Lead-free piezoelectric ceramic material and preparation method thereof

Abstract

The invention discloses a lead-free piezoelectric ceramic material and a preparation method thereof, and belongs to the technical field of piezoelectric ceramics. The chemical expression of the lead-free piezoelectric ceramic material disclosed by the invention is (1-x) (0.7 Bi < 1.04 > FeO < 3 >-0.3 BaTiO < 3 >)-x (Bi < 0.5 > Na < 0.5 >) TiO < 3 >, and x is molar fraction and is equal to 0.04. The most suitable (Bi0. 5Na0. 5) TiO3 is doped, so that the negative influence of Bi volatilization on the performance is effectively reduced, meanwhile, the microscopic structure of the material is improved, Fe < 3 + > is inhibited from being converted into Fe < 2 + >, the formation of oxygen vacancies is inhibited, the concentration of the oxygen vacancies is reduced, and finally, the piezoelectric ceramic material has excellent comprehensive electrical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of piezoelectric ceramics and relates to a lead-free piezoelectric ceramic material and a preparation method thereof. Background Art

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

[0003] At present, due to the Pb(Zr,Ti)O 3 (PZT for short) based ceramics have very excellent piezoelectric properties at their quasi-modular phase boundary (MPB), so PZT based ceramics account for a large proportion in current practical applications. However, there is a lot of lead oxide in the raw materials of PZT piezoelectric ceramics, which will produce a large amount of lead pollution, seriously endangering the ecological environment and human health. Therefore, it is of great significance to develop high-performance lead-free piezoelectric ceramics that can replace PZT based ceramics.

[0004] With BaTiO 3 (BTO for short) base, (K 0.5 Na 0.5 )NbO 3 Compared with lead-free BiFeO 3 (BFO)-based materials exhibit excellent ferroelectric properties, with a theoretical saturation polarization intensity of 100 μC / cm at room temperature. 2 , the Curie temperature reaches 830°C. BFO-BTO ceramics have a morphotropic phase boundary (MPB) similar to that 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 a high potential to replace PZT-based ceramics.

[0005] However, BiFeO 3 During the preparation process, a higher synthesis temperature is required, and it is often accompanied by Bi 25 FeO 40 and Bi 2 Fe 4 O 9 At the same time, during the preparation process, Bi is easily volatilized to form Bi vacancies, and part of Fe 3+ Converted to Fe 2+ , resulting in a large number of oxygen vacancies, which in turn causes BiFeO 3 The base ceramic has defects such as large leakage current and high dielectric loss.

[0006] Therefore, it is necessary to provide a lead-free piezoelectric ceramic material and a preparation method thereof to reduce BiFeO 3The leakage current of the base ceramic is reduced, and its residual polarization strength and other properties are improved, so as to obtain BiFeO with excellent electrical properties. 3 Based on lead-free piezoelectric ceramic materials. Summary of the invention

[0007] In order to overcome the problems in the background technology, the present invention doped 0.04 mole fraction of (Bi 0.5 Na 0.5 )TiO 3 (BNT for short) as the third component significantly reduces the oxygen vacancy concentration and leakage current density, and increases the residual polarization strength and inverse piezoelectric constant, thereby preparing lead-free piezoelectric ceramics with excellent electrical properties.

[0008] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0009] In one aspect, the present invention provides a lead-free piezoelectric ceramic material, wherein the chemical formula of the lead-free piezoelectric ceramic material is 0.96 (0.7Bi 1.04 FeO 3 -0.3BaTiO 3 )-0.04(Bi 0.5 Na 0.5 )TiO 3 0.96, 0.7, 0.3, and 0.04 are all molar fractions, that is, in lead-free piezoelectric ceramic materials, Bi 1.04 FeO 3 The molar amount of Bi 1.04 FeO 3 、BaTiO 3 The total molar amount is 0.7, BaTiO 3 Molar amount accounts for Bi 1.04 FeO 3 、BaTiO 3 The total molar amount is 0.3, (Bi 0.5 Na 0.5 )TiO 3 The molar amount accounts for 0.04 of the total molar amount of piezoelectric ceramic materials. 1.04 FeO 3 、BaTiO 3 The total molar amount accounts for 0.96 of the total molar amount of the piezoelectric ceramic material. In addition, since the Bi element easily reacts with oxygen under high temperature conditions to form Bi 2 O 3 However, volatilization produces Bi vacancies, which affect the electrical properties of piezoelectric ceramic materials. Therefore, the molar ratio of Bi element to Fe element is 1.04:1. By adding a slightly excess Bi element to achieve Bi element compensation, it is beneficial to reduce the Bi vacancy concentration.

[0010] Bi 1.04 FeO 3 The molar amount of Bi 1.04 FeO 3 、BaTiO 3 The total molar amount is 0.7, BaTiO 3 Molar amount accounts for Bi 1.04 FeO 3 、BaTiO 3 When the total molar weight is 0.3, the prepared ceramics have MPB, the highest relative density, the best grain size, and the best comprehensive electrical properties.

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

[0012] (1) Weigh Bi(NO) according to the element molar ratio of Bi:Fe=1.04:1 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O, change Bi(NO 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O is dissolved in an organic solvent, and then an additive is added to the solution, and the solution is stirred, aged, dried, ground, and pre-calcined to obtain Bi 1.04 FeO 3 Powder;

[0013] (2) Weigh C according to the element molar ratio of Ba:Ti=1:1 4 H 8 BaO 4 , C 16 H 36 O 4 Ti, C 4 H 8 BaO 4 , C 16 H 36 O 4 Ti is dissolved in an organic solvent, and the solution is then stirred, aged, dried, ground, and pre-calcined to obtain BaTiO 3 Powder;

[0014] (3) Weigh Bi(NO) according to the element molar ratio of Bi:Na:Ti=0.5:0.5:1 3 ) 3 ·5H 2O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti, Bi(NO 3 ) 3 ·5H 2 O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti is dissolved in an organic solvent, and then the solution is stirred, aged, dried, ground, and pre-calcined in sequence to obtain (Bi 0.5 Na 0.5 )TiO 3 Powder;

[0015] (4) Using the Bi prepared in step (1) 1.04 FeO 3 powder, BaTiO prepared in step (2) 3 Powder, (Bi prepared in step (3) 0.5 Na 0.5 )TiO 3 The powder is used as the raw material, the raw material is weighed according to the stoichiometric ratio, and the raw material is 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 sequentially granulated, molded, debinded, sintered, and then cooled in a furnace to obtain a ceramic sheet, and then the ceramic sheet is silver-plated and polarized to obtain a lead-free piezoelectric ceramic material.

[0017] Preferably, the organic solvent in step (1) is C 3 H 8 O 2 , C 2 H 4 O 2 A mixed liquid, where C 3 H 8 O 2 , C 2 H 4 O 2 The volume ratio is C 3 H 8 O 2 :C 2 H 4 O 2 =3:1, additives include dispersant (CH 2 OH) 2, Stabilizer C 2 H 7 NO, chelating agent C 6 H 8 O 7 ·H 2 O, said (CH 2 OH) 2 The molar ratio of the added amount to the molar amount of metal cations in the solution is (CH 2 OH) 2 :metal cation=1:1,the C 2 H 7 The molar ratio of NO added to the molar amount of metal cations in the solution is C 2 H 7 NO: metal cation = 1:1, the C 6 H 8 O 7 ·H 2 The molar ratio of O added to the molar amount of metal cations in the solution is C 6 H 8 O 7 ·H 2 O: metal cation = 1.15:1;

[0018] The organic solvent in step (2) is C 2 H 4 O 2 , C 2 H 5 OH mixed liquid, where C 2 H 4 O 2 , C 2 H 5 The volume ratio of OH is C 2 H 4 O 2 :C 2 H 5 OH = 4:1;

[0019] The organic solvent in step (3) is (CH 2 OH) 2 , C 2 H 4 O 2 A mixed liquid, where (CH 2 OH) 2 , C 2 H 4 O 2 The volume ratio is (CH 2 OH) 2 :C 2 H 4 O 2 =4:1.

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

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

[0022] In the step (3), the mixed body fluid is stirred at 60° C. for 2 to 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 the 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 specific process of the pre-calcination treatment is: heating the ground material to 550°C at a heating rate of 5±0.5°C / min and keeping the temperature for 4 hours;

[0026] In the step (2), the specific process of the pre-sintering treatment is: heating the ground material to 1000° C. at a heating rate of 5±0.5° C. / min and keeping the temperature for 2 hours;

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

[0028] Preferably, the two ball milling media in step (4) 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 specific pre-calcination process is: the material after the first drying is heated to 800 ° C at a heating rate of 5 ± 0.5 ° C / min, and kept warm for 2 h.

[0029] Preferably, in step (5), the binder used for granulation is a polyvinyl alcohol aqueous solution with a mass concentration of 5%, and the specific molding process is: the granulated product is pressed into a ceramic body at a pressure of 2 to 10 MPa.

[0030] Preferably, the specific process of debinding in step (5) is as follows: the formed ceramic body is heated to 600°C at a heating rate of 5±0.5°C / min and then kept warm for 3h. The sintering is carried out in two steps. First, the debinding material is sintered at 1025°C for 30min, then the temperature is reduced to 900°C and sintered for 90min.

[0031] Preferably, in step (5), the specific polarization process is: sandwich the ceramic sheet between the positive and negative electrodes and immerse them in silicone oil at 120±5°C, then energize the positive and negative electrodes and maintain the voltage at 40-50 kV / cm, and the polarization time is 30±1 min.

[0032] Beneficial effects of the present invention:

[0033] 1. The residual polarization intensity P of the piezoelectric ceramic material prepared by the present invention r Can reach 33.39μC / cm 2 , the leakage current density J can reach 1.94×10 -5 A / cm 2 , inverse piezoelectric constant It can reach 173.9pm / V.

[0034] 2. The present invention prepares Bi by adding excess Bi element 1.04 FeO 3 The powder can compensate for the volatilization of Bi element in the preparation process, thereby reducing the influence of Bi element volatilization on the performance of ceramic materials.

[0035] 3. The preparation method of the present invention has good controllability and 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 the present 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 the present invention has excellent substitution potential for PZT-based ceramics, and can effectively avoid environmental pollution and health hazards caused by lead oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The SEM images of the piezoelectric ceramic materials prepared in Example 1 and Comparative Examples 1-5 of the present invention are shown in FIG. (a) is a SEM image of the piezoelectric ceramic material of Example 1, FIG. (b) is a SEM image of the piezoelectric ceramic material of Comparative Example 1, FIG. (c) is a SEM image of the piezoelectric ceramic material of Comparative Example 2, FIG. (d) is a SEM image of the piezoelectric ceramic material of Comparative Example 3, FIG. (e) is a SEM image of the piezoelectric ceramic material of Comparative Example 4, and FIG. (f) is a SEM image of the piezoelectric ceramic material of Comparative Example 5;

[0039] Figure 2 These are XPS measurement spectra of the piezoelectric ceramic materials prepared in Example 1 and Comparative Examples 1-5 of the present invention, wherein Figure (a) is an XPS measurement spectrum of Fe 2p nuclear energy level, and Figure (b) is an XPS measurement spectrum of O1s nuclear energy level. DETAILED DESCRIPTION

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

[0041] In the examples and comparative examples of the present invention, chemical reagents not specifically described were commercially available analytically pure reagents for the experiments.

[0042] Example 1

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

[0044] (1) Weigh Bi(NO) according to the element molar ratio of Bi:Fe=1.04:1 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O. Bi(NO 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O is dissolved in C 3 H 8 O 2 :C 2 H 4 O 2 =3:1 mixed liquid, stirring Bi(NO 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O dissolves, and after it dissolves, add (CH 2 OH) 2 , C 2 H 7 NO, C 6 H 8 O 7 ·H 2 O, and the solution was stirred at room temperature for 24 hours, then aged for 48 hours in a dark environment, and then dried at 85°C. After drying for 48 hours, a solid substance was obtained, which was ground into powder, and then the powder was heated to 550°C at a heating rate of 5±0.5°C / min and kept warm for 4 hours to remove volatile impurities, thereby obtaining Bi 1.04 FeO 3 powder.

[0045] (2) Weigh C according to the element molar ratio of Ba:Ti=1:1 4 H 8 BaO 4 , C 16 H 36 O 4 Ti. C 4 H 8 BaO 4 , C 16 H 36 O 4 Ti is dissolved in C 4 H 8 BaO 4 :C 16 H 36 O 4 The solution was stirred at 60°C for 5 hours in a mixed liquid of Ti=4:1, then aged for 48 hours under light-proof conditions, and then dried at 85°C for 48 hours to obtain a solid substance, which was ground into powder, and then heated to 1000°C at a heating rate of 5±0.5°C / min and kept warm for 2 hours to remove volatile impurities, thereby obtaining BaTiO 3 powder.

[0046] (3) Weigh Bi(NO) according to the element molar ratio of Bi:Na:Ti=0.5:0.5:1 3 ) 3 ·5H 2 O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti. Bi(NO 3 ) 3 ·5H 2 O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti is dissolved in a volume ratio of (CH 2 OH) 2 :

[0047] C 2 H 4 O 2=4:1 mixed liquid, the solution was stirred at 60°C for 2.5h, then aged for 72h under light-proof conditions, and then dried at 85°C for 7 days to obtain a solid substance, which was ground into powder, and then the powder was heated to 650°C at a heating rate of 5±0.5°C / min and kept warm for 2h to remove volatile impurities, to obtain (Bi 0.5 Na 0.5 )TiO 3 powder.

[0048] (4) Use Bi 1.04 FeO 3 Powder, BaTiO 3 Powder, (Bi 0.5 Na 0.5 )TiO 3 Powder as raw material, according to the chemical expression 0.96 (0.7Bi 1.04 FeO 3 -0.3BaTiO 3 )-0.04(Bi 0.5 Na 0.5 )TiO 3 Weigh the powder raw materials in a stoichiometric ratio. Use anhydrous ethanol as the ball milling medium, select agate balls as ball milling beads, mix them in a mass ratio of raw materials: agate balls: ethanol = 1:2.2:2.4, planetary ball mill at a speed of 160rpm for 24h, and dry after ball milling. Heat the dry material to 800℃ at a heating rate of 5±0.5℃ / min and keep it warm for 2h to pre-calcine to improve the uniformity of the powder and react it to obtain the main crystalline phase. The pre-calcined powder is ball milled again under the same ball milling conditions as the above ball milling conditions. Dry after ball milling to obtain a mixed powder.

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

[0050] The piezoelectric ceramic material prepared in this example was tested by SEM, and the results are as follows: Figure 1 shown.

[0051] The piezoelectric ceramic material prepared in this example was subjected to XPS testing, and the results are as follows: Figure 2 shown.

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

[0053] Example 2

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

[0055] (1) Weigh Bi(NO) according to the element molar ratio of Bi:Fe=1.04:1 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O. Bi(NO 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O is dissolved in C 3 H 8 O 2 :C 2 H4 O 2 =3:1 mixed liquid, stirring Bi(NO 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O dissolves, and after it dissolves, add (CH 2 OH) 2 , C 2 H 7 NO, C 6 H 8 O 7 ·H 2 O, and the solution was stirred at room temperature for 24 hours, then aged for 48 hours in a dark environment, and then dried at 85°C. After drying for 48 hours, a solid substance was obtained, which was ground into powder, and then the powder was heated to 550°C at a heating rate of 5±0.5°C / min and kept warm for 4 hours to remove volatile impurities, thereby obtaining Bi 1.04 FeO 3 powder.

[0056] (2) Weigh C according to the element molar ratio of Ba:Ti=1:1 4 H 8 BaO 4 , C 16 H 36 O 4 Ti. C 4 H 8 BaO 4 , C 16 H 36 O 4 Ti is dissolved in C 4 H 8 BaO 4 :C 16 H 36 O 4 The solution was stirred at 60°C for 4 hours in a mixed liquid of Ti=4:1, then aged for 48 hours under light-proof conditions, and then dried at 85°C for 48 hours to obtain a solid substance, which was ground into powder, and then heated to 1000°C at a heating rate of 5±0.5°C / min and kept warm for 2 hours to remove volatile impurities, thereby obtaining BaTiO 3 powder.

[0057] (3) Weigh Bi(NO) according to the element molar ratio of Bi:Na:Ti=0.5:0.5:1 3 ) 3 ·5H 2O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti. Bi(NO 3 ) 3 ·5H 2 O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti is dissolved in a volume ratio of (CH 2 OH) 2 :

[0058] C 2 H 4 O 2 =4:1 mixed liquid, the solution was stirred at 60°C for 2h, then aged for 72h under light-proof conditions, and then dried at 85°C for 7 days to obtain a solid substance, the solid substance was ground into powder, and then the powder was heated to 650°C at a heating rate of 5±0.5°C / min and kept warm for 2h to remove volatile impurities, to obtain (Bi 0.5 Na 0.5 )TiO 3 powder.

[0059] (4) Use Bi 1.04 FeO 3 Powder, BaTiO 3 Powder, (Bi 0.5 Na 0.5 )TiO 3 Powder as raw material, according to the chemical expression 0.96 (0.7Bi 1.04 FeO 3 -0.3BaTiO 3 )-0.04(Bi 0.5 Na 0.5 )TiO 3 Weigh the powder raw materials in a stoichiometric ratio. Use anhydrous ethanol as the ball milling medium, select agate balls as ball milling beads, mix them in a mass ratio of raw materials: agate balls: ethanol = 1:2.2:2.4, planetary ball mill at a speed of 160rpm for 24h, and dry after ball milling. Heat the dry material to 800℃ at a heating rate of 5±0.5℃ / min and keep it warm for 2h to pre-calcine to improve the uniformity of the powder and react it to obtain the main crystalline phase. The pre-calcined powder is ball milled again under the same ball milling conditions as the above ball milling conditions. Dry after ball milling to obtain a mixed powder.

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

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

[0062] Example 3

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

[0064] (1) Weigh Bi(NO) according to the element molar ratio of Bi:Fe=1.04:1 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O. Bi(NO 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2 O is dissolved in C 3 H 8 O 2 :C 2 H 4 O 2 =3:1 mixed liquid, stirring Bi(NO 3 ) 3 ·5H 2 O, Fe(NO 3 ) 3 9H 2O dissolves, and after it dissolves, add (CH 2 OH) 2 , C 2 H 7 NO, C 6 H 8 O 7 ·H 2 O, and the solution was stirred at room temperature for 24 hours, then aged for 48 hours in a dark environment, and then dried at 85°C. After drying for 48 hours, a solid substance was obtained, which was ground into powder, and then the powder was heated to 550°C at a heating rate of 5±0.5°C / min and kept warm for 4 hours to remove volatile impurities, thereby obtaining Bi 1.04 FeO 3 powder.

[0065] (2) Weigh C according to the element molar ratio of Ba:Ti=1:1 4 H 8 BaO 4 , C 16 H 36 O 4 Ti. C 4 H 8 BaO 4 , C 16 H 36 O 4 Ti is dissolved in C 4 H 8 BaO 4 :C 16 H 36 O 4 The solution was stirred at 60°C for 6 hours in a mixed liquid of Ti=4:1, then aged for 48 hours under light-proof conditions, and then dried at 85°C for 48 hours to obtain a solid substance, which was ground into powder, and then heated to 1000°C at a heating rate of 5±0.5°C / min and kept warm for 2 hours to remove volatile impurities, thereby obtaining BaTiO 3 powder.

[0066] (3) Weigh Bi(NO) according to the element molar ratio of Bi:Na:Ti=0.5:0.5:1 3 ) 3 ·5H 2 O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti. Bi(NO 3 ) 3 ·5H 2O.C 2 H 3 NaO 2 , C 16 H 36 O 4 Ti is dissolved in a volume ratio of (CH 2 OH) 2 :

[0067] C 2 H 4 O 2 =4:1 mixed liquid, the solution was stirred at 60°C for 3h, then aged for 72h under light-proof conditions, and then dried at 85°C for 7 days to obtain a solid substance, which was ground into powder, and then the powder was heated to 650°C at a heating rate of 5±0.5°C / min and kept warm for 2h to remove volatile impurities, to obtain (Bi 0.5 Na 0.5 )TiO 3 powder.

[0068] (4) Use Bi 1.04 FeO 3 Powder, BaTiO 3 Powder, (Bi 0.5 Na 0.5 )TiO 3 Powder as raw material, according to the chemical expression 0.96 (0.7Bi 1.04 FeO 3 -0.3BaTiO 3 )-0.04(Bi 0.5 Na 0.5 )TiO 3 Weigh the powder raw materials in a stoichiometric ratio. Use anhydrous ethanol as the ball milling medium, select agate balls as ball milling beads, mix them in a mass ratio of raw materials: agate balls: ethanol = 1:2.2:2.4, planetary ball mill at a speed of 160rpm for 24h, and dry after ball milling. Heat the dry material to 800℃ at a heating rate of 5±0.5℃ / min and keep it warm for 2h to pre-calcine to improve the uniformity of the powder and react it to obtain the main crystalline phase. The pre-calcined powder is ball milled again under the same ball milling conditions as the above ball milling conditions. Dry after ball milling to obtain a mixed powder.

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

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

[0071] Comparative Example 1

[0072] This comparative example adopts the same method as that of Example 1 to prepare a lead-free piezoelectric ceramic material, 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 shown.

[0074] The piezoelectric ceramic material prepared in this comparative example was subjected to XPS testing, and the results are as follows: Figure 2 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 adopts the same method as that of Example 1 to prepare a lead-free piezoelectric ceramic material, 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 shown.

[0079] The piezoelectric ceramic material prepared in this comparative example was subjected to XPS testing, and the results are as follows: Figure 2 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 adopts the same method as that of Example 1 to prepare a lead-free piezoelectric ceramic material, 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 shown.

[0084] The piezoelectric ceramic material prepared in this comparative example was subjected to XPS testing, and the results are as follows: Figure 2 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 adopts the same method as that of Example 1 to prepare a lead-free piezoelectric ceramic material, 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 shown.

[0089] The piezoelectric ceramic material prepared in this comparative example was subjected to XPS testing, and the results are as follows: Figure 2 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 adopts the same method as that of Example 1 to prepare a lead-free piezoelectric ceramic material, 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 shown.

[0094] The piezoelectric ceramic material prepared in this comparative example was subjected to XPS testing, and the results are as follows: Figure 2 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] It can be seen from Table 1 that compared with Comparative Examples 1-5, Example 1 has the highest residual polarization intensity, the lowest leakage current density, the highest inverse piezoelectric constant, and the highest relative density, indicating that Example 1 has the best piezoelectric performance relative to Comparative Examples 1-5, and the high residual polarization intensity and low leakage current density indicate that the piezoelectric ceramic material of Example 1 has excellent ferroelectric performance in addition to excellent piezoelectric performance. Compared with Comparative Examples 2-4, although the increase in the residual polarization intensity of Example 1 and the decrease in the leakage current density are limited, the inverse piezoelectric constant of Example 1 is significantly improved, and compared with Comparative Example 1, the increase in the inverse piezoelectric constant of Example 1 is limited, but its residual polarization intensity and leakage current density are significantly improved. It can be seen that the value of x has a significant impact on the comprehensive electrical properties (piezoelectric properties, ferroelectric properties) of the piezoelectric ceramic material, and only when x=0.04, the comprehensive electrical properties of the piezoelectric ceramic material are the best, and after changing the value of x, the comprehensive performance of the piezoelectric ceramic material is significantly reduced.

[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 still have some pores. The generation of pores may be caused by the volatilization of Bi ions, which fully demonstrates that Bi ions will volatilize during the preparation process. Therefore, Bi ions need to be compensated to reduce the generation of pores and improve the density of the microstructure of piezoelectric ceramic materials. Figure 1 It 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 is significantly reduced. This may be due to the relatively low mole fraction of BNT doping, which can effectively pin the grain boundaries and limit grain growth. As the BNT content increases, the comprehensive electrical properties of the piezoelectric ceramic material are improved to a certain extent. However, compared with Comparative Example 1, the inverse piezoelectric constant of Comparative Example 2 is greatly reduced, indicating that for piezoelectric ceramic materials, the average grain size needs to be maintained at an appropriate level. Too fine or too coarse will have a greater negative impact on the comprehensive electrical properties of the piezoelectric ceramic material. As the BNT doping amount further increases, the average grain size refinement slows down, which may be due to the fact that the effect of the doped third component is close to saturation or the grain boundary migration resistance reaches a limit. As a result, the beneficial effect of the average grain size refinement is weakened, while the negative impact caused by too fine grains is aggravated, showing a more obvious negative impact on the comprehensive electrical properties 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 of Fe 3+ / Fe 2+The peak area ratios are 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 the present invention effectively suppresses the 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, which fully proves 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 comprehensive electrical properties of the piezoelectric ceramic material.

[0101] In summary, the piezoelectric ceramic material of the present invention can effectively reduce the negative impact of Bi volatilization on performance, while improving the material microstructure and inhibiting Fe 3+ Converted to Fe 2+ , and inhibit the formation of oxygen vacancies, reduce the concentration of oxygen vