High electro-strained sodium bismuth titanate-based lead-free piezoelectric ceramic material and method for manufacturing the same

Abstract

This invention relates to the field of piezoelectric ceramics technology, specifically to a high-electrostrain bismuth sodium titanate-based lead-free piezoelectric ceramic material and its preparation method. The general chemical formula of the ceramic material is: (Bi 0.5 Na 0.5 ) (1‑x) (Ca 0.5 Sr 0.5 ) x Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02 O3, in which x =0.03~0.4. Its preparation method includes: weighing raw materials according to stoichiometric ratio, ball milling and mixing, pre-calcination synthesis, secondary ball milling, granulation and molding, and debinding sintering. This invention introduces Ca at the A-site. 2+ and Sr 2+ Constructing quasi-isomorphic phase boundaries to lower the polarization energy barrier; introducing Sn through the B site. 4+ and Sb 3+ The formation of defect dipoles pins domain walls and enhances the random field. These two factors work synergistically to significantly improve the electrostrain properties of the material; the prepared ceramic exhibits a maximum strain of [value missing] under an electric field of 100 kV / cm. S max The inverse piezoelectric coefficient is 2.18%, the inverse piezoelectric coefficient is 2572 pm / V, and the memory strain is 2.18%. S r With a lead content of 1.19%, and a simple, environmentally friendly process, it is suitable for mass production and has broad application prospects in the field of high-performance lead-free actuators.

Description

Technical Field

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

[0002] Perovskite piezoelectric ceramics (ABO3) are important functional materials for converting mechanical energy into electrical energy. Currently, lead-containing piezoelectric ceramics, especially PbTi... 1-x Zr x Lead (PZT) oxide (O3) is widely used in sensors and actuators due to its excellent piezoelectric properties. However, the lead in these ceramics poses environmental and health risks during synthesis and use. Therefore, there is an urgent need to develop high-performance lead-free piezoelectric ceramics to replace PZT. In recent years, various lead-free piezoelectric ceramic systems have been developed, such as BaTiO3 (BT), K... 0.5 Na 0.5 NbO3 (KNN), BiFeO3 (BFO) and Bi 0.5 Na 0.5 TiO3 (BNT). Among them, BNT-based piezoelectric ceramics have attracted much attention due to their huge electrostrain and high Curie temperature, and have become one of the most promising lead-free piezoelectric materials in the field of actuator applications.

[0003] To optimize the piezoelectric properties of BNT-based ceramics, chemical doping is the mainstream method. Incorporating isovalent elements or multi-components into BNT ceramics can establish a quasi-isomorphic phase boundary (MPB) between the rhombohedral (R) and tetragonal (T) phases. The MPB lowers the polarization switching energy barrier, allowing the ceramic to undergo a reversible ferroelectric (FE)-relaxed ferroelectric (RE) phase transition under an electric field, resulting in large electroinduced strain. Recent studies have shown that the strain of many BNT-based ceramics has exceeded 0.5%. For example, Li et al. (Advanced Functional Materials, 2022, 32(32): 2202307) designed a strain of 0.97Bi near the MPB. 0.47 Na 0.47 Ba 0.06 TiO3-0.03K 0.47 Na 0.47 Li 0.06 Nb 0.99 Sb 0.01 O 2.99A strain response of 0.51% was achieved by embedding a nano-ferroelectric phase within a relaxor ferroelectric matrix and utilizing the low energy barrier near the MPB to promote a field-induced FE-RE phase transition. However, the high energy barrier of the field-induced FE phase transition requires a higher driving electric field, resulting in the MPB effect on BNTs often failing to achieve an electrical strain exceeding 0.7%. This severely limits the application of BNT-based ceramics in high-performance piezoelectric actuators. Furthermore, the electrostrain of existing sodium bismuth titanate-based piezoelectric ceramics is generally low, mostly not exceeding 1%, while components with high electrostrain contain lead, which can easily cause environmental pollution. These issues limit the practical application of sodium bismuth titanate-based lead-free piezoelectric ceramics.

