range of any two, such as 10 to 12%.

[0036] According to some embodiments of the present invention, the mass of dibutyl phthalate accounts for 10% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0037] According to some embodiments of the present invention, the solvent is anhydrous ethanol, wherein the mass of the solvent accounts for 50-70% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0038] According to some embodiments of the present invention, the solvent is anhydrous ethanol, wherein the mass of the solvent accounts for any value or a range of any two of 55%, 60%, 65%, 70% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide, such as 60~65%.

[0039] According to some embodiments of the present invention, the solvent is anhydrous ethanol, wherein the mass of the solvent accounts for 60% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0040] According to some embodiments of the present invention, a double scraper can be used during tape casting. The height of the double scraper needs to be controlled. If it is too low, it will increase the degree of orientation of the template grains, but the increase is limited and the scraping efficiency is not high. If it is too high, it will reduce the degree of orientation of the template grains, reduce the texture of the ceramic, and cause the piezoelectric properties to deteriorate.

[0041] According to some embodiments of the present invention, the stacking method includes: bonding and pressing two single-layer cast films at 80°C to make them fit tightly together, and repeating the operation to stack multiple cast films to a thickness of 2-3 mm.

[0042] According to some embodiments of the present invention, the hot pressing includes: hot pressing at 60~80°C and 50~60MPa for 15~20 minutes.

[0043] According to some embodiments of the present invention, the glue removal process includes: heating to 240°C for 120 minutes at room temperature, heating to 350°C for 270 minutes, heating to 600°C for 500 minutes, holding at that temperature for 80 minutes, and then cooling with the furnace.

[0044] According to some embodiments of the present invention, the first cold isostatic pressing includes: holding the pressure at 200~250MPa for 5~10min; and / or, the second cold isostatic pressing includes: holding the pressure at 200~250MPa for 5~10min.

[0045] According to some embodiments of the present invention, the sintering includes: heating to 1150°C at a rate of 3~5°C / min and holding at that temperature for 8 hours.

[0046] According to some embodiments of the present invention, sintering is carried out using a double-layer alumina crucible and a method of embedding homogeneous powder.

[0047] According to some embodiments of the present invention, bismuth oxide, titanium dioxide, potassium chloride and anhydrous ethanol are placed in a ball mill jar and ball milled for 4 hours at a speed of 300 r / min using a planetary ball mill. The mixed powder is dried, then placed in a crucible and calcined in a muffle furnace, heated to 1140°C at a rate of 5°C / min and held at that temperature for 8 hours.

[0048] According to some embodiments of the present invention, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide, bismuth oxide, additives and solvent are mixed and ball-milled at 300 r / min for 12 h. Bismuth titanate template grains are added and ball-milled at 250 r / min for 12 h to obtain a ceramic slurry.

[0049] According to some embodiments of the present invention, a defoaming machine is used to defoam the ceramic slurry. Then, a plastic film is laid on the casting substrate. After assembling the double-scraper device, the material tank and scraper device are placed, and the height of the double scrapers is set using a micrometer. The first scraper performs a first casting of the slurry, initially spreading it evenly on the casting substrate at a distance of 500 μm. The second scraper performs a second casting of the spread slurry, aiming to make the final single-layer cast film smoother and the grains more evenly arranged; the second scraper is also 500 μm away from the casting substrate. The drying device of the casting machine is turned on and set to 50°C. A suitable initial speed is set, and the casting slurry is poured into the material tank. After all the slurry is poured into the tank, the forward rotation of the casting machine is started, spreading the slurry evenly on the casting film substrate. After casting, wait 5-10 minutes for the solvent in the cast film to dry, resulting in a single-layer cast film with a thickness of approximately 40 μm.

[0050] Lamination involves bonding two single-layer cast films together at 70-80℃ and applying pressure to ensure tight adhesion. This process is repeated until multiple cast films are laminated to a thickness of 2-3 mm. Then, the films are hot-pressed at 60-80℃ and 50-60 MPa for 15-20 minutes, followed by a cold isostatic pressing at 200-250 MPa for 5-10 minutes to obtain the cast film sheet. The purpose is to achieve a tighter bond between the cast films and improve their density.

[0051] According to some embodiments of the present invention, bismuth oxide is 3% of the molar fraction of the bismuth titanate template crystal.

[0052] According to some embodiments of the present invention, after sintering, both sides of the ceramic sample are polished, silvered, and polarized. After polarization, a textured ceramic that can be tested is obtained. Attached Figure Description

[0053] Figure 1 Bi₄Ti₃O₃ sintered at 1140℃ for 8 hours in a pure salt KCl system 12 XRD diffraction pattern of template grains.

[0054] Figure 2 The modified textured ceramic-Sr prepared in Example 1 0.04 Ta 0.006 Randomly oriented ceramics -Sr prepared in Comparative Example 2 0.04 Ta 0.006 The XRD diffraction pattern.

[0055] Figure 3 Unmodified textured ceramics -Sr prepared in Comparative Example 1 0.04 Ta 0.006 Randomly oriented ceramics -Sr prepared in Comparative Example 2 0.04 Ta 0.006 The XRD diffraction pattern.

[0056] Figure 4 Bi₄Ti₃O₃ sintered at 1140℃ for 8 hours in a pure salt KCl system 12 Scanning electron microscope (SEM) image of the template grains.

[0057] Figure 5 Bi₄Ti₃O₃ sintered at 1100℃ for 2 hours in a mixed salt NaCl-KCl system 12 Scanning electron microscope (SEM) image of the template grains.

[0058] Figure 6 This is a microscopic morphology image of the cross-section of the textured ceramic prepared in Example 1.

[0059] Figure 7 The modified textured ceramic-Sr prepared in Example 10.04 Ta 0.006 The electro-strain curve.

[0060] Figure 8 Unmodified textured ceramics -Sr prepared in Comparative Example 1 0.04 Ta 0.006 The electro-strain curve. Detailed Implementation

[0061] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0062] In a first aspect, some embodiments of the present invention provide a sodium bismuth titanate-based lead-free piezoelectric textured ceramic with the chemical composition [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 1x Ta x O3, 0< x <0.01, the texture of sodium bismuth titanate-based lead-free piezoelectric textured ceramics is >90%.

[0063] It should be noted that the sodium bismuth titanate-based lead-free piezoelectric textured ceramic of the present invention has highly oriented grains. The high orientation of the grains is beneficial to greatly improving its remanent polarization intensity, thereby improving the piezoelectric performance. It is an anisotropic piezoelectric ceramic with excellent piezoelectric performance.

[0064] In conjunction with the first aspect, in some embodiments of the present invention, the textured ceramic grains of the sodium bismuth titanate-based lead-free piezoelectric textured ceramic are along... <001> orientation.

[0065] It should be noted that the textured ceramic grains of lead-free piezoelectric textured ceramics are along... <001> With orientation and a texture degree greater than 90%, it has the following important beneficial effects:

[0066] 1. Enhanced piezoelectric properties:

[0067] <001> Oriented grain arrangement can significantly improve the piezoelectric response of materials, typically exhibiting a significantly increased piezoelectric coefficient (d33). The piezoelectric effect is usually closely related to grain orientation, especially along the grain direction. <001> Oriented grains can optimize the polarization effect of materials, thereby improving their piezoelectric properties. Well-oriented materials can effectively convert mechanical energy into electrical energy (reverse piezoelectric effect) or electrical energy into mechanical energy (forward piezoelectric effect).

[0068] Due to the high texture (>90%), most grains are oriented in the same direction, which will further improve the output of the piezoelectric effect, enhance the piezoelectric coefficient of the material, and make it more efficient in practical applications.

