A lead-free piezoelectric ceramic material and its preparation method

Abstract

This invention discloses a lead-free piezoelectric ceramic material and its preparation method, belonging to the field of piezoelectric ceramic technology. The chemical formula of the lead-free piezoelectric ceramic material of this invention is (1-x)(0.7Bi). 1.04 FeO3-0.3BaTiO3)-x(Bi 0.5 Na 0.5 TiO3, where x is the mole fraction, x = 0.04. This invention utilizes the optimal doping of (Bi)O3. 0.5 Na 0.5 TiO3 effectively reduces the negative impact of Bi volatilization on performance, while improving the material's microstructure and inhibiting Fe... 3+ Converted to Fe 2+ This inhibits the formation of oxygen vacancies and reduces the oxygen vacancy concentration, ultimately giving piezoelectric ceramic materials excellent comprehensive electrical properties.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric ceramic technology and relates to a lead-free piezoelectric ceramic material and its preparation method. Background Technology

[0002] Piezoelectric ceramics have advantages such as low synthesis cost and excellent electromechanical coupling performance, enabling the mutual conversion of electrical energy and mechanical energy. Therefore, they are widely used as core components of electronic devices such as sensors, actuators and transducers.

[0003] Currently, Pb(Zr,Ti)O3 (PZT)-based ceramics have a large market share in practical applications due to their excellent piezoelectric properties at their quasi-isomorphic phase boundaries (MPB). However, PZT piezoelectric ceramics contain a significant amount of lead oxide in their raw materials, leading to substantial lead pollution that seriously harms the ecological environment and human health. Therefore, developing high-performance, lead-free piezoelectric ceramics that can replace PZT-based ceramics is of great importance.

[0004] With BaTiO3 (BTO) group, (K 0.5 Na 0.5 Compared to NbO3 (KNN)-based materials, lead-free BiFeO3 (BFO)-based materials exhibit superior ferroelectric properties, with a theoretical saturation polarization intensity reaching 100 μC / cm at room temperature. 2 The Curie temperature reaches 830℃. BFO-BTO ceramics have quasi-isomorphic phase boundaries (MPB) similar to those of PZT-based ceramics. At the same time, due to the introduction of BFO, a relatively high Curie temperature can be obtained. Therefore, BFO-BTO ceramics have high substitution potential for PZT-based ceramics.

[0005] However, the preparation of BiFeO3 requires a high synthesis temperature and is often accompanied by Bi 25 FeO 40 The presence of impurities such as Bi₂Fe₄O₉ is also present. Furthermore, during the preparation process, Bi is easily volatilized, forming Bi vacancies, and some Fe... 3+ Converted to Fe 2+ This leads to the generation of a large number of oxygen vacancies, resulting in defects such as large leakage current and high dielectric loss in BiFeO3-based ceramics.

[0006] Therefore, it is necessary to provide a lead-free piezoelectric ceramic material and its preparation method to reduce the leakage current of BiFeO3-based ceramics and improve their residual polarization intensity and other properties, thereby obtaining a BiFeO3-based lead-free piezoelectric ceramic material with excellent electrical properties. Summary of the Invention

[0007] To overcome the problems in the prior art, the present invention involves doping BFO-BTO ceramic with 0.04 molar fraction (Bi). 0.5 Na 0.5 TiO3 (BNT) is used as the third component to significantly reduce the oxygen vacancy concentration and leakage current density, and increase the residual polarization intensity and inverse piezoelectric constant, thus preparing lead-free piezoelectric ceramics with excellent electrical properties.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] This invention proposes a lead-free piezoelectric ceramic material, the chemical formula of which is 0.96 (0.7Bi). 1.04 FeO3-0.3BaTiO3)-0.04(Bi 0.5 Na 0.5 TiO3. Where 0.96, 0.7, 0.3, and 0.04 are all mole fractions, meaning that in lead-free piezoelectric ceramic materials, Bi... 1.04 The molar amount of FeO3 in Bi 1.04 The total molar amount of FeO3 and BaTiO3 is 0.7, and the molar amount of BaTiO3 accounts for 0.7% of Bi. 1.04 The total molar amount of FeO3 and BaTiO3 is 0.3, (Bi 0.5 Na 0.5 The molar amount of TiO3 accounts for 0.04% of the total molar amount of the piezoelectric ceramic material, and Bi... 1.04 The sum of the molar amounts of FeO3 and BaTiO3 accounts for 0.96% of the total molar amount of the piezoelectric ceramic material. Furthermore, since Bi readily reacts with oxygen at high temperatures to form Bi2O3 and volatilizes, creating Bi vacancies that affect the electrical properties of the piezoelectric ceramic material, the molar ratio of Bi to Fe is 1.04:1. Adding a slightly excess of Bi compensates for this Bi vacancy concentration.

[0010] Bi 1.04 The molar amount of FeO3 in Bi 1.04 The total molar amount of FeO3 and BaTiO3 is 0.7, and the molar amount of BaTiO3 accounts for 0.7% of Bi. 1.04 When the total molar amount of FeO3 and BaTiO3 is 0.3, the prepared ceramic has MPB, the highest relative density, the optimal grain size, and the best overall electrical properties.