[0004] Therefore, designing a lead-free piezoelectric ceramic with stable large electrostrain is an important technical problem that urgently needs to be solved. Summary of the Invention

[0005] In view of this, the present invention prepares a high-electrostrained sodium bismuth titanate-based lead-free piezoelectric ceramic material by constructing quasi-isomorphic phase boundaries and introducing B-site defects. Its general chemical formula is (Bi... 0.5 Na 0.5 ) (1-x) (Ca 0.5 Sr 0.5 ) x Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02 O3, in which x = 0.03~0.4. Under the synergistic effect of a local random field induced by the coexistence of multiple cations, combined with the quasi-isomorphic phase boundary and defect dipole pinning effect, the reversible domain flipping of this ceramic is significantly enhanced. The optimal performance is achieved by the maximum strain at an electric field of 100 kV / cm. S max It is 2.18%, memory strain S r The inverse piezoelectric coefficient is 1.19%. The efficiency is 2572 pm / V. The preparation method of this invention is simple, produces stable product performance, and is suitable for mass production. This invention has significant social and environmental benefits, greatly reducing lead pollution and representing an important development direction for high-performance green piezoelectric materials.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a high-electrostrain bismuth sodium titanate-based lead-free piezoelectric ceramic material, the general chemical formula of which is: (Bi 0.5 Na 0.5 ) (1-x) (Ca 0.5 Sr 0.5 ) xTi 0.98 (Sn 0.5 Sb 0.4 ) 0.02 O3, of which x The value range is 0.03 to 0.4.

[0007] Preferably, the x The preferred value range is 0.06 to 0.15.

[0008] In a second aspect, the present invention provides a method for preparing a high electrostrain sodium bismuth titanate-based lead-free piezoelectric ceramic material as described in the first aspect, comprising the following steps: S1. Weigh out Na source, Bi source, Ca source, Sr source, Ti source, Sn source and Sb source according to the stoichiometric ratio of the general formula of the chemical composition, mix them, ball mill and dry them to obtain mixed powder; S2. The mixed powder obtained in step S1 is pre-calcined to obtain pre-calcined powder; S3. The pre-fired powder obtained in step S2 is ball-milled, dried, and sieved to obtain ceramic powder. S4. The ceramic powder obtained in step S3 is granulated and shaped to obtain a green body. Then, the green body is debinded and sintered to obtain the high electrostriction sodium bismuth titanate-based lead-free piezoelectric ceramic material.

[0009] Preferably, the Na source includes Na2CO3, the Bi source includes Bi2O3, the Ca source includes CaCO3, the Sr source includes SrCO3, the Ti source includes TiO2, the Sn source includes SnO2, and the Sb source includes Sb2O3.

[0010] Preferably, in steps S1 and S3, the ball milling is a wet ball milling, the ball milling medium includes anhydrous ethanol, the grinding balls include zirconia balls, and the ball milling speed is 200~400 rpm.

[0011] Preferably, in step S2, the preheating temperature is 850℃~900℃, and the holding time is 2~4 h.

[0012] Specifically, the perovskite phase formation temperature of BNT-based ceramics is usually above 800℃. 850-900℃ can ensure that the doped ions diffuse fully and dissolve into the BNT lattice to form the main crystalline phase, while avoiding excessive temperature that would cause severe Bi / Na volatilization or hard agglomeration of powder. Holding at this temperature for 2-4 hours ensures that the reaction is complete.

[0013] Preferably, in step S4, the molding pressure is 50~300 MPa and the holding time is 3~5 min.

[0014] Specifically, a pressure range of 50-300 MPa ensures that the green body has sufficient density and strength. If the pressure is too low, the green body will be loose, and if it is too high, stress or delamination may occur.

[0015] Preferably, in step S4, the glue discharge temperature is 500℃~600℃, and the heat preservation time is 1~2 h.

[0016] Specifically, if the temperature is too low, decomposition will be incomplete; if it is too high or too rapid, the organic matter will decompose violently, producing gas, causing the green body to crack and bubble. Slowly raising the temperature and holding it at that temperature for a sufficient period of time ensures that the organic matter is completely oxidized into CO2 and discharged, rather than leaving residual carbon. Residual carbon may be reduced to high-valence ions (such as Sn) in the reducing atmosphere of subsequent high-temperature sintering. 4+ Ti 4+ (etc.), which leads to electronic conductivity, severely damaging insulation and piezoelectric properties.

[0017] Preferably, in step S4, the sintering temperature is 1125℃~1225℃, and the holding time is 2~4 h.

[0018] Specifically, the densification sintering temperature of BNT-based ceramics is usually within this range. If the temperature is too low, the density will be poor and the performance will deteriorate; if the temperature is too high, it will lead to serious loss of volatile elements such as Bi, Na, and Sb, deviation of stoichiometry, and formation of a large number of defects. A holding time of 2-4 hours is sufficient to allow the grains to grow fully and achieve high density, while avoiding prolonged high temperature which will aggravate volatilization.

[0019] Thirdly, the present invention provides an application of the high electrostricted bismuth titanate sodium-based lead-free piezoelectric ceramic material as described in the first aspect in the field of piezoelectric ceramics.