[0069] 2. Improved the mechanical properties of the material:

[0070] High texture typically means that the grains within the material are highly uniformly oriented. This structure not only improves piezoelectric properties but also enhances the material's mechanical strength and toughness. Ceramic materials with high texture generally exhibit better crack resistance and deformation resistance than non-textured materials. The uniform grain structure of textured ceramics contributes to the material's durability and stability during use, particularly demonstrating excellent mechanical properties under high loads and long-term use.

[0071] 3. Improved motor conversion efficiency:

[0072] Due to the directional preference of textured ceramic grains ( <001> This orientation allows the electric field to propagate more effectively between grains, enhancing the material's electromechanical conversion efficiency. This is crucial for piezoelectric applications requiring high-efficiency energy conversion, such as sensors and actuators. Furthermore, this orientation can optimize the polarization behavior of piezoelectric ceramics under an electric field, thereby improving their power density and response speed in practical applications.

[0073] 4. The stability and consistency of the material have been optimized:

[0074] High texture ensures the uniformity of the material's crystal structure, which is crucial for its long-term stability. Textured ceramics can maintain stable performance and avoid performance degradation under environmental changes such as temperature fluctuations, external stress, or electric field variations. The strong grain orientation of textured ceramics can effectively reduce the influence of grain boundary defects, thereby improving the material's consistency and reliability.

[0075] 5. Reduced energy loss and improved high-temperature resistance:

[0076] <001> Oriented grains enable ceramics to respond more precisely and efficiently to an applied electric field, allowing the material to efficiently convert external energy. High texture helps reduce internal defects and domain wall movement, thereby reducing dielectric loss. They typically exhibit good stability at high temperatures; therefore, well-oriented ceramics can maintain their piezoelectric properties at high temperatures, making them suitable for applications in high-temperature or complex environments.

[0077] These effects enable the material to exhibit excellent performance in piezoelectric applications such as sensors, actuators, energy harvesting, and acoustic devices, while also meeting the requirements of sustainable development.

[0078] In conjunction with the first aspect, in some embodiments of the present invention, x is 0.006, and the chemical composition of the sodium bismuth titanate-based lead-free piezoelectric textured ceramic is [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 O3.

[0079] [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 O3 lead-free piezoelectric textured ceramics exhibit high electrostrain performance among randomly oriented ceramics, thus textured ceramics can be used to further improve their properties.

[0080] In a second aspect, some embodiments of the present invention provide a method for preparing sodium bismuth titanate-based lead-free piezoelectric textured ceramics according to the first aspect of the present invention, comprising the following steps:

[0081] Bismuth titanate template crystals were prepared using a single molten salt system. Based on the chemical composition, bismuth titanate template crystals, titanium dioxide, sodium carbonate, potassium carbonate, strontium carbonate, and tantalum pentoxide were weighed and mixed with bismuth oxide, additives, and solvents to obtain a ceramic slurry. The ceramic slurry was then cast using a reactive template grain growth method and a casting process to obtain a single-layer cast film. The single-layer cast films were stacked to obtain a cast film sheet. The cast film sheet was then subjected to hot pressing, a first cold isostatic pressing, debinding, a second cold isostatic pressing, and sintering to obtain the sodium bismuth titanate-based lead-free piezoelectric textured ceramic of the present invention.

[0082] When preparing piezoelectric textured ceramics with high electrostriction, researchers often use a sodium chloride-potassium chloride (NaCl-KCl) composite molten salt system to prepare bismuth titanate template grains via the molten salt method. This results in grains of varying sizes, and the high preparation temperature leads to the presence of impurity phases within the template grains, affecting the stoichiometry of the textured ceramic. Consequently, the final bismuth titanate template grains are relatively small in orientation, contain impurity phases, and have a large size range, making it impossible to prepare high-purity, large-size sheet-like bismuth titanate template grains. To obtain high-purity lead-free piezoelectric ceramics that can improve electrical properties through doping modification while maintaining high texture and density, further optimization of the preparation process is urgently needed. This invention is based on further improving BNKT (Bi 0.5 Na 0.84 K 0.16 ) 0.5TiO3-0.45(Bi 0.1 Sr 0.85 The piezoelectric properties of TiO3-based ceramics were improved by co-doping of A-site and B-site ions in a binary solid solution of sodium bismuth titanate-potassium bismuth titanate (BNT-BKT). Using a single molten salt system combined with texturing technology (reactive template grain growth method), the ceramic crystal structure was altered using suitable templates and tape casting processes, resulting in an ordered arrangement of ceramic grains and thus obtaining anisotropic piezoelectric ceramics with excellent piezoelectric properties. This can provide a reference for the industry in preparing templated and textured ceramics, further promoting the practical application of lead-free piezoelectric ceramics.

[0083] It is understood that the preparation method of this invention uses sheet-like doped bismuth titanate with the same composition as the doped sodium bismuth titanate ceramic powder as a template. Since the reaction template grain growth method involves mixing the template and the drug powder together, stacking them, and then sintering, during the sintering process, the template grains engulf the surrounding drug powder and participate in the reaction. Therefore, the identical composition avoids the internal stress caused by different lattice constants that would result after the template grains engulf the surrounding drug powder particles and participate in the reaction, thus preventing the internal stress from affecting the piezoelectric properties.

[0084] The preparation method of the present invention is simple, easy to operate, and low in cost, which can save experimental costs and equipment investment.

[0085] In conjunction with the second aspect, in some embodiments of the present invention, the bismuth titanate template crystal is plate-shaped and has the chemical formula Bi₄Ti₃O₃. 12 .

[0086] Bismuth titanate template crystals are plate-like, which can bring a series of beneficial effects to ceramic materials, specifically the following advantages:

[0087] The lamellar template grains provide a preferred orientation, causing the sodium bismuth titanate-based ceramic crystals to grow along the direction of the lamellar template grains during subsequent synthesis. This helps improve the grain orientation of the ceramic and significantly enhances the texture of the final textured ceramic. For sodium bismuth titanate-based ceramics, the highly textured microstructure formed by the lamellar template grains usually results in better electrical properties, such as higher dielectric constant, lower dielectric loss, and stronger piezoelectric response. These are all important characteristics sought after by high-performance electronic components.

[0088] The presence of lamellar template grains can guide crystal growth along specific directions, reducing microcracks and other internal defects caused by random orientation, and improving the overall mechanical strength of the material. By utilizing lamellar template grains, the particle size and spatial distribution in the final ceramic material can be better controlled, thereby obtaining textured ceramics with better density and smoothness.

[0089] In conjunction with the second aspect, in some embodiments of the present invention, the method for preparing bismuth titanate template crystals includes the following steps: mixing Bi2O3 and TiO2, adding a single molten salt, and then ball milling, drying and calcining to obtain bismuth titanate template crystals.

[0090] According to some embodiments of the present invention, the single molten salt is a KCl molten salt system.

[0091] Compared to a single NaCl system, the KCl system produces templates with higher crystallinity and purity. Figure 1 The XRD pattern also shows that the diffraction peaks in the BiT template grains prepared using the KCl molten salt system are completely consistent with those of BiT in the standard PDF card PDF#72-1019. Meanwhile, the NaCl molten salt contains Na... + As an impurity, it enters the BiT crystal and readily forms Na with Bi₂O₃ and TiO₂. 0.5 Bi 4.5 Ti4O 15 Then Bi4Ti3O 12 The three-layered TiO6 oxygen octahedron and Na 0.5 Bi 4.5 Ti4O 15 The four-layered TiO6 oxygen octahedron in (Bi2O2) 2+ The alternating layers form a superlattice structure, creating a symbiotic relationship between BiT and Na. 0.5 Bi 8.5 Ti7O 27 This results in low purity of the prepared BiT template, making it difficult to calculate the specific phase content. Furthermore, the stoichiometry of the prepared textured ceramics deviates, affecting the sample's performance. Therefore, this invention selects a KCl molten salt system to prepare BiT template grains.