[0011] Another aspect of the present invention provides a method for preparing the above-mentioned lead-free piezoelectric ceramic material, the method comprising the following steps:

[0012] (1) Weigh Bi(NO3)3·5H2O and Fe(NO3)3·9H2O according to the elemental molar ratio of Bi:Fe = 1.04:1. Dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O in an organic solvent. Then add additives to the solution, and stir, age, dry, grind, and pre-calcine the solution to obtain Bi. 1.04 FeO3 powder;

[0013] (2) Weigh C4H8BaO4 and C according to the elemental molar ratio of Ba:Ti = 1:1. 16 H 36 O4Ti, C4H8BaO4, C 16 H 36 O4Ti is dissolved in an organic solvent, and then the solution is stirred, aged, dried, ground and pre-calcined in sequence to obtain BaTiO3 powder;

[0014] (3) Weigh Bi(NO3)3·5H2O, C2H3NaO2, and C according to the elemental molar ratio of Bi:Na:Ti = 0.5:0.5:1. 16 H 36 O4Ti, Bi(NO3)3·5H2O, C2H3NaO2, C 16 H 36 O4Ti was dissolved in an organic solvent, and then the solution was subjected to stirring, aging, drying, grinding, and pre-calcination in sequence to obtain (Bi). 0.5 Na 0.5 )TiO3 powder;

[0015] (4) Using the Bi prepared in step (1) 1.04 FeO3 powder, BaTiO3 powder prepared in step (2), and (Bi) powder prepared in step (3) 0.5 Na 0.5 TiO3 powder was used as raw material. The raw material was weighed according to the stoichiometric ratio and then subjected to ball milling, drying, pre-calcination, secondary ball milling, and secondary drying in sequence to obtain a uniformly mixed powder.

[0016] (5) The mixed powder obtained in step (4) is granulated, shaped, debinded, sintered, and then cooled in the furnace to obtain ceramic sheets. The ceramic sheets are then silver-plated and polarized to obtain lead-free piezoelectric ceramic materials.

[0017] Preferably, in step (1), the organic solvent is a mixed liquid of C3H8O2 and C2H4O2, wherein the volume ratio of C3H8O2 to C2H4O2 is C3H8O2:C2H4O2 = 3:1, and the additives include dispersant (CH2OH)2, stabilizer C2H7NO, and chelating agent C6H8O7·H2O. The molar ratio of the added (CH2OH)2 to the molar ratio of the metal cation in the solution is (CH2OH)2:metal cation = 1:1, the molar ratio of the added C2H7NO to the molar ratio of the metal cation in the solution is C2H7NO:metal cation = 1:1, and the molar ratio of the added C6H8O7·H2O to the molar ratio of the metal cation in the solution is C6H8O7·H2O:metal cation = 1.15:1.

[0018] In step (2), the organic solvent is a mixed liquid of C2H4O2 and C2H5OH, wherein the volume ratio of C2H4O2 to C2H5OH is C2H4O2:C2H5OH = 4:1;

[0019] In step (3), the organic solvent is a mixture of (CH2OH)2 and C2H4O2, wherein the volume ratio of (CH2OH)2 to C2H4O2 is (CH2OH)2:C2H4O2 = 4:1.

[0020] Preferably, in step (1), the solution is stirred at room temperature for 24 hours;

[0021] In step (2), the mixed liquid is stirred at 60°C for 4 to 6 hours;

[0022] In step (3), the mixed body fluid is stirred at 60°C for 2-3 hours.

[0023] Preferably, in steps (1) and (2), the aging time is 48 hours, the drying temperature is 85°C, and the drying time is 48 hours.

[0024] In step (3), the aging time is 72 hours, the drying temperature is 85°C, and the drying time is 7 days.

[0025] Preferably, in step (1), the pre-calcination process is as follows: the ground material is heated to 550°C at a heating rate of 5±0.5°C / min and kept at that temperature for 4 hours;

[0026] In step (2), the specific process of pre-calcination is as follows: the ground material is heated to 1000℃ at a heating rate of 5±0.5℃ / min and kept at that temperature for 2 hours;

[0027] In step (3), the specific process of pre-calcination is as follows: the ground material is heated to 650°C at a heating rate of 5±0.5°C / min and kept at that temperature for 2 hours.

[0028] Preferably, in step (4), the ball milling media are both anhydrous ethanol, the ball-to-material ratio is 2.2:1, the ball milling speed is 160 rpm, the ball milling time is 24 h, and the pre-calcination process is as follows: the material after the first drying is heated to 800 ℃ at a heating rate of 5 ± 0.5 ℃ / min and kept at that temperature for 2 h.

[0029] Preferably, in step (5), the binder used for granulation is a 5% (w / w) polyvinyl alcohol aqueous solution, and the molding process is as follows: the granulated product is pressed into a ceramic blank under a pressure of 2 to 10 MPa.