[0020] Compared with the prior art, the advantages of the present invention are as follows: (1) The sodium bismuth titanate-based lead-free piezoelectric ceramic prepared in this invention is produced by doping Ca at site A. 2+ and Sr 2+ Ions modulate the NR-ER phase boundary to near room temperature. 2+ and Sr 2+ The large ionic radius of the ions enhances the lattice distortion of BNT-based ceramics and synergistically regulates the relaxation properties of the BNT matrix. Meanwhile, the low energy barrier near MPB promotes field-induced phase transition and generates significant electro-induced strain.

[0021] (2) The sodium bismuth titanate-based lead-free piezoelectric ceramic prepared in this invention is non-stoichiometrically doped with Sn at the B site. 4+ and Sb 3+ Ions, through charge compensation, introduce oxygen vacancies to form defect dipoles. Sn 4+ and Sb 3+Ions enhance the stability of the relaxed state in the BNT matrix. Defect dipoles align with ferroelectric domains under the action of an external field, forming a strong random field and changing the energy barrier of polarization rotation under different electric field directions.

[0022] (3) The sodium bismuth titanate-based lead-free piezoelectric ceramic prepared in this invention introduces local chemical disorder through multi-cation doping at the A-site and B-site, forming a random field and simultaneously suppressing polar phase transitions caused by temperature changes. Under the synergistic effect of multiple mechanisms, a maximum electrostriction of 2.18% was obtained at an electric field of 100 kV / cm and 0.1 Hz, with a memory strain of 1.19% and an inverse piezoelectric coefficient. Up to 2572 pm / V.

[0023] (4) The preparation method of the present invention is simple in steps, produces stable product performance, and is suitable for mass production. The present invention has significant social and environmental benefits, can greatly reduce lead pollution, and represents an important development direction for high-performance green piezoelectric materials. Attached Figure Description

[0024] Figure 1 The image shows a scanning electron microscope (SEM) image of the sodium bismuth titanate-based ceramic obtained in Example 1 of this invention. Figure 2 The bipolar strain-electric field curve of the sodium bismuth titanate-based ceramic obtained in Example 1 of this invention; Figure 3 The image shows the unipolar strain-electric field curve of the sodium bismuth titanate-based ceramic after aging, obtained in Example 1 of this invention. Figure 4 This is a scanning electron microscope image of the sodium bismuth titanate-based ceramic obtained in Example 2 of the present invention; Figure 5 The bipolar strain-electric field curve of the sodium bismuth titanate-based ceramic obtained in Example 2 of this invention; Figure 6 The bipolar strain-electric field curve of the sodium bismuth titanate-based ceramic obtained in Comparative Example 1 of this invention; Figure 7 The bipolar strain-electric field curve of the sodium bismuth titanate-based ceramic obtained in Comparative Example 2 of this invention is shown. Figure 8 The bipolar strain-electric field curve of the sodium bismuth titanate-based ceramic obtained in Example 3 of this invention; Figure 9 The image shows the bipolar strain-electric field curve of the sodium bismuth titanate-based ceramic obtained in Example 4 of this invention.

[0025] Figure 10 The image shows the bipolar strain-electric field curve of the sodium bismuth titanate-based ceramic obtained in Example 5 of this invention. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0028] In this document, the terms “containing,” “comprising,” or “including” are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0029] In this document, the terms “optional,” “optionally,” or “optional” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0031] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field. Specifically, Na₂CO₃ (99.8% purity), Bi₂O₃ (99% purity), CaCO₃ (99.5% purity), SrCO₃ (99% purity), TiO₂ (99.99% purity), SnO₂ (99.99% purity), and Sb₂O₃ (99.99% purity) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; the high-purity silver target (99.99% purity) used in magnetron sputtering was purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd.

[0032] Example 1

[0033] This embodiment provides a high-electrostrain sodium bismuth titanate-based lead-free piezoelectric ceramic material and its preparation method, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.88 (Ca 0.5 Sr 0.5 )0.12 Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02 The stoichiometric proportions of O3 were as follows: Na2CO3 (99.8% purity), Bi2O3 (99% purity), CaCO3 (99.5% purity), SrCO3 (99% purity), TiO2 (99.99% purity), SnO2 (99.99% purity), and Sb2O3 (99.99% purity), weighed out in the following proportions: 18.6934 g Na2CO3, 82.8373 g Bi2O3, 4.8285 g CaCO3, 7.1578 g SrCO3, 62.6243 g TiO2, 1.2058 g SnO2, and 0.9330 g Sb2O3. The mixture was added to a ball mill jar and ball milled using a wet ball milling method with anhydrous ethanol as the milling medium. Zirconia balls were used as the grinding media, and a nylon jar was used. The ball mill speed was 400 rpm. After ball milling for 6 hours, the mixture was dried. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% polyvinyl alcohol binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 200 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0034] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1175℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0035] Furthermore, the microstructure of the sodium bismuth titanate-based lead-free piezoelectric ceramic prepared in Example 1 was characterized using field emission scanning electron microscopy, and the grain size was statistically analyzed. The test results are as follows: Figure 1 As shown in the figure, the ceramic is dense overall, with an average grain size of approximately 2.11 μm.