[0092] According to some embodiments of the present invention, the preparation method of bismuth titanate template crystal may be as follows:

[0093] First, react Bi₂O₃ and TiO₂ according to the chemical reaction equation: 2Bi₂O₃ + 3TiO₂ → Bi₄Ti₃O 12 Formula calculations were performed, and bismuth oxide and titanium dioxide were weighed and mixed according to the molar ratio. A single potassium chloride (KCl) molten salt was selected as the molten salt system. The mass ratio of molten salt (KCl) to the reaction raw materials (Bi2O3 and TiO2) can be 1.5:1.

[0094] After weighing, the sample was placed in a ball mill jar and mixed for 4 hours at 300 rpm using zirconia balls and anhydrous ethanol as solvent in a planetary ball mill. The resulting slurry was dried at 80°C. The dried powder was then placed in a corundum crucible, sealed with the crucible lid, and placed in a muffle furnace for synthesis to prevent the large-scale volatilization of molten salt and Bi at high temperatures. The synthesis process involved heating to 1140°C at room temperature at a heating rate of 5°C / min and holding for 8 hours, followed by cooling to 300°C at a rate of 3°C / min and then cooling with the furnace. The synthesized powder was then added to deionized water at 80-100°C and stirred, dispersed, and washed multiple times. After discarding the supernatant, the powder in the beaker was finally dried to obtain flake-like Bi₄Ti₃O₃ prepared in a pure KCl system. 12 Template grains.

[0095] In conjunction with the second aspect, in some embodiments of the present invention, the additives include polyvinyl butyral, dibutyl phthalate, polyethylene glycol, and castor oil.

[0096] The role of polyvinyl butyral is as a binder, forming a network structure in the slurry to bind ceramic powder particles together, increasing the slurry viscosity, ensuring the uniformity of the slurry throughout the processing, and contributing to the preparation of a smooth cast film. Simultaneously, it provides the necessary mechanical strength to the green body, making it less prone to breakage and ensuring the dimensional accuracy of the ceramic sheets.

[0097] Dibutyl phthalate (DBP) acts as a plasticizer, preventing powder particle agglomeration and maintaining the stability of the slurry. DBP weakens intermolecular forces by intercalating between polymer chains, giving the slurry good flowability and processability even at lower temperatures.

[0098] Polyethylene glycol (PEG) acts as a plasticizer, increasing the fluidity of the slurry by reducing its viscosity. This makes the slurry suitable for casting and easier to spread into a uniform thin layer. It also has a lubricating effect, helping the cast film and green body to detach smoothly from the mold or carrier, reducing the risk of breakage during demolding. PEG has a slow evaporation rate, providing a longer time window before sintering to maintain its plasticizing effect. Furthermore, it decomposes more easily and completely during high-temperature sintering, leaving no harmful residues and making it more environmentally friendly.

[0099] Castor oil acts as a dispersant. During the preparation of casting slurries, powder particles are prone to agglomeration, which affects the uniformity of the slurry and the final properties of the textured ceramic. Castor oil can adsorb onto the particle surface, altering the particle surface properties and reducing the attractive force between particles, thereby preventing agglomeration. Simultaneously, it helps maintain the stable suspension of ceramic powder in the solvent, increasing the viscosity of the slurry and making the particles less prone to sedimentation or stratification.

[0100] In conjunction with the second aspect, in some embodiments of the present invention, castor oil accounts for 2% of the total mass, polyvinyl butyral accounts for 9% of the total mass, and dibutyl phthalate accounts for 10% of the total mass.

[0101] In conjunction with the second aspect, in some embodiments of the present invention, the solvent is anhydrous ethanol, wherein the mass of the solvent accounts for 60% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide and bismuth oxide.

[0102] In conjunction with the second aspect, in some embodiments of the present invention, a double scraper can be used during the casting process. The height of the double scraper needs to be controlled. If it is too low, it will increase the degree of orientation of the template grains, but the increase is limited and the scraping efficiency is not high. If it is too high, it will reduce the degree of orientation of the template grains, reduce the texture of the ceramic, and cause the piezoelectric properties to deteriorate.

[0103] In conjunction with the second aspect, in some embodiments of the present invention, the stacking method includes: bonding and pressing two single-layer cast films at 80°C to make them tightly bonded, and repeating the operation to stack multiple cast films to a thickness of 2-3 mm.

[0104] In conjunction with the second aspect, in some embodiments of the present invention, hot pressing includes: hot pressing at 70°C and 60 MPa for 20 minutes.

[0105] In conjunction with the second aspect, in some embodiments of the present invention, the glue removal process includes: heating to 240°C for 120 minutes at room temperature, heating to 350°C for 270 minutes, heating to 600°C for 500 minutes, holding at that temperature for 80 minutes, and then cooling with the furnace.

[0106] In conjunction with the second aspect, in some embodiments of the present invention, a single cold isostatic pressing includes: holding at 200 MPa for 5 minutes.

[0107] In conjunction with the second aspect, in some embodiments of the present invention, the secondary cold isostatic pressing includes: holding at a pressure of 200~250MPa for 5~10 minutes.

[0108] In conjunction with the second aspect, in some embodiments of the present invention, sintering includes: heating to 1150°C at a rate of 5°C / min and holding at that temperature for 8 hours.

[0109] In conjunction with the second aspect, in some embodiments of the present invention, sintering is carried out using a double-layer alumina crucible and a method of embedding homogeneous powder.

[0110] In conjunction with the second aspect, in some embodiments of the present invention, bismuth oxide, titanium dioxide, potassium chloride and anhydrous ethanol are placed in a ball mill jar and ball milled for 4 hours at a speed of 300 r / min using a planetary ball mill. The mixed powder is then dried, placed in a crucible and calcined in a muffle furnace, heated to 1140°C at a rate of 5°C / min and held at that temperature for 8 hours.

[0111] In conjunction with the second aspect, in some embodiments of the present invention, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide, bismuth oxide, additives and solvent are mixed and ball-milled at 300 r / min for 12 h, bismuth titanate template grains are added, and ball-milled at 250 r / min for 12 h to obtain a ceramic slurry.

[0112] In conjunction with the second aspect, in some embodiments of the present invention, a defoaming machine is used to defoam the ceramic slurry. Then, a plastic film is laid on the casting substrate. After assembling the double-scraper device, the material tank and scraper device are placed, and the height of the double scrapers is set using a micrometer. The first scraper performs a first casting of the slurry, initially spreading it evenly on the casting substrate at a distance of 500 μm. The second scraper performs a second casting of the spread slurry, aiming to make the final single-layer cast film smoother and the grains more evenly arranged; the second scraper is also 500 μm away from the casting substrate. The drying device of the casting machine is set to 50°C, and a suitable initial speed is set. The casting slurry is then poured into the material tank. After all the slurry is poured into the tank, the forward rotation of the casting forming machine is started, spreading the slurry evenly on the casting film substrate. After casting, wait 5-10 minutes for the solvent in the cast film to dry, resulting in a single-layer cast film with a thickness of approximately 40 μm.

[0113] Lamination involves bonding two single-layer cast films together at 80°C under pressure to ensure tight adhesion. This process is repeated until multiple cast films are laminated to a thickness of 2-3 mm. The laminates are then hot-pressed at 70°C and 60 MPa for 20 minutes, followed by a cold isostatic pressing at 200 MPa for 5 minutes to obtain the cast film sheet. The purpose is to achieve a tighter bond between the cast films and improve their density.

[0114] In conjunction with the second aspect, in some embodiments of the present invention, bismuth oxide is 3% of the molar fraction of the bismuth titanate template crystal.

[0115] In some comparative embodiments, the preparation method of the unmodified sodium bismuth titanate-based lead-free piezoelectric textured ceramic may be:

[0116] Using bismuth oxide (Bi₂O₃) and titanium dioxide (TiO₂) as raw materials, plate-like Bi₄Ti₃O₃ was synthesized by the molten salt method. 12 The template crystal has the following reaction equation:

[0117] 2Bi₂O₃ + 3TiO₂ → Bi₄Ti₃O12 .

[0118] Bismuth oxide and titanium dioxide are weighed and mixed in a molar ratio of 2:3.

[0119] The molten salt system used was a mixed molten salt of NaCl and KCl, with a mass ratio of molten salt (NaCl and KCl) to reactants (Bi₂O₃ and TiO₂) of 1.5:1. Sodium chloride (NaCl) and potassium chloride (KCl) were dried in an oven for 24 hours before weighing. After mixing the raw materials, the mixture underwent ball milling, drying, and calcination to obtain bismuth titanate template crystals.

[0120] Bismuth oxide, titanium dioxide, sodium chloride, potassium chloride, and anhydrous ethanol were placed in a ball mill jar and ball milled for 4 hours at 300 r / min using a planetary ball mill. The mixed powder was dried, then placed in a crucible and calcined in a muffle furnace. The temperature was increased to 1100℃ at a rate of 5℃ / min and held for 2 hours.

[0121] Bismuth oxide is 3% of the molar fraction of the bismuth titanate template crystal.

[0122] The additives include polyvinyl butyral, dibutyl phthalate, polyethylene glycol, and castor oil. The solvent is anhydrous ethanol. The solvent accounts for 60% of the total mass of the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide, and bismuth oxide. Castor oil accounts for 2% of the total mass, polyvinyl butyral accounts for 9% of the total mass, and dibutyl phthalate accounts for 10% of the total mass.

[0123] Titanium dioxide, sodium carbonate, potassium carbonate, tantalum pentoxide, bismuth oxide, additives and solvents are mixed and ball-milled at 300 r / min for 12 h. Bismuth titanate template grains are added and ball-milled at 250 r / min for 1-2 h to obtain a mixed slurry.

[0124] Defoaming is performed on the mixed slurry using a defoamer. A plastic film is then laid on the casting substrate. After assembling the casting doctor blade assembly, the material trough and doctor blade assembly are placed, and the doctor blade height is set using a micrometer. The distance between the doctor blade and the casting substrate is 150 μm. The drying device of the casting machine is turned on and set to 50℃. A suitable initial speed of the casting machine is set, and the casting slurry is poured into the material trough. After all the slurry is poured into the trough, the forward rotation of the casting machine is started, allowing the slurry to spread evenly on the casting film substrate. After casting, wait 5-10 minutes for the solvent in the cast film to dry, resulting in a single-layer cast film with a thickness of approximately 40 μm.

[0125] Lamination involves bonding two single-layer cast films together at 80°C under pressure to ensure tight adhesion. This process is repeated until multiple cast films are laminated to a thickness of 2-3 mm. The laminates are then hot-pressed at 70°C and 60 MPa for 20 minutes, followed by a cold isostatic pressing at 200 MPa for 5 minutes to obtain the cast film sheet. The purpose is to achieve a tighter bond between the cast films and improve their density.

[0126] The debinding process involves heating from room temperature to 240℃ for 120 minutes, then to 350℃ for 270 minutes, and finally to 600℃ for 500 minutes. After holding at this temperature for 80 minutes, the temperature is cooled in the furnace. The cold isostatic pressing is performed at a pressure of 200-250 MPa for 5-10 minutes, resulting in a green compact after the second cold isostatic pressing.

[0127] Sintering was carried out using a double-layer alumina crucible and a homogeneous powder sintering method. The program was to heat the material to 1150℃ at a rate of 5℃ / min and then hold it at that temperature for 8 hours.

[0128] The preparation of sodium bismuth titanate-based lead-free piezoelectric randomly oriented ceramics, compared to sodium bismuth titanate-based lead-free piezoelectric textured ceramics, can be as follows:

[0129] Using the traditional solid-phase method, based on the chemical ratio [Bi] 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 O3 was prepared by weighing bismuth dioxide (Bi2O3), titanium dioxide (TiO2), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), strontium carbonate (SrCO3), and tantalum pentoxide (Ta2O5) as raw materials, and then successively mixing, ball milling, drying, pre-firing, secondary ball milling, and secondary drying to obtain ceramic powder. A binder was added to the powder for granulation, and after preliminary pressing in a mold, the sample was compacted by isostatic pressing, followed by debinding and sintering. After cooling, sodium bismuth titanate-based lead-free piezoelectric randomly oriented ceramic was obtained.

[0130] Bismuth dioxide, titanium dioxide, sodium carbonate, potassium carbonate, strontium carbonate, tantalum pentoxide, and a solvent were placed in a ball mill jar and ball-milled for 4 hours at 300 rpm using a planetary ball mill to obtain a slurry. The solvent was anhydrous ethanol.

[0131] The slurry was dried, then placed in a crucible and preheated in a muffle furnace. The temperature was increased to 850°C at a rate of 5°C / min and held for 3 hours.

[0132] The pre-fired ceramic powder and solvent were placed in a ball mill jar and ball milled for 4 hours at a speed of 300 r / min using a planetary ball mill. The mixture was then dried and sieved.

[0133] The powder after secondary ball milling was granulated by adding 6 wt.% PVB alcohol solution as a binder. The granulated powder was then compressed into tablets using a 10 mm diameter mold and tablet press. The isostatic pressing process involved increasing the pressure to 200 MPa over 5 minutes, holding the pressure for 5 minutes, and then decreasing the pressure.

[0134] Sintering was carried out using a double-layer alumina crucible and a homogeneous powder sintering method. The program was to heat the material to 1150℃ at a rate of 5℃ / min and then hold it at that temperature for 3 hours.

[0135] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0136] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0137] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0138] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0139] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0140] Example 1

[0141] A sodium bismuth titanate-based lead-free piezoelectric textured ceramic is provided, and its preparation method is as follows:

[0142] Step 1: Preparation of bismuth titanate template grains:

[0143] First, react Bi₂O₃ and TiO₂ according to the chemical reaction equation: 2Bi₂O₃ + 3TiO₂ → Bi₄Ti₃O 12Formula calculations were performed, and bismuth oxide and titanium dioxide were weighed and mixed in a molar ratio of 2:3. A single potassium chloride (KCl) molten salt was selected as the molten salt system, and the mass ratio of molten salt (KCl) to the reaction raw materials (Bi2O3 and TiO2) was 1.5:1.

[0144] After weighing, the sample was placed in a ball mill jar and mixed for 4 hours at 300 rpm using zirconia balls and anhydrous ethanol as solvent in a planetary ball mill. The resulting slurry was dried at 80°C. The dried powder was then placed in a corundum crucible, sealed with the crucible lid, and placed in a muffle furnace for synthesis to prevent the large-scale volatilization of molten salt and Bi at high temperatures. The synthesis process involved heating to 1140°C at room temperature at a heating rate of 5°C / min and holding for 8 hours, followed by cooling to 300°C at a rate of 3°C / min and then cooling with the furnace. The synthesized powder was then mixed with deionized water at 80-100°C and stirred, dispersed, and washed multiple times. After discarding the supernatant, the powder in the beaker was finally dried to obtain flake-like Bi₄Ti₃O₃ prepared in a pure KCl system. 12 Template grains.

[0145] Step 2: Preparation of sodium bismuth titanate-based lead-free piezoelectric textured ceramics with high electrostrain performance. The specific steps are as follows:

[0146] (1) Mixing

[0147] The required Bi4Ti3O 12 Template grains, titanium dioxide (TiO2), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), strontium carbonate (SrCO3), and tantalum pentoxide (Ta2O5) were placed in an oven and dried at 150℃ for 2 hours, according to the chemical formula [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 The stoichiometric ratio of O3 was determined by weighing the raw materials, namely Bi:Na:K:Ti:Sr:Ta = 0.48:0.3936:0.0864:0.994:0.04:0.006, and the amount of substance was determined to be Bi4Ti3O. 12 Template grains and an excess of 3% bismuth oxide (Bi₂O₃). Except for the BiT template grains, all other powders were placed in a nylon ball mill jar. Using zirconia balls as milling balls and anhydrous ethanol as solvent, the mixture was ball-milled at 300 rpm for 4 hours. Afterward, Bi₄Ti₃O₃ was added. 124wt% castor oil (2% by total mass of TiO2, Na2CO3, K2CO3, Ta2O5, SrCO3, and Bi2O3) was added, along with 48wt% polyvinyl butyral (PVB) (9% by total mass) and 40wt% dibutyl phthalate (DBP) (10% by total mass). Solvent was then added again, with the total mass of solvent added in both steps being Bi4Ti3O3. 12 The total mass of TiO2, Na2CO3, K2CO3, Ta2O5, SrCO3, and Bi2O3 was 60%, and the mixture was ball-milled in a planetary ball mill at 300 r / min for 12 h. The resulting preliminary slurry was transferred into a beaker through a pipette, and the beaker was stirred on a magnetic stirrer. Then, the flake-like Bi4Ti3O3 prepared in the pure KCl system in step 1 was added. 12 Template grains are removed, and the slurry is stirred at room temperature for 1-2 hours to obtain a mixed slurry.

[0148] (2) Casting

[0149] The mixed slurry is defoamed using a defoamer until it becomes viscous. A plastic film is then laid on the casting substrate. After assembling the double-scraper device, the material trough and scraper device are placed, and the height of the double scrapers is set using a micrometer. The distance between the front scraper and the casting substrate is 500 μm. The distance between the rear scraper and the casting substrate is also 500 μm, and the distance between the front and rear scrapers is 3 cm. The drying device of the casting machine is turned on and set to 50℃. The initial speed of the casting machine is set to 0.2 m / min. The casting slurry is then poured into the material trough. After all the slurry is poured into the trough, the forward rotation of the casting machine is started, allowing the slurry to spread evenly on the casting film substrate. After casting, wait 5-10 minutes for the solvent in the cast film to dry, resulting in a single-layer cast film with a thickness of approximately 40 μm.

[0150] (3) Stacking

[0151] Cut the cast film to the appropriate size using a paper cutter. Heat the hot press to 80°C and press the two single-layer cast films together with the sides without plastic film on them. Apply pressure with the hot press to make them stick together tightly. Peel off the top plastic film and press it together with the side without plastic film on another cast film. Repeat the operation to stack the cast films to a thickness of 2-3mm to obtain a cast film stack.

[0152] (4) Hot pressing, one-time cold isostatic pressing

[0153] The cast film stack was hot-pressed at 70℃ and 60MPa for 15 minutes to make the layers in the green compact more compact. After being removed and allowed to cool naturally, it was vacuum-sealed and then placed in a cold isostatic press for a cold isostatic pressing treatment, holding the sample at 200MPa for 5 minutes.

[0154] (4) Degreasing and cold isostatic pressing

[0155] After hot pressing and cold isostatic pressing, the green preforms are cut into 7mm × 7mm square pieces and evenly placed on an alumina plate, then pressed down with another alumina plate. The samples are placed in a debinding furnace, where the debinding process involves heating from room temperature to 240℃ for 120 minutes, then to 350℃ for 270 minutes, and finally to 600℃ for 500 minutes, holding at that temperature for 80 minutes before cooling in the furnace. After the cast film stack has cooled naturally, the pieces are vacuum-sealed and placed in a cold isostatic press for a second cold isostatic pressing treatment, holding the samples at 200MPa for 5 minutes.

[0156] (6) Sintering

[0157] Sintering was performed using a double-layer alumina crucible and a homogeneous powder embedding method. The debinded green body was placed in the crucible for sintering. The program involved heating to 1150℃ at a rate of 5℃ / min and holding for 8 hours to obtain sodium bismuth titanate-based lead-free piezoelectric textured ceramics with the chemical formula [Bi]. 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 O3, and named textured ceramics-Sr 0.04 Ta 0.006 .

[0158] (7) Polishing, ultrasonication, silver plating, and silver infiltration

[0159] After removal, both sides of the sample need to be polished to remove the ceramic surface layer. The ceramic thickness should be ground to 0.6-0.8 mm using 600-grit and 800-grit diamond sandpaper. The polished ceramic surface should not be too smooth or too rough. After polishing, the sample is ultrasonically cleaned, removed, and dried before silver plating. Silver plating involves coating the ceramic surface with a layer of silver paste as an electrode, preparing for polarization and performance testing. After drying, the silver paste is evenly applied to both sides of the sample using screen printing technology. After drying on a heating platform, the sample is placed in a box furnace for silver infiltration. The silver infiltration program involves holding at 720℃ for 15 minutes.

[0160] (8) Polarization

[0161] Before polarization, the silver paste on the edges of the ceramic sheet needs to be polished away, leaving only the silver paste on the top and bottom surfaces to prevent short circuits caused by the silver paste at the edges during polarization. Polarization is performed in a silicone oil bath, and the polarization stage consists of a high-voltage DC power supply and a constant-temperature oil bath. Before polarization, the thickness of the ceramic sheet is measured, and the required polarization voltage is calculated using an electric field strength parameter of 3 kV / mm. The voltage is slowly increased to the required level and held for 10 minutes to allow the ceramic sheet to be fully polarized. If a sudden change in leakage current occurs during polarization, accompanied by sparks, it indicates that the edges of the ceramic sheet are conductive or the middle is broken down. The conductive edges or broken parts of the sample need to be polished away, and then repolarized. After polarization, a textured ceramic-Sr suitable for testing is obtained. 0.04 Ta 0.006 .

[0162] Comparative Example 1

[0163] An unmodified sodium bismuth titanate-based lead-free piezoelectric textured ceramic is provided, and its preparation method is as follows:

[0164] Step 1: Preparation of bismuth titanate template grains:

[0165] First, react Bi₂O₃ and TiO₂ according to the chemical reaction equation: 2Bi₂O₃ + 3TiO₂ → Bi₄Ti₃O 12 Formula calculations were performed, and bismuth oxide and titanium dioxide were weighed and mixed at a molar ratio of 2:3. A mixed molten salt of sodium chloride (NaCl) and potassium chloride (KCl) was selected, with a mass ratio of molten salt (NaCl and KCl) to reactants (Bi₂O₃ and TiO₂) of 1.5:1. After weighing, the mixture was placed in a ball mill jar, using zirconia balls as grinding media and anhydrous ethanol as solvent, and mixed at 300 r / min for 4 h in a planetary ball mill. The resulting slurry was dried at 80 °C. The resulting powder was placed in a corundum crucible, sealed, and placed in a muffle furnace for synthesis to prevent the large-scale volatilization of molten salt and Bi element at high temperatures. The synthesis process involved heating at room temperature to 1100 °C at a heating rate of 5 °C / min and holding for 8 h, then cooling to 300 °C at a rate of 3 °C / min and then cooling with the furnace. The synthesized powder was then added to deionized water at 80-100 °C for stirring, dispersion, and washing multiple times. After discarding the supernatant, the powder in the beaker was finally dried to obtain flake-like Bi4Ti3O prepared in the NaCl-KCl system. 12 Template grains.

[0166] Step 2: Preparation of unmodified sodium bismuth titanate-based lead-free piezoelectric textured ceramics, the specific steps are as follows:

[0167] (1) Mixing

[0168] The required Bi4Ti3O 12Template grains, titanium dioxide (TiO2), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), strontium carbonate (SrCO3), and tantalum pentoxide (Ta2O5) were placed in an oven and dried at 150℃ for 2 hours, according to the chemical formula [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 The stoichiometric ratio of O3 was determined by weighing the raw materials, namely Bi:Na:K:Ti:Sr:Ta = 0.48:0.3936:0.0864:0.994:0.04:0.006, and the amount of substance was determined to be Bi4Ti3O. 12 Template grains and an excess of 3% bismuth oxide (Bi₂O₃). Except for the BiT template grains, all other powders were placed in a nylon ball mill jar. Using zirconia balls as milling balls and anhydrous ethanol as solvent, the mixture was ball-milled at 300 rpm for 4 hours. Afterward, Bi₄Ti₃O₃ was added. 12 4wt% castor oil (2% by total mass of TiO2, Na2CO3, K2CO3, Ta2O5, SrCO3, and Bi2O3) was added, along with 48wt% polyvinyl butyral (PVB) (9% by total mass) and 40wt% dibutyl phthalate (DBP) (10% by total mass). Solvent was then added again, with the total mass of solvent added in both steps being Bi4Ti3O3. 12 The total mass of TiO2, Na2CO3, K2CO3, Ta2O5, SrCO3, and Bi2O3 was 60%, and the mixture was ball-milled in a planetary ball mill at 300 r / min for 12 h. The resulting preliminary slurry was transferred into a beaker through a pipette, and the beaker was stirred on a magnetic stirrer. Then, the flake-like Bi4Ti3O3 prepared in the NaCl-KCl system in step 1 was added. 12 Template grains are removed, and the slurry is stirred at room temperature for 1-2 hours to obtain a mixed slurry.

[0169] (2) Casting

[0170] The mixed slurry is defoamed using a defoamer until it becomes viscous. A plastic film is then laid on the casting substrate. After assembling the individual doctor blade assembly, the material trough and doctor blade assembly are placed, and the height of the double doctor blades is set using a micrometer. The distance between the single doctor blade and the casting substrate is 150 μm. The drying device of the casting machine is turned on and set to 50℃. The initial speed of the casting machine is set to 0.2 m / min. The casting slurry is then poured into the material trough. After all the slurry has been poured into the trough, the forward rotation of the casting machine is started, allowing the slurry to spread evenly on the casting film substrate. After casting, wait 5-10 minutes for the solvent in the cast film to dry, resulting in a single-layer cast film with a thickness of approximately 40 μm.

[0171] (3) Stacking

[0172] Cut the cast film to the appropriate size using a paper cutter. Heat the hot press to 80°C and press the two single-layer cast films together with the sides without plastic film on them. Apply pressure with the hot press to make them stick together tightly. Peel off the top plastic film and press it together with the side without plastic film on another cast film. Repeat the operation to stack the cast films to a thickness of 2-3mm to obtain a cast film stack.

[0173] (4) Hot pressing, one-time cold isostatic pressing

[0174] The cast film stack was hot-pressed at 70℃ and 60MPa for 15 minutes to make the layers in the green compact more compact. After being removed and allowed to cool naturally, it was vacuum-sealed and then placed in a cold isostatic press for a cold isostatic pressing treatment, holding the sample at 200MPa for 5 minutes.

[0175] (4) Degreasing and cold isostatic pressing

[0176] After hot pressing and cold isostatic pressing, the green preforms are cut into 7mm × 7mm square pieces and evenly placed on an alumina plate, then pressed down with another alumina plate. The samples are placed in a debinding furnace, where the debinding process involves heating from room temperature to 240℃ for 120 minutes, then to 350℃ for 270 minutes, and finally to 600℃ for 500 minutes, holding at that temperature for 80 minutes before cooling in the furnace. After the cast film stack has cooled naturally, the pieces are vacuum-sealed and placed in a cold isostatic press for a second cold isostatic pressing treatment, holding the samples at 200MPa for 5 minutes.

[0177] (6) Sintering

[0178] Sintering was performed using a double-layer alumina crucible and a homogeneous powder embedding method. The debinded green body was placed in the crucible for sintering. The program involved heating to 1150℃ at a rate of 5℃ / min and holding for 8 hours to obtain sodium bismuth titanate-based lead-free piezoelectric textured ceramics with the chemical formula [Bi]. 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006 O3, and named it unmodified textured ceramic-Sr 0.04 Ta 0.006 .

[0179] (7) Polishing, ultrasonication, silver plating, and silver infiltration

[0180] After removal, both sides of the sample need to be polished to remove the ceramic surface layer. The ceramic thickness should be ground to 0.6-0.8 mm using 600-grit and 800-grit diamond sandpaper. The polished ceramic surface should not be too smooth or too rough. After polishing, the sample is ultrasonically cleaned, removed, and dried before silver plating. Silver plating involves coating the ceramic surface with a layer of silver paste as an electrode, preparing for polarization and performance testing. After drying, the silver paste is evenly applied to both sides of the sample using screen printing technology. After drying on a heating platform, the sample is placed in a box furnace for silver infiltration. The silver infiltration program involves holding at 720℃ for 15 minutes.

[0181] (8) Polarization

[0182] Before polarization, the silver paste on the edges of the ceramic sheet needs to be polished away, leaving only the silver paste on the top and bottom surfaces to prevent short circuits caused by the silver paste at the edges conducting during polarization. Polarization is performed in a silicone oil bath, and the polarization stage consists of a high-voltage DC power supply and a constant-temperature oil bath. Before polarization, the thickness of the ceramic sheet is measured, and the required polarization voltage is calculated using an electric field strength parameter of 3 kV / mm. The voltage is slowly increased to the required level and held for 10 minutes to allow the ceramic sheet to be fully polarized. If a sudden change in leakage current occurs during polarization, accompanied by sparks, it indicates that the edges of the ceramic sheet are conducting or the middle is broken down. The conducting edges or broken parts of the sample need to be polished away, and then repolarized. After polarization, unmodified textured ceramic-Sr is obtained for testing. 0.04 Ta 0.006 .

[0183] Comparative Example 2

[0184] A sodium bismuth titanate-based lead-free piezoelectric randomly oriented ceramic is provided, and its preparation method is as follows:

[0185] (1) Mixing powder, ball milling, and drying

[0186] Using bismuth dioxide (Bi₂O₃), titanium dioxide (TiO₂), sodium carbonate (Na₂CO₃), potassium carbonate (K₂CO₃), strontium carbonate (SrCO₃), and tantalum pentoxide (Ta₂O₅) as raw materials, according to the chemical formula [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 0.994 Ta 0.006The raw materials were weighed out according to the stoichiometric ratio of O3, namely Bi:Na:K:Ti:Sr:Ta = 0.48:0.3936:0.0864:0.994:0.04:0.006. Bi₂O₃, TiO₂, Na₂CO₃, K₂CO₃, SrCO₃, and Ta₂O₅ were mixed and anhydrous ethanol was added as the ball milling solvent. The mixture was ball-milled in a planetary ball mill at 300 rpm for 4 hours. After ball milling, the zirconium balls and slurry were poured into a ceramic dish and placed in an 80℃ oven for drying, while simultaneously opening the oven door to accelerate the evaporation of alcohol. After drying, the mixture of zirconium balls and pharmaceutical powder was passed through a 20-mesh sieve.

[0187] (2) Pre-firing

[0188] After sieving, the powder is placed in an alumina crucible and gently compacted. Then, it is placed in a muffle furnace and sintered at 850°C in air for 3 hours.

[0189] (3) Secondary ball milling and drying

[0190] The sintered powder was added to anhydrous ethanol and ball-milled for 4 hours in a planetary ball mill at 300 r / min. After ball milling, the slurry was dried at 80℃ and then passed through a 60-mesh sieve.

[0191] (4) Granulation

[0192] After secondary ball milling, the obtained powder was granulated by adding a 6 wt.% PVB alcohol solution as a binder. The PVB was measured using a 3 ml plastic pipette, and the powder was added dropwise, with 10 ml of PVB solution required for every 10 g of powder. To ensure uniform mixing of the powder and PVB, an appropriate amount of anhydrous ethanol was added for further grinding. After drying, the powder was passed through a 20-mesh sieve to obtain particles of suitable size.

[0193] (5) Tableting, cold isostatic pressing

[0194] Tableting was performed using a 10mm diameter mold and a tablet press. Each time, 0.35g of free-flowing powder was weighed and poured into the steel mold. Pressure was slowly increased to 10MPa and held for 60s to obtain round tablets with a diameter of 10mm and a thickness of 1.0mm. The round tablets were then placed in sealing bags, sealed using a vacuum sealer, and placed in a cold isostatic press at 200MPa for 5 minutes to further compact the tablets.

[0195] (6) De-glue

[0196] After cold isostatic pressing, the round disc is placed in the glue removal furnace and slowly heated to 600℃ for 60 minutes to remove glue, after which it is cooled down with the furnace.

[0197] (7) Sintering

[0198] After the binder was removed, the sample was placed in a crucible. The pre-fired powder was embedded into the upper and lower surfaces of the sample for powder embedding. The crucible was then covered and placed in a muffle furnace. The temperature was increased to 1150℃ at a rate of 3-5℃ / min and held for 3 hours for sintering. The sample was then cooled to room temperature with the furnace to obtain a lead-free piezoelectric randomly oriented ceramic based on sodium bismuth titanate, named randomly oriented ceramic-Sr. 0.04 Ta 0.006 .

[0199] (8) Polishing, ultrasonic treatment, silver plating, and silver infiltration

[0200] After removal, both sides of the sample need to be polished to remove the ceramic surface layer. The ceramic thickness is ground to 0.6-0.8 mm using 600-grit and 800-grit diamond sandpaper. After polishing, the sample is ultrasonically cleaned, removed, and dried before silver plating. After drying, silver paste is evenly applied to both sides of the sample using screen printing technology. After drying on a heating platform, it is placed in a box furnace for silver infiltration. The silver infiltration program is 720℃ for 15 minutes, followed by natural cooling, resulting in a silver-plated randomly oriented ceramic sample. After polarization with a 3kV / mm voltage at room temperature, a testable randomly oriented Sr ceramic is obtained. 0.04 Ta 0.006 .

[0201] Characterization and performance testing of ceramics in Experiment Example 1

[0202] The three materials prepared in Example 1 and Comparative Example 1 (sheet-like Bi4Ti3O prepared in a pure KCl system) are as follows: 12 Plate-like Bi4Ti3O prepared under template grains and NaCl-KCl system 12 Template grains, testable textured ceramics - Sr 0.04 Ta 0.006 Unmodified textured ceramics - Sr available for testing 0.04 Ta 0.006 Randomly oriented ceramics-Sr available for testing 0.04 Ta 0.006 For the sample, perform the following characterization or performance tests:

[0203] (1) Characterization of phase structure

[0204] Four materials (sheet-like Bi4Ti3O4 prepared in a pure KCl system) were prepared according to Example 1, Comparative Example 1, and Comparative Example 2. 12 Template grains, testable textured ceramics - Sr 0.04 Ta 0.006 Unmodified textured ceramics - Sr available for testing 0.04 Ta 0.006 Randomly oriented ceramics-Sr available for testing 0.04Ta 0.006 Phase structure characterization was performed.

[0205] This experiment used an X-ray diffractometer (D8Advance) to measure the XRD patterns of the samples, such as... Figure 1 As shown, information such as the crystal structure, phase composition, and texture degree of the textured ceramic can be analyzed from the XRD pattern. The scanning angle range is between 10° and 80°, and the test step size is 0.05°. The texture degree of the textured ceramic in the <00l> direction is calculated using the Lotgering factor formula based on the obtained XRD pattern. Figure 1 All diffraction peaks were consistent with the standard PDF card (PDF#72-1019) for BiT. No diffraction peaks of the second phase were found in the sample, indicating that pure phase BiT template grains can be obtained by using KCl as molten salt under the condition of holding at 1140℃ for 8h.

[0206] like Figure 2 and Figure 3 As shown, compared with randomly oriented ceramics, the prepared textured ceramic -Sr 0.04 Ta 0.006 The intensity of the {200} diffraction peak is significantly enhanced, and the textured ceramic grains are along <001> Orientation, obtained through calculation, is found in the improved textured ceramic -Sr 0.04 Ta 0.006 The texture density is 93%. However, the unmodified textured ceramic - Sr 0.04 Ta 0.006 Compared to the improved textured ceramics -Sr 0.04 Ta 0.006 The appearance of new impurity phases indicates that the template grains sintered using the mixed salt NaCl-KCl system may contain Na. 0.5 Bi 8. 5Ti7O 27 Casting can produce textured ceramics with stoichiometric deviations, which affects the performance of the sample.

[0207] (2) Scanning electron microscopy (SEM) characterization

[0208] The materials prepared in Example 1 and Comparative Example 1 (sheet-like Bi4Ti3O prepared in a pure KCl system) 12 Plate-like Bi4Ti3O prepared under template grains and NaCl-KCl system 12 Plate-like Bi4Ti3O prepared under template grains and NaCl-KCl system 12 Template grains, modified textured ceramics - Sr 0.04 Ta 0.006 Phase structure characterization was performed. A desktop scanning electron microscope (TM4000Plus) was used to image the surface and cross-section of the ceramic samples.

[0209] like Figure 4 and Figure 5 As shown, sheet-like Bi₄Ti₃O₃ prepared in a pure KCl system 12 Plate-like Bi4Ti3O prepared under template grains and NaCl-KCl system 12 The template grains were all plate-like and relatively fully crystallized. By measuring the width and thickness of the plate-like grains in the SEM images and calculating their orientation ratio (L / D, the ratio of average length in the horizontal direction to average thickness in the vertical direction), it was found that the template grains synthesized using the KCl molten salt system had a radial length of 9-20 μm and a thickness of approximately 0.3 μm; while the template grains synthesized using the NaCl-KCl molten salt system had a size of 5-11 μm and a thickness of approximately 0.35 μm. The former has a larger orientation ratio than the latter, making it more suitable for tape casting. Figure 6 It can be seen that the improved textured ceramic grains grow well, with clear and distinct boundaries. The crystal grains are stacked layer by layer like bricks, and the grain size grows along the template direction.

[0210] Figure 6 This is a microscopic morphology image of the cross-section of the textured ceramic prepared in Example 1. From Figure 6 It can be seen that the grain growth is good, with clear and distinct boundaries, and the crystal grains are stacked layer by layer like bricks. Because the template grains absorb and react with the surrounding raw materials during sintering, the grain size is relatively large and grows along the template direction. Inside the ceramic, the grains are still arranged in the same direction and are blocky, but some gaps are inevitable between the grains. This is partly because the textured ceramic is made by hot pressing layers, which requires the addition of more additives during the preparation process, making it impossible to achieve the same density as the traditional solid-state method; and partly because the grain size of the textured ceramic is relatively large, so some gaps remain between the grains during the growth process, preventing complete densification. However, the good texture of the ceramic is still evident, indicating that the selected template grains are suitable for this composition of ceramic, and the tape casting and hot pressing processes are effective.

[0211] (3) Electro-strain performance test

[0212] The materials (modified textured ceramic-Sr) prepared in Example 1 and Comparative Example 1 0.04 Ta 0.006 Unmodified ceramics - Sr 0.04 Ta 0.006 Electrostrain performance was tested. This experiment used a ferroelectric strain testing platform (AirACCTTF-2000) to measure the electrostrain performance of the samples under an alternating electric field. The results of Example 1 are as follows: Figure 7 As shown, the results of Comparative Example 1 are as follows: Figure 8 As shown.

[0213] like Figure 7As shown, when the Sr content is 0.04% and the Ta content is 0.006%, the modified textured ceramic-Sr 0.04 Ta 0.006 The maximum unipolar strain reached 1.12%@6kV / mm. For example... Figure 8 As shown, under the same test conditions, the unmodified textured ceramic -Sr 0.04 Ta 0.006 The unipolar strain is 0.37%@6kV / mm. Combined with the phase structure characterization results, it can be seen that this invention introduces Sr into the A-site of the sodium bismuth titanate-potassium bismuth titanate (BNT-BKT) binary solid solution system. 2+ And B position introduces Ta 5+ By performing A- and B-site co-ion doping modification and combining it with an improved casting process, the texture and purity of ceramics can be improved, thereby enhancing their electrostrain performance.

[0214] This invention provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric textured ceramics with excellent electrostrain properties, by introducing Sr at the A-site of the sodium bismuth titanate-potassium bismuth titanate (BNT-BKT) binary solid solution system. 2+ And B position introduces Ta 5 + Bismuth titanate template grains with high purity, large size, and high aspect ratio were prepared by A-site and B-site co-doping in a KCl single molten salt system using the molten salt method. Then, a reactive template grain growth method was employed. By improving the casting slurry ratio, using a double casting blade, and employing a two-stage isostatic pressing process followed by a single hot pressing process, a dense sample with higher purity and better electrostrain performance compared to the unmodified textured ceramic was finally obtained. This method is simple, easy to operate, and low-cost, saving experimental costs and equipment investment, and has good practical prospects in the field of electrostrain materials.

[0215] It should be noted that the sheet-like BiT template grains prepared by using a single KCl molten salt system in a muffle furnace at 1140℃ for 8 hours have advantages such as high purity, large size, and large aspect ratio. They can be "laid out" in the cast film under the action of the casting doctor blade, making them more suitable for casting than template grains prepared by a NaCl-KCl mixed molten salt system.

[0216] Furthermore, the present invention employs a dual-layer casting scraper device to perform secondary casting of the slurry, resulting in a smoother single-layer cast film with more orderly grain arrangement, thereby improving the texture of the textured ceramic.

[0217] Furthermore, the innovative formulation of the casting paste in this invention involves adding only three types of adhesives as additives, each in an amount of Bi4Ti3O4. 12The solvent added consists of 4wt% castor oil (2% by total mass of TiO2, Na2CO3, K2CO3, Ta2O5, SrCO3, and Bi2O3), 48wt% polyvinyl butyral (PVB) (9% by total mass), and 40wt% dibutyl phthalate (DBP) (10% by total mass). The total mass of the solvent added in both cases is Bi4Ti3O. 12 The total mass of TiO2, Na2CO3, K2CO3, Ta2O5, SrCO3 and Bi2O3 is 60%, which saves process costs while obtaining a slurry with the best fluidity and ductility for casting.

[0218] Furthermore, by doping the sodium bismuth titanate-potassium bismuth titanate (BNT-BKT) binary solid solution ceramic with Sr doping to replace the A site and Ta doping to replace the B site, the co-doping of Sr2+ and Ta4+ leads to the formation of cation vacancies inside the crystal lattice, which disrupts the long-range order of the ferroelectrics in the piezoelectric ceramic, making the domains more prone to orientation. As the applied electric field increases, the relaxor phase gradually transforms into the ferroelectric phase, thereby improving the piezoelectric performance.

[0219] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing sodium bismuth titanate-based lead-free piezoelectric textured ceramics, characterized in that, Includes the following steps: Bismuth titanate template crystals were prepared using a single potassium chloride molten salt system, based on the chemical composition [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ] 0.96 Sr 0.04 Ti 1-x Ta x O3, 0< x <0.01, weigh the bismuth titanate template crystal, titanium dioxide, sodium carbonate, potassium carbonate, strontium carbonate and tantalum pentoxide, mix with bismuth oxide, additives and solvent to obtain a ceramic slurry, use the reactive template grain growth method, and use a casting process to cast the ceramic slurry with a double scraper to obtain a single-layer cast film, stack the single-layer cast films to obtain a cast film sheet, and sequentially pass the cast film sheet through hot pressing, first cold isostatic pressing, glue removal, second cold isostatic pressing and sintering to obtain the sodium bismuth titanate-based lead-free piezoelectric textured ceramic.

2. The method according to claim 1, characterized in that, The texture of the sodium bismuth titanate-based lead-free piezoelectric textured ceramic is >90%.

3. The method according to claim 1, characterized in that, The textured ceramic grains of the sodium bismuth titanate-based lead-free piezoelectric textured ceramic are along... <001> orientation.

4. The method according to claim 1, characterized in that, The preparation method of the bismuth titanate template crystal includes the following steps: Bi2O3 and TiO2 are mixed, a single molten salt is added, and after ball milling, drying and calcination, the bismuth titanate template crystal is obtained.

5. The method according to claim 1, characterized in that, The additives include polyvinyl butyral, dibutyl phthalate, polyethylene glycol, and castor oil.

6. The method according to claim 1, characterized in that, The stacking method includes: bonding and pressing two single-layer cast films at 70~80°C to make them fit tightly together, and repeating the operation to stack multiple cast films to a thickness of 2~3mm.

7. The method according to claim 1, characterized in that, The hot pressing includes hot pressing at 60-80℃ and 50-60MPa for 15-20 minutes.

8. The method according to claim 1, characterized in that, The glue removal process includes: heating to 240°C for 120 minutes at room temperature, heating to 350°C for 270 minutes, heating to 600°C for 500 minutes, holding at that temperature for 80 minutes, and then cooling with the furnace.

9. The method according to claim 1, characterized in that, The first cold isostatic pressing includes: holding the pressure at 200~250MPa for 5~10min; and / or, the second cold isostatic pressing includes: holding the pressure at 200~250MPa for 5~10min.

10. The method according to claim 1, characterized in that, The sintering process includes heating to 1150°C at a rate of 3-5°C / min and holding at that temperature for 8 hours.

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