[0030] As a preferred embodiment, the specific process of debinding in step (5) is as follows: the ceramic blank obtained by molding is heated to 600℃ at a heating rate of 5±0.5℃ / min and held for 3h. The sintering adopts a two-step sintering method. First, the material after debinding is sintered at 1025℃ for 30min. Then, the temperature is reduced to 900℃ and sintered for another 90min.

[0031] Preferably, in step (5), the polarization process is as follows: the ceramic sheet is sandwiched between the positive and negative electrodes and immersed in silicone oil at 120±5℃. Then, the positive and negative electrodes are energized and the voltage is maintained at 40~50kV / cm. The polarization time is 30±1min.

[0032] The beneficial effects of this invention are:

[0033] 1. The remanent polarization P of the piezoelectric ceramic material prepared by this invention r It can reach 33.39 μC / cm 2 The leakage current density J can reach 1.94 × 10⁻⁶. -5 A / cm 2 Inverse piezoelectric constant It can reach 173.9 pm / V.

[0034] 2. This invention prepares Bi by adding an excess of Bi element. 1.04 FeO3 powder is used to compensate for the volatilization of Bi element during the preparation process, thereby reducing the impact of Bi volatilization on the performance of ceramic materials.

[0035] 3. The preparation method of the present invention has good controllability, can form nano-sized particles with good particle uniformity, which helps to improve the performance of the prepared piezoelectric ceramics.

[0036] 4. The preparation conditions of this invention are simple and easy to operate. It does not require additional conditions such as high temperature and high pressure, atmosphere, quenching, etc., and has good repeatability and stability.

[0037] 5. The piezoelectric ceramic material of this invention has excellent substitution potential for PZT-based ceramics, effectively avoiding environmental pollution and health hazards caused by lead oxide. Attached Figure Description

[0038] Figure 1 Figure 1 shows the SEM images of the piezoelectric ceramic materials prepared in Examples 1 and 1-5 of the present invention. Figure 2 shows the SEM images of the piezoelectric ceramic materials prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5.

[0039] Figure 2 The figures shown are XPS measurement spectra of the piezoelectric ceramic materials prepared in Examples 1 and 1-5 of the present invention. Figure (a) is the XPS measurement spectrum of the Fe 2p nuclear level, and Figure (b) is the XPS measurement spectrum of the O1s nuclear level. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0041] In the embodiments and comparative examples of this invention, unless otherwise specified, commercially available analytical grade chemical reagents were used in the experiments.

[0042] Example 1

[0043] In this embodiment, x = 0.04, and lead-free piezoelectric ceramic materials are prepared according to the following steps:

[0044] (1) Weigh Bi(NO3)3·5H2O and Fe(NO3)3·9H2O according to the elemental molar ratio Bi:Fe = 1.04:1. Dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O in a mixed liquid with a volume ratio of C3H8O2:C2H4O2 = 3:1, and stir to dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O. After dissolution, add (CH2OH)2, C2H7NO, and C6H8O7·H2O to the solution, and stir the solution at room temperature for 24 hours. Then, age the solution under light-protected conditions for 48 hours, and then dry the solution at 85℃ for 48 hours to obtain a solid substance. Grind the solid substance into powder, and then heat the powder to 550℃ at a heating rate of 5±0.5℃ / min and hold for 4 hours to remove volatile impurities, to obtain Bi. 1.04 FeO3 powder.

[0045] (2) Weigh C4H8BaO4 and C according to the elemental molar ratio of Ba:Ti = 1:1. 16 H 36 O4Ti. Combine C4H8BaO4, C 16 H 36 O4Ti dissolved in a volume ratio of C4H8BaO4:C 16 H 36 In a mixed liquid of O4Ti = 4:1, the solution was stirred at 60℃ for 5 hours, then aged in the dark for 48 hours, and then dried at 85℃ for 48 hours to obtain a solid substance. The solid substance was ground into powder, and then heated to 1000℃ at a heating rate of 5±0.5℃ / min and held for 2 hours to remove volatile impurities, thus obtaining BaTiO3 powder.

[0046] (3) Weigh Bi(NO3)3·5H2O, C2H3NaO2, and C according to the elemental molar ratio of Bi:Na:Ti = 0.5:0.5:1. 16 H 36 O4Ti. Combine Bi(NO3)3·5H2O, C2H3NaO2, C 16 H 36 O4Ti dissolves in (CH2OH)2 by volume:

[0047] In a C2H4O2 = 4:1 mixed liquid, the solution was stirred at 60℃ for 2.5 h, then aged under light-protected conditions for 72 h, and then dried at 85℃ for 7 days to obtain a solid substance. The solid substance was ground into powder, and then heated to 650℃ at a heating rate of 5±0.5℃ / min and held at that temperature for 2 h to remove volatile impurities, yielding (Bi) 0.5 Na 0.5 TiO3 powder.

[0048] (4) Using Bi 1.04 FeO3 powder, BaTiO3 powder, (Bi 0.5 Na 0.5 TiO3 powder was used as a raw material, according to the chemical formula 0.96 (0.7Bi) 1.04 FeO3-0.3BaTiO3)-0.04(Bi 0.5 Na 0.5The TiO3 powder raw material was weighed according to the stoichiometric ratio. Anhydrous ethanol was used as the milling medium, and agate balls were selected as the milling beads. The mixture was prepared at a mass ratio of raw material:agate balls:ethanol = 1:2.2:2.4 and ball-milled at 160 rpm for 24 hours. After milling, the powder was dried. The dried material was then heated to 800℃ at a heating rate of 5 ± 0.5℃ / min and held at that temperature for 2 hours for pre-calcination to improve powder uniformity and allow the reaction to obtain the main crystalline phase. The pre-calcined powder was then ball-milled again under the same conditions as before, and dried to obtain a mixed powder.

[0049] (5) The mixed powder was granulated using a granulator. During the granulation process, a 5% (w / w) polyvinyl alcohol aqueous solution was added as a binder. After granulation, the granulated product was sieved. The sieved material was added to a pressing mold and pressed sequentially at 2 MPa for 2 min, 4 MPa for 3 min, 6 MPa for 3 min, 8 MPa for 5 min, and 10 MPa for 5 min to obtain a ceramic green body with a diameter of 10 mm and a thickness of 1 mm. The ceramic green body was heated to 600 °C at a heating rate of 5 ± 0.5 °C / min and held for 3 h to remove the binder. Then, the ceramic green body was heated to 1025 °C at a heating rate of 5 ± 0.5 °C / min and sintered for 30 min. Then, the ceramic green body was cooled to 900 °C and sintered for 90 min. Finally, it was cooled to room temperature in the furnace to obtain ceramic sheets. A ceramic sheet was polished into a smooth sheet with a thickness of approximately 0.4 mm. Silver paste was screen-printed on both sides, and the sheet was fired at 550℃ for 15 min. Finally, the ceramic sheet was sandwiched between the positive and negative electrodes and immersed in silicone oil at 120±5℃, and polarized at a DC voltage of 45 kV / cm for 30 min. A lead-free piezoelectric ceramic material was thus prepared.

[0050] The piezoelectric ceramic material prepared in this embodiment was subjected to SEM testing, and the results are as follows: Figure 1 As shown.

[0051] XPS testing was performed on the piezoelectric ceramic material prepared in this embodiment, and the results are as follows: Figure 2 As shown.

[0052] The electrical properties of the piezoelectric ceramic material prepared in this embodiment were tested, and the results are shown in Table 1.

[0053] Example 2

[0054] This embodiment prepares lead-free piezoelectric ceramic materials according to the following steps:

[0055] (1) Weigh Bi(NO3)3·5H2O and Fe(NO3)3·9H2O according to the elemental molar ratio Bi:Fe = 1.04:1. Dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O in a mixed liquid with a volume ratio of C3H8O2:C2H4O2 = 3:1, and stir to dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O. After dissolution, add (CH2OH)2, C2H7NO, and C6H8O7·H2O to the solution, and stir the solution at room temperature for 24 hours. Then, age the solution under light-protected conditions for 48 hours, and then dry the solution at 85℃ for 48 hours to obtain a solid substance. Grind the solid substance into powder, and then heat the powder to 550℃ at a heating rate of 5±0.5℃ / min and hold for 4 hours to remove volatile impurities, to obtain Bi. 1.04 FeO3 powder.

[0056] (2) Weigh C4H8BaO4 and C according to the elemental molar ratio of Ba:Ti = 1:1. 16 H 36 O4Ti. Combine C4H8BaO4, C 16 H 36 O4Ti dissolved in a volume ratio of C4H8BaO4:C 16 H 36 In a mixed liquid of O4Ti = 4:1, the solution was stirred at 60℃ for 4 hours, then aged in the dark for 48 hours, and then dried at 85℃ for 48 hours to obtain a solid substance. The solid substance was ground into powder, and then heated to 1000℃ at a heating rate of 5±0.5℃ / min and held for 2 hours to remove volatile impurities, thus obtaining BaTiO3 powder.

[0057] (3) Weigh Bi(NO3)3·5H2O, C2H3NaO2, and C according to the elemental molar ratio of Bi:Na:Ti = 0.5:0.5:1. 16 H 36 O4Ti. Combine Bi(NO3)3·5H2O, C2H3NaO2, C 16 H 36 O4Ti dissolves in (CH2OH)2 by volume:

[0058] In a C2H4O2 = 4:1 mixed liquid, the solution was stirred at 60℃ for 2 hours, then aged in the dark for 72 hours, and then dried at 85℃ for 7 days to obtain a solid substance. The solid substance was ground into powder, and then heated to 650℃ at a heating rate of 5±0.5℃ / min and held at that temperature for 2 hours to remove volatile impurities, yielding (Bi) 0.5 Na 0.5TiO3 powder.

[0059] (4) Using Bi 1.04 FeO3 powder, BaTiO3 powder, (Bi 0.5 Na 0.5 TiO3 powder was used as a raw material, according to the chemical formula 0.96 (0.7Bi) 1.04 FeO3-0.3BaTiO3)-0.04(Bi 0.5 Na 0.5 The TiO3 powder raw material was weighed according to the stoichiometric ratio. Anhydrous ethanol was used as the milling medium, and agate balls were selected as the milling beads. The mixture was prepared at a mass ratio of raw material:agate balls:ethanol = 1:2.2:2.4 and ball-milled at 160 rpm for 24 hours. After milling, the powder was dried. The dried material was then heated to 800℃ at a heating rate of 5 ± 0.5℃ / min and held at that temperature for 2 hours for pre-calcination to improve powder uniformity and allow the reaction to obtain the main crystalline phase. The pre-calcined powder was then ball-milled again under the same conditions as before, and dried to obtain a mixed powder.

[0060] (5) The mixed powder was granulated using a granulator. During the granulation process, a 5% (w / w) polyvinyl alcohol aqueous solution was added as a binder. After granulation, the granulated product was sieved. The sieved material was added to a pressing mold and pressed sequentially at 2 MPa for 2 min, 4 MPa for 3 min, 6 MPa for 3 min, 8 MPa for 5 min, and 10 MPa for 5 min to obtain a ceramic green body with a diameter of 10 mm and a thickness of 1 mm. The ceramic green body was heated to 600 °C at a heating rate of 5 ± 0.5 °C / min and held for 3 h to remove the binder. Then, the ceramic green body was heated to 1025 °C at a heating rate of 5 ± 0.5 °C / min and sintered for 30 min. Then, the ceramic green body was cooled to 900 °C and sintered for 90 min. Finally, it was cooled to room temperature in the furnace to obtain ceramic sheets. A ceramic sheet was polished into a smooth sheet with a thickness of approximately 0.4 mm. Silver paste was screen-printed on both sides, and the sheet was fired at 550℃ for 15 min. Finally, the ceramic sheet was sandwiched between the positive and negative electrodes and immersed in silicone oil at 120±5℃, and polarized at a DC voltage of 40 kV / cm for 30 min. A lead-free piezoelectric ceramic material was thus prepared.

[0061] The piezoelectric ceramic material prepared in this embodiment has similar properties to the piezoelectric ceramic material in Example 1.

[0062] Example 3

[0063] This embodiment prepares lead-free piezoelectric ceramic materials according to the following steps:

[0064] (1) Weigh Bi(NO3)3·5H2O and Fe(NO3)3·9H2O according to the elemental molar ratio Bi:Fe = 1.04:1. Dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O in a mixed liquid with a volume ratio of C3H8O2:C2H4O2 = 3:1, and stir to dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O. After dissolution, add (CH2OH)2, C2H7NO, and C6H8O7·H2O to the solution, and stir the solution at room temperature for 24 hours. Then, age the solution under light-protected conditions for 48 hours, and then dry the solution at 85℃ for 48 hours to obtain a solid substance. Grind the solid substance into powder, and then heat the powder to 550℃ at a heating rate of 5±0.5℃ / min and hold for 4 hours to remove volatile impurities, to obtain Bi. 1.04 FeO3 powder.

[0065] (2) Weigh C4H8BaO4 and C according to the elemental molar ratio of Ba:Ti = 1:1. 16 H 36 O4Ti. Combine C4H8BaO4, C 16 H 36 O4Ti dissolved in a volume ratio of C4H8BaO4:C 16 H 36 In a mixed liquid of O4Ti = 4:1, the solution was stirred at 60℃ for 6 hours, then aged in the dark for 48 hours, and then dried at 85℃ for 48 hours to obtain a solid substance. The solid substance was ground into powder, and then heated to 1000℃ at a heating rate of 5±0.5℃ / min and held for 2 hours to remove volatile impurities, thus obtaining BaTiO3 powder.

[0066] (3) Weigh Bi(NO3)3·5H2O, C2H3NaO2, and C according to the elemental molar ratio of Bi:Na:Ti = 0.5:0.5:1. 16 H 36 O4Ti. Combine Bi(NO3)3·5H2O, C2H3NaO2, C 16 H 36 O4Ti dissolves in (CH2OH)2 by volume:

[0067] In a C2H4O2 = 4:1 mixed liquid, the solution was stirred at 60℃ for 3 hours, then aged in the dark for 72 hours, and then dried at 85℃ for 7 days to obtain a solid substance. The solid substance was ground into powder, and then heated to 650℃ at a heating rate of 5±0.5℃ / min and held at that temperature for 2 hours to remove volatile impurities, yielding (Bi) 0.5 Na 0.5TiO3 powder.

[0068] (4) Using Bi 1.04 FeO3 powder, BaTiO3 powder, (Bi 0.5 Na 0.5 TiO3 powder was used as a raw material, according to the chemical formula 0.96 (0.7Bi) 1.04 FeO3-0.3BaTiO3)-0.04(Bi 0.5 Na 0.5 The TiO3 powder raw material was weighed according to the stoichiometric ratio. Anhydrous ethanol was used as the milling medium, and agate balls were selected as the milling beads. The mixture was prepared at a mass ratio of raw material:agate balls:ethanol = 1:2.2:2.4 and ball-milled at 160 rpm for 24 hours. After milling, the powder was dried. The dried material was then heated to 800℃ at a heating rate of 5 ± 0.5℃ / min and held at that temperature for 2 hours for pre-calcination to improve powder uniformity and allow the reaction to obtain the main crystalline phase. The pre-calcined powder was then ball-milled again under the same conditions as before, and dried to obtain a mixed powder.

[0069] (5) The mixed powder was granulated using a granulator. During the granulation process, a 5% (w / w) polyvinyl alcohol aqueous solution was added as a binder. After granulation, the granulated product was sieved. The sieved material was added to a pressing mold and pressed sequentially at 2 MPa for 2 min, 4 MPa for 3 min, 6 MPa for 3 min, 8 MPa for 5 min, and 10 MPa for 5 min to obtain a ceramic green body with a diameter of 10 mm and a thickness of 1 mm. The ceramic green body was heated to 600 °C at a heating rate of 5 ± 0.5 °C / min and held for 3 h to remove the binder. Then, the ceramic green body was heated to 1025 °C at a heating rate of 5 ± 0.5 °C / min and sintered for 30 min. Then, the ceramic green body was cooled to 900 °C and sintered for 90 min. Finally, it was cooled to room temperature in the furnace to obtain ceramic sheets. A ceramic sheet was polished into a smooth sheet with a thickness of approximately 0.4 mm. Silver paste was screen-printed on both sides, and the sheet was fired at 550℃ for 15 min. Finally, the ceramic sheet was sandwiched between the positive and negative electrodes and immersed in silicone oil at 120±5℃, and polarized at a DC voltage of 50 kV / cm for 30 min. A lead-free piezoelectric ceramic material was thus prepared.

[0070] The piezoelectric ceramic material prepared in this embodiment has similar properties to the piezoelectric ceramic material in Example 1.

[0071] Comparative Example 1

[0072] This comparative example uses the same method as Example 1 to prepare lead-free piezoelectric ceramic materials, except that in this comparative example, x = 0.

[0073] The piezoelectric ceramic material prepared in this comparative example was subjected to SEM testing, and the results are as follows: Figure 1 As shown.

[0074] XPS tests were performed on the piezoelectric ceramic material prepared in this comparative example, and the results are as follows: Figure 2 As shown.

[0075] The electrical properties of the piezoelectric ceramic material prepared in this comparative example were tested, and the results are shown in Table 1.

[0076] Comparative Example 2

[0077] This comparative example uses the same method as Example 1 to prepare lead-free piezoelectric ceramic materials, except that in this comparative example, x = 0.02.

[0078] The piezoelectric ceramic material prepared in this comparative example was subjected to SEM testing, and the results are as follows: Figure 1 As shown.

[0079] XPS tests were performed on the piezoelectric ceramic material prepared in this comparative example, and the results are as follows: Figure 2 As shown.

[0080] The electrical properties of the piezoelectric ceramic material prepared in this comparative example were tested, and the results are shown in Table 1.

[0081] Comparative Example 3

[0082] This comparative example uses the same method as Example 1 to prepare lead-free piezoelectric ceramic materials, except that in this comparative example, x = 0.06.

[0083] The piezoelectric ceramic material prepared in this comparative example was subjected to SEM testing, and the results are as follows: Figure 1 As shown.

[0084] XPS tests were performed on the piezoelectric ceramic material prepared in this comparative example, and the results are as follows: Figure 2 As shown.

[0085] The electrical properties of the piezoelectric ceramic material prepared in this comparative example were tested, and the results are shown in Table 1.

[0086] Comparative Example 4

[0087] This comparative example uses the same method as Example 1 to prepare lead-free piezoelectric ceramic materials, except that in this comparative example, x = 0.08.

[0088] The piezoelectric ceramic material prepared in this comparative example was subjected to SEM testing, and the results are as follows: Figure 1 As shown.

[0089] XPS tests were performed on the piezoelectric ceramic material prepared in this comparative example, and the results are as follows: Figure 2As shown.

[0090] The electrical properties of the piezoelectric ceramic material prepared in this comparative example were tested, and the results are shown in Table 1.

[0091] Comparative Example 5

[0092] This comparative example uses the same method as Example 1 to prepare lead-free piezoelectric ceramic materials, except that in this comparative example, x = 0.10.

[0093] The piezoelectric ceramic material prepared in this comparative example was subjected to SEM testing, and the results are as follows: Figure 1 As shown.

[0094] XPS tests were performed on the piezoelectric ceramic material prepared in this comparative example, and the results are as follows: Figure 2 As shown.

[0095] The electrical properties of the piezoelectric ceramic material prepared in this comparative example were tested, and the results are shown in Table 1.

[0096] Table 1

[0097]

[0098] As shown in Table 1, compared with Comparative Examples 1-5, Example 1 exhibits the highest remanent polarization, lowest leakage current density, highest inverse piezoelectric constant, and highest relative density. This indicates that Example 1 possesses the best piezoelectric performance compared to Comparative Examples 1-5. Furthermore, the high remanent polarization and low leakage current density suggest that the piezoelectric ceramic material of Example 1 possesses not only excellent piezoelectric properties but also excellent ferroelectric properties. Compared to Comparative Examples 2-4, although the increase in remanent polarization and the decrease in leakage current density in Example 1 are limited, the inverse piezoelectric constant of Example 1 is significantly improved. Compared to Comparative Example 1, the increase in the inverse piezoelectric constant of Example 1 is limited, but its remanent polarization and leakage current density are significantly improved. Therefore, the value of x significantly affects the overall electrical properties (piezoelectric and ferroelectric properties) of the piezoelectric ceramic material. Only when x = 0.04 is the overall electrical performance of the piezoelectric ceramic material optimal; changing the value of x significantly reduces the overall performance of the piezoelectric ceramic material.

[0099] pass Figure 1 It can be seen that the piezoelectric ceramic materials of Example 1 and Comparative Examples 1-5 have relatively dense microstructures, but some pores still exist. The formation of pores may be due to the volatilization of Bi ions, which fully demonstrates that Bi ions will volatilize during the preparation process. Therefore, it is necessary to compensate for Bi ions to reduce pore formation and improve the density of the microstructure of the piezoelectric ceramic materials. Figure 1It can also be seen that when the value of x increases from 0 to 0.04, the average grain size of the piezoelectric ceramic material decreases significantly. This may be due to the relatively low molar fraction of BNT doping, which can effectively pin grain boundaries and limit grain growth. Thus, as the BNT content increases, the overall electrical performance of the piezoelectric ceramic material is improved to a certain extent. However, compared with Comparative Example 1, the inverse piezoelectric constant of Comparative Example 2 is significantly reduced, indicating that the average grain size needs to be maintained at an appropriate level for piezoelectric ceramic materials. Too fine or too coarse grains will have a significant negative impact on the overall electrical performance of the piezoelectric ceramic material. As the BNT doping amount further increases, the refinement of the average grain size slows down. This may be because the effect of the tertiary component in the doping is close to saturation or the grain boundary migration resistance reaches its limit. As a result, the beneficial effect of the refinement of the average grain size is weakened, while the negative impact caused by excessively fine grains is aggravated, showing a more obvious negative impact on the overall electrical performance of the piezoelectric ceramic material.

[0100] pass Figure 2 (a) It can be seen that in Example 1, Fe 3+ / Fe 2+ The peak area ratio was 69.2:30.8, while in Comparative Examples 1-5, Fe... 3+ / Fe 2+ The peak area ratios were 42.6:57.4, 44.7:55.3, 49.5:50.5, 47.6:52.4, and 39.2:60.8, respectively, which fully demonstrates that the piezoelectric ceramic material prepared by this invention effectively suppresses Fe 3+ Converted to Fe 2+ , and through Figure 2 (b) It can be seen that the oxygen vacancy concentration in Example 1 is 30.7%, while in Comparative Examples 1-5, the oxygen vacancy concentrations are 45.1%, 35.8%, 40.8%, 42.4% and 43.5% respectively. This fully demonstrates that the piezoelectric ceramic material prepared by the present invention can effectively reduce the oxygen vacancy concentration, thereby reducing the leakage current density and improving the overall electrical performance of the piezoelectric ceramic material.

[0101] In summary, the piezoelectric ceramic material of this invention can effectively reduce the negative impact of Bi volatilization on performance, while improving the material's microstructure and suppressing Fe volatilization. 3+ Converted to Fe 2+ This inhibits the formation of oxygen vacancies and reduces the oxygen vacancies concentration, ultimately giving piezoelectric ceramic materials excellent comprehensive electrical properties.

[0102] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A lead-free piezoelectric ceramic material, characterized in that: The chemical formula for the lead-free piezoelectric ceramic material is (1-x)(0.7Bi). 1.04 FeO3-0.3BaTiO3)-x(Bi 0.5 Na 0.5 TiO3, where x is the mole fraction, x = 0.

04.

2. The method for preparing a lead-free piezoelectric ceramic material according to claim 1, characterized in that: The preparation method includes the following steps: (1) Weigh Bi(NO3)3·5H2O and Fe(NO3)3·9H2O according to the elemental molar ratio of Bi:Fe = 1.04:

1. Dissolve Bi(NO3)3·5H2O and Fe(NO3)3·9H2O in an organic solvent. Then add additives to the solution, and stir, age, dry, grind, and pre-calcine the solution to obtain Bi. 1.04 FeO3 powder; (2) Weigh C4H8BaO4 and C according to the elemental molar ratio of Ba:Ti = 1:

1. 16 H 36 O4Ti, C4H8BaO4, C 16 H 36 O4Ti is dissolved in an organic solvent, and then the solution is stirred, aged, dried, ground and pre-calcined in sequence to obtain BaTiO3 powder; (3) Weigh Bi(NO3)3·5H2O, C2H3NaO2, and C according to the elemental molar ratio of Bi:Na:Ti = 0.5:0.5:

1. 16 H 36 O4Ti, Bi(NO3)3·5H2O, C2H3NaO2, C 16 H 36 O4Ti was dissolved in an organic solvent, and then the solution was subjected to stirring, aging, drying, grinding, and pre-calcination in sequence to obtain (Bi). 0.5 Na 0.5 )TiO3 powder; (4) Using the Bi prepared in step (1) 1.04 FeO3 powder, BaTiO3 powder prepared in step (2), and (Bi) powder prepared in step (3) 0.5 Na 0.5 TiO3 powder was used as raw material. The raw material was weighed according to the stoichiometric ratio and then subjected to ball milling, drying, pre-calcination, secondary ball milling, and secondary drying in sequence to obtain a uniformly mixed powder. (5) The mixed powder obtained in step (4) is granulated, shaped, debinded, sintered, and then cooled in the furnace to obtain ceramic sheets. The ceramic sheets are then silver-plated and polarized to obtain lead-free piezoelectric ceramic materials.

3. The preparation method according to claim 2, characterized in that: In step (1), the organic solvent is a mixed liquid of C3H8O2 and C2H4O2, wherein the volume ratio of C3H8O2 to C2H4O2 is C3H8O2:C2H4O2 = 3:

1. The additives include dispersant (CH2OH)2, stabilizer C2H7NO, and chelating agent C6H8O7·H2O. The molar ratio of the added (CH2OH)2 to the molar ratio of the metal cation in the solution is (CH2OH)2:metal cation = 1:

1. The molar ratio of the added C2H7NO to the molar ratio of the metal cation in the solution is C2H7NO:metal cation = 1:

1. The molar ratio of the added C6H8O7·H2O to the molar ratio of the metal cation in the solution is C6H8O7·H2O:metal cation = 1.15:

1. In step (2), the organic solvent is a mixed liquid of C2H4O2 and C2H5OH, wherein the volume ratio of C2H4O2 to C2H5OH is C2H4O2:C2H5OH = 4:1; In step (3), the organic solvent is a mixture of (CH2OH)2 and C2H4O2, wherein the volume ratio of (CH2OH)2 to C2H4O2 is (CH2OH)2:C2H4O2 = 4:

1.

4. The preparation method according to claim 2, characterized in that: In step (1), the solution is stirred at room temperature for 24 hours; In step (2), the mixed liquid is stirred at 60°C for 4 to 6 hours; In step (3), the mixed body fluid is stirred at 60°C for 2-3 hours.

5. The preparation method according to claim 2, characterized in that: In steps (1) and (2), the aging time is 48 hours, the drying temperature is 85°C, and the drying time is 48 hours. In step (3), the aging time is 72 hours, the drying temperature is 85°C, and the drying time is 7 days.

6. The preparation method according to claim 2, characterized in that: In step (1), the specific process of pre-calcination is as follows: the ground material is heated to 550°C at a heating rate of 5±0.5°C / min and kept at that temperature for 4 hours; In step (2), the specific process of pre-calcination is as follows: the ground material is heated to 1000℃ at a heating rate of 5±0.5℃ / min and kept at that temperature for 2 hours; In step (3), the specific process of pre-calcination is as follows: the ground material is heated to 650°C at a heating rate of 5±0.5°C / min and kept at that temperature for 2 hours.

7. The preparation method according to claim 2, characterized in that: In step (4), the ball milling media in both steps are anhydrous ethanol, the ball-to-material ratio is 2.2:1, the ball milling speed is 160 rpm, and the ball milling time is 24 h. The specific pre-calcination process is as follows: the material after the first drying is heated to 800 ℃ at a heating rate of 5 ± 0.5 ℃ / min and kept at that temperature for 2 h.

8. The preparation method according to claim 2, characterized in that: In step (5), the binder used for granulation is a 5% polyvinyl alcohol aqueous solution. The specific molding process is as follows: the granulated product is pressed sequentially under a pressure of 2MPa for 2 minutes, under a pressure of 4MPa for 3 minutes, under a pressure of 6MPa for 3 minutes, under a pressure of 8MPa for 5 minutes, and under a pressure of 10MPa for 5 minutes, and finally pressed into a ceramic blank.

9. The preparation method according to claim 2, characterized in that: The specific process of debinding in step (5) is as follows: the ceramic blank obtained by molding is heated to 600℃ at a heating rate of 5±0.5℃ / min and held for 3h. The sintering adopts a two-step sintering method. First, the material after debinding is sintered at 1025℃ for 30min. Then, the temperature is reduced to 900℃ and sintered for another 90min.

10. The preparation method according to claim 2, characterized in that: In step (5), the specific polarization process is as follows: the ceramic sheet is sandwiched between the positive and negative electrodes and immersed in silicone oil at 120±5℃. Then, the positive and negative electrodes are energized and the voltage is maintained at 40~50kV / cm. The polarization time is 30±1min.

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