[0036] Furthermore, the sodium bismuth titanate-based ceramic prepared in Example 1 was polished to a thickness of 0.25 mm. Conductive electrodes were then deposited onto the polished sodium bismuth titanate-based ceramic surface using vapor deposition or magnetron sputtering. The target material used for magnetron sputtering was a high-purity silver target, the working atmosphere was argon, the working pressure was fixed at 3 Pa, the argon flow rate was controlled at 90 sccm, the sputtering temperature was 25 °C, the sputtering power was 100 W, the sputtering time was 5 min, and the substrate stage rotation speed was 15 rpm.

[0037] An AC electric field with a frequency of 0.1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply. The electrostrain of the ceramics was measured using a laser interferometer. Figure 2 As shown in the figure, the maximum electrostriction of the ceramic under an electric field of 100 kV / cm can be observed. S max Up to 1.20%, reverse piezoelectric coefficient It can reach 1325 pm / V.

[0038] A DC electric field of 70 kV / cm was applied to the electrode-coated sodium bismuth titanate-based ceramic using a high-voltage DC power supply. After holding the voltage for 2 hours, the ceramic was removed and aged for 2 weeks. A unipolar AC electric field with a frequency of 0.1 Hz was then applied to the aged sodium bismuth titanate-based ceramic using a high-voltage AC power supply. The electrostriction of the ceramic was measured using a laser interferometer. The unipolar strain-electric field curve is shown below. Figure 3 As shown. From Figure 3 As can be seen, the electrostriction of the polarized and aged sample is significantly increased, with the maximum unipolar electrostriction at an electric field of 100 kV / cm reaching a certain value. S max Up to 2.18%, reverse piezoelectric coefficient It reached 2572 pm / V.

[0039] Example 2

[0040] This embodiment provides a high-electrostrain sodium bismuth titanate-based lead-free piezoelectric ceramic material and its preparation method, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.85 (Ca 0.5 Sr 0.5 ) 0.15 Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02The stoichiometric proportions of O3 were as follows: Na2CO3 (99.8% purity), Bi2O3 (99% purity), CaCO3 (99.5% purity), SrCO3 (99% purity), TiO2 (99.99% purity), SnO2 (99.99% purity), and Sb2O3 (99.99% purity), weighed out in the following proportions: 18.0561 g Na2CO3, 80.0133 g Bi2O3, 6.0356 g CaCO3, 8.9473 g SrCO3, 62.6243 g TiO2, 1.2058 g SnO2, and 0.9330 g Sb2O3. The mixture was added to a ball mill jar and ball milled using a wet ball milling method. The ball milling medium was anhydrous ethanol, and the grinding balls were zirconia balls. The ball mill jar was made of nylon, and the mill speed was 200 rpm. After ball milling for 6 hours, the mixture was dried. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 850°C and a holding time of 4 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 300 MPa, the holding time is 3 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0041] (5) The green blank obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 500℃, the heating rate is 3℃ / min, the holding time is 1 h, the sintering temperature is 1125℃, the heating rate is 5℃ / min, and the holding time is 4 h.

[0042] Furthermore, the microstructure of the sodium bismuth titanate-based lead-free piezoelectric ceramic prepared in Example 2 was characterized using field emission scanning electron microscopy. The test results are as follows: Figure 4 As shown in the figure, the ceramic is dense overall, with an average grain size of about 2.20 μm.

[0043] Furthermore, the sodium bismuth titanate-based ceramic prepared in Example 2 was polished to a thickness of 0.25 mm, and conductive electrodes were deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0044] An AC electric field with a frequency of 0.1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply. The electrostrain of the ceramics was measured using a laser interferometer. Figure 5 As shown in the figure, the maximum electrostriction of the ceramic under an electric field of 100 kV / cm can be observed.S max Reaching 0.69%, reverse piezoelectric coefficient Up to 748 pm / V.

[0045] Comparative Example 1

[0046] This comparative example provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric ceramics, including the following steps: (1) According to the general chemical formula Bi 0.5 Na 0.5 The stoichiometric ratio of TiO3 was as follows: Na2CO3 (purity 99.8%), Bi2O3 (purity 99%), and TiO2 (purity 99.99%) were weighed and mixed in the following proportions: 21.2425 g Na2CO3, 94.1333 g Bi2O3, and 63.9024 g TiO2. The mixture was added to a ball mill jar and ball milled using a wet ball milling method. The ball milling medium was anhydrous ethanol, the grinding balls were zirconia balls, and the ball mill jar was a nylon jar. The ball mill speed was 200 rpm, and the mixture was dried after 6 hours of ball milling. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 200 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0047] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0048] Compared with Example 1, Comparative Example 1 is undoped pure sodium bismuth titanate ceramic.

[0049] Furthermore, the sodium bismuth titanate-based ceramic prepared in Comparative Example 1 was polished to a thickness of 0.25 mm, and conductive electrodes were deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0050] An AC electric field with a frequency of 0.1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply. The electrostrain of the ceramics was measured using a laser interferometer. Figure 6As shown in the figure, the maximum electrostriction of the ceramic under an electric field of 100 kV / cm can be observed. S max The inverse piezoelectric coefficient is 0.41%. The value is 441 pm / V, which is far inferior to the performance of Examples 1 and 2.

[0051] Comparative Example 2

[0052] This comparative example provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric ceramics, including the following steps: (1) According to the general chemical formula Bi 0.5 Na 0.5 Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02 The stoichiometric ratio of O3 was as follows: Na2CO3 (purity 99.8%), Bi2O3 (purity 99%), and TiO2 (purity 99.99%) were weighed and mixed in the following proportions: 21.2425 g Na2CO3, 94.1333 g Bi2O3, 62.6243 g TiO2, 1.2058 g SnO2, and 0.9330 g Sb2O3. The mixture was added to a ball mill jar and ball milled using a wet ball milling method. The ball milling medium was anhydrous ethanol, the grinding balls were zirconia balls, and the ball mill jar was a nylon jar. The ball mill speed was 200 rpm, and the mixture was dried after 6 hours of ball milling. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 200 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0053] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0054] Compared with Example 1, the sodium bismuth titanate-based ceramic of Comparative Example 2 was undoped at site A, while the doping elements and proportions at site B were the same as in Example 1.

[0055] Furthermore, the sodium bismuth titanate-based ceramic prepared in Comparative Example 2 was polished to a thickness of 0.25 mm, and conductive electrodes were deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0056] An AC electric field with a frequency of 1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply. The electrostriction of the ceramics was measured using a laser interferometer. Figure 7 As shown in the figure, the maximum electrostriction of the ceramic under an electric field of 80 kV / cm can be observed. S max It is 0.35%, the inverse piezoelectric coefficient. The efficiency was 443 pm / V, which is still lower than that of Examples 1 and 2. Comparative Example 2 has a small amount of Sn and Sb doping at the B site, but the main body is still a normal ferroelectric based on BNT. It has a macrodomain structure at the microscopic level and a high coercive field. Domain flipping under an electric field requires overcoming a large energy barrier. Therefore, its electroinduced strain mainly comes from domain flipping and elongation, and the strain value is limited.

[0057] Comparative Example 3

[0058] This comparative example provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric ceramics, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.85 (Ca 0.5 Sr 0.5 ) 0.15 The stoichiometric ratio of TiO3 is as follows: Na2CO3 (purity 99.8%), Bi2O3 (purity 99%), CaCO3 (purity 99.5%), SrCO3 (purity 99%), and TiO2 (purity 99.99%) are weighed and mixed in the following proportions: 18.0561 g Na2CO3, 80.0133 g Bi2O3, 6.0356 g CaCO3, 8.9473 g SrCO3, and 63.9024 g TiO2. The mixture is added to a ball mill jar and ball milled using a wet ball milling method. The ball milling medium is anhydrous ethanol, the grinding balls are zirconia balls, and the ball mill jar is a nylon jar. The ball mill speed is 200 rpm. After ball milling for 6 hours, the mixture is dried. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 200 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0059] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0060] Compared with Example 2, the sodium bismuth titanate-based ceramic of Comparative Example 3 was undoped at the B site, while the doping elements and proportions at the A site were the same as in the Example.

[0061] Furthermore, the sodium bismuth titanate-based ceramic prepared in Comparative Example 3 was polished to a thickness of 0.25 mm, and conductive electrodes were deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0062] An AC electric field with a frequency of 0.1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply, and the electrostriction of the ceramics was measured using a laser interferometer. The maximum electrostriction of the ceramics under an electric field of 80 kV / cm was determined. S max The inverse piezoelectric coefficient is 0.39%. The performance of Comparative Example 3 was 504 pm / V, still inferior to that of Examples 1 and 2. The higher Ca and Sr doping levels in Comparative Example 3 introduced stronger chemical disorder and lattice distortion at the A-site, resulting in excessively strong relaxation properties. Its ground state at room temperature was already overly biased towards a nonpolar or weakly polar relaxation state. In contrast, Comparative Example 3 lacked Sn and Sb doping at the B-site, thus missing the slight local lattice distortion caused by differences in Sn electronegativity, and the optimization and additional contribution of Sb acceptor doping and soft pinning effects to the polarization reversal process. Therefore, Comparative Example 3's performance was inferior to that of Examples 1 and 2.

[0063] Comparative Example 4

[0064] This comparative example provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric ceramics, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.9 Sr 0.1 Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02The stoichiometric proportions of O3 were as follows: Na2CO3 (99.8% purity), Bi2O3 (99% purity), CaCO3 (99.5% purity), SrCO3 (99% purity), TiO2 (99.99% purity), SnO2 (99.99% purity), and Sb2O3 (99.99% purity), weighed out in the following proportions: 19.1182 g Na2CO3, 84.7200 g Bi2O3, 11.9297 g SrCO3, 62.6243 g TiO2, 1.2058 g SnO2, and 0.9330 g Sb2O3. The mixture was added to a ball mill jar and ball milled using a wet ball milling method. The ball milling medium was anhydrous ethanol, and the grinding balls were zirconia balls. The ball mill jar was made of nylon, and the milling speed was 200 rpm. After ball milling for 6 hours, the mixture was dried. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 200 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0065] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0066] Compared with Example 1, the sodium bismuth titanate-based ceramic of Comparative Example 4 is doped with Sr at site A only, with a ratio of 0.1, while the doping element and ratio at site B are the same as in Example 1.

[0067] Furthermore, the sodium bismuth titanate-based ceramic prepared in Comparative Example 4 was polished to a thickness of 0.25 mm, and conductive electrodes were deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0068] An AC electric field with a frequency of 0.1 Hz was applied to bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply, and the electrostriction of the ceramics was measured using a laser interferometer. The maximum electrostriction of the ceramics under an electric field of 100 kV / cm was determined. S max The inverse piezoelectric coefficient is 0.49%. The performance was 512 pm / V, higher than Comparative Example 1, but lower than Examples 1 and 2. In Comparative Example 4, only Sr was doped at the A site, mainly introducing unidirectional and uniform lattice expansion. Its mode was relatively simple, and the resulting local stress field and potential field variations were not rich enough. Therefore, the performance of Comparative Example 4 was inferior to Examples 1 and 2.

[0069] Comparative Example 5

[0070] This comparative example provides a method for preparing sodium bismuth titanate-based lead-free piezoelectric ceramics, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.91 (Ca 0.5 Sr 0.5 ) 0.09 Ti 0.98 Sn 0.02 The stoichiometric ratio of O3 was as follows: Na2CO3 (purity 99.8%), Bi2O3 (purity 99%), CaCO3 (purity 99.5%), SrCO3 (purity 99%), TiO2 (purity 99.99%), and SnO2 (purity 99.99%) were weighed and mixed in the following proportions: 19.3307 g Na2CO3, 85.6613 g Bi2O3, 3.6213 g CaCO3, 5.3684 g SrCO3, 62.6243 g TiO2, and 2.4116 g SnO2. The mixture was added to a ball mill jar and ball milled using a wet ball milling method with anhydrous ethanol as the milling medium. Zirconia balls were used as the grinding balls, and a nylon jar was used. The ball mill speed was 200 rpm. The mixture was ball milled for 6 hours and then dried. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 200 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0071] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0072] Compared with Example 1, the doping elements and proportions at the A-site of the sodium bismuth titanate-based ceramic in Comparative Example 5 are the same as those in Example 1, while only Sn is doped at the B-site at a proportion of 0.02.

[0073] Furthermore, the sodium bismuth titanate-based ceramic prepared in Comparative Example 5 was polished to a thickness of 0.25 mm, and conductive electrodes were deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0074] An AC electric field with a frequency of 0.1 Hz was applied to bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply, and the electrostriction of the ceramics was measured using a laser interferometer. The maximum electrostriction of the ceramics under an electric field of 100 kV / cm was determined. S max It is 0.47%, the inverse piezoelectric coefficient. The efficiency was 494 pm / V, which is higher than that of Comparative Example 1, but lower than that of Examples 1 and 2. In Comparative Example 5, the B site was not doped with Sb. The lack of Sb element resulted in the optimization and additional contribution of the defective dipole to the polarization reversal process by the main doping and soft pinning effect. Therefore, the performance of Comparative Example 5 was lower than that of Examples 1 and 2.

[0075] Example 3

[0076] This embodiment provides a high-electrostrain sodium bismuth titanate-based lead-free piezoelectric ceramic material and its preparation method, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.97 (Ca 0.5 Sr 0.5 ) 0.03 Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02 The stoichiometric proportions of O3 were as follows: Na2CO3 (99.8% purity), Bi2O3 (99% purity), CaCO3 (99.5% purity), SrCO3 (99% purity), TiO2 (99.99% purity), SnO2 (99.99% purity), and Sb2O3 (99.99% purity). The proportions were: 20.6052 g Na2CO3, 91.3093 g Bi2O3, 0.3018 g CaCO3, 0.4474 g SrCO3, 62.6243 g TiO2, 1.2058 g SnO2, and 0.9330 g Sb2O3. The mixture was added to a ball mill jar and ball milled using a wet ball milling method. The ball milling medium was anhydrous ethanol, and the grinding balls were zirconia balls. The ball mill jar was made of nylon and the mill speed was 200 rpm. The mixture was ball milled for 6 hours and then dried. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 50 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0077] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1225℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0078] Compared with Example 1, the A-site doping element of the sodium bismuth titanate-based ceramic in Example 3 is the same as that in Example 1, with a ratio value of x of 0.03, and the B-site doping element and ratio are the same as those in Example 1.

[0079] Furthermore, the sodium bismuth titanate-based ceramic prepared in Example 3 was polished to a thickness of 0.25 mm, and a conductive electrode was deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0080] An AC electric field with a frequency of 0.1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply. The electrostrain of the ceramics was measured using a laser interferometer. Figure 8 As shown in the figure, the maximum electrostriction of the ceramic under an electric field of 100 kV / cm can be observed. S max The inverse piezoelectric coefficient is 0.50%. The value was 532 pm / V, which is higher than that of Comparative Example 1, but lower than that of Example 1 and Example 2.

[0081] Example 4

[0082] This embodiment provides a high-electrostrain sodium bismuth titanate-based lead-free piezoelectric ceramic material and its preparation method, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.6 (Ca 0.5 Sr 0.5 ) 0.4 Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02The stoichiometric proportions of O3 are as follows: Na2CO3 (99.8% purity), Bi2O3 (99% purity), CaCO3 (99.5% purity), SrCO3 (99% purity), TiO2 (99.99% purity), SnO2 (99.99% purity), and Sb2O3 (99.99% purity). The proportions are: 12.7455 g Na2CO3, 56.4800 g Bi2O3, 16.0949 g CaCO3, 23.8594 g SrCO3, 62.6243 g TiO2, 1.2058 g SnO2, and 0.9330 g Sb2O3. These are added to a ball mill jar. Wet ball milling is used with anhydrous ethanol as the milling medium. Zirconia balls are used, and a nylon jar is used. The ball mill speed is 200 rpm. The milling process is repeated for 6 minutes. Dry after h; (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 200 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0083] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1200℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0084] Compared with Example 1, the A-site doping element of the sodium bismuth titanate-based ceramic in Example 4 is the same as that in Example 1, and the ratio is the same. x The value is 0.4, and the doping element and ratio at the B site are the same as in Example 1.

[0085] Furthermore, the sodium bismuth titanate-based ceramic prepared in Example 4 was polished to a thickness of 0.25 mm, and a conductive electrode was deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0086] An AC electric field with a frequency of 0.1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply. The electrostrain of the ceramics was measured using a laser interferometer. Figure 9 As shown in the figure, the maximum electrostriction of the ceramic under an electric field of 100 kV / cm can be observed. S maxIt is 0.55%, the inverse piezoelectric coefficient. The value was 592 pm / V, which is higher than that of Comparative Example 1, but lower than that of Example 1 and Example 2.

[0087] Example 5

[0088] This embodiment provides a high-electrostrain sodium bismuth titanate-based lead-free piezoelectric ceramic material and its preparation method, including the following steps: (1) According to the general chemical formula (Bi) 0.5 Na 0.5 ) 0.94 (Ca 0.5 Sr 0.5 ) 0.06 Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02 The stoichiometric proportions of O3 were as follows: Na2CO3 (99.8% purity), Bi2O3 (99% purity), CaCO3 (99.5% purity), SrCO3 (99% purity), TiO2 (99.99% purity), SnO2 (99.99% purity), and Sb2O3 (99.99% purity), weighed out in the following proportions: 19.9679 g Na2CO3, 88.4853 g Bi2O3, 2.4142 g CaCO3, 3.5789 g SrCO3, 62.6243 g TiO2, 1.2058 g SnO2, and 0.9330 g Sb2O3. The mixture was added to a ball mill jar and ball milled using a wet ball milling method. The ball milling medium was anhydrous ethanol, and the grinding balls were zirconia balls. The ball mill jar was made of nylon, and the mill speed was 200 rpm. After ball milling for 6 hours, the mixture was dried. (2) The mixture obtained in (1) is placed in a muffle furnace for pre-firing at a temperature of 900°C and a holding time of 2 h. (3) Add the powder obtained from the pre-calcination in (2) to a ball mill jar, and mill the powder with the same parameters as in step (1). After milling for 12 hours, dry the powder. (4) Add 0.3 ml of 8 wt% PVA binder to each gram of powder obtained in (3) to granulate it, and then put it into a mold to press and shape it to obtain a ceramic green body. The diameter of the mold is 16 mm, the molding pressure is 50 MPa, the holding time is 5 min, the green body diameter is 16 mm, and the thickness is 1 mm.

[0089] (5) The green body obtained in (4) is placed in a muffle furnace for debinding and sintering. The debinding temperature is 600℃, the heating rate is 3℃ / min, the holding time is 2 h, the sintering temperature is 1225℃, the heating rate is 5℃ / min, and the holding time is 2 h.

[0090] Compared with Example 1, the A-site doping element of the sodium bismuth titanate-based ceramic in Example 5 is the same as that in Example 1, and the ratio is the same. x The value is 0.06, and the doping element and ratio at the B site are the same as in Example 1.

[0091] Furthermore, the sodium bismuth titanate-based ceramic prepared in Example 5 was polished to a thickness of 0.25 mm, and a conductive electrode was deposited on the surface of the polished sodium bismuth titanate-based ceramic by vapor deposition or magnetron sputtering.

[0092] An AC electric field with a frequency of 0.1 Hz was applied to sodium bismuth titanate-based ceramics coated with electrodes using a high-voltage AC power supply. The electrostrain of the ceramics was measured using a laser interferometer. Figure 10 As shown in the figure, the maximum electrostriction of the ceramic under an electric field of 100 kV / cm can be observed. S max It is 0.62%, the inverse piezoelectric coefficient. The value was 640 pm / V, which is higher than that of Comparative Example 1, but lower than that of Example 1 and Example 2.

[0093] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A high-electrostrain bismuth sodium titanate-based lead-free piezoelectric ceramic material, characterized in that, Its general chemical formula is: (Bi) 0.5 Na 0.5 ) (1-x) (Ca 0.5 Sr 0.5 ) x Ti 0.98 (Sn 0.5 Sb 0.4 ) 0.02 O3, of which x The value range is 0.03 to 0.

4.

2. The high-electrostrain sodium bismuth titanate-based lead-free piezoelectric ceramic material according to claim 1, characterized in that, The x The preferred value range is 0.06 to 0.

15.

3. A method for preparing a high-electrostrain bismuth titanate sodium-based lead-free piezoelectric ceramic material as described in any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Weigh out Na source, Bi source, Ca source, Sr source, Ti source, Sn source and Sb source according to the stoichiometric ratio of the general formula of the chemical composition, mix them, ball mill and dry them to obtain mixed powder; S2. The mixed powder obtained in step S1 is pre-calcined to obtain pre-calcined powder; S3. The pre-fired powder obtained in step S2 is ball-milled, dried, and sieved to obtain ceramic powder. S4. The ceramic powder obtained in step S3 is granulated and shaped to obtain a green body. Then, the green body is debinded and sintered to obtain the high electrostriction sodium bismuth titanate-based lead-free piezoelectric ceramic material.

4. The preparation method according to claim 3, characterized in that, The Na source includes Na2CO3, the Bi source includes Bi2O3, the Ca source includes CaCO3, the Sr source includes SrCO3, the Ti source includes TiO2, the Sn source includes SnO2, and the Sb source includes Sb2O3.

5. The preparation method according to claim 3, characterized in that, In steps S1 and S3, the ball milling is a wet ball milling process, the ball milling medium includes anhydrous ethanol, the grinding balls include zirconia balls, and the ball milling speed is 200~400 rpm.

6. The preparation method according to claim 3, characterized in that, In step S2, the pre-firing temperature is 850℃~900℃, and the holding time is 2~4h.

7. The preparation method according to claim 3, characterized in that, In step S4, the molding pressure is 50~300MPa and the holding time is 3~5min.

8. The preparation method according to claim 3, characterized in that, In step S4, the glue discharge temperature is 500℃~600℃, and the heat preservation time is 1~2h.

9. The preparation method according to claim 3, characterized in that, In step S4, the sintering temperature is 1125℃~1225℃, and the holding time is 2~4h.

10. The application of a high electrostricted bismuth titanate sodium-based lead-free piezoelectric ceramic material as described in any one of claims 1 to 2 in the field of piezoelectric ceramics.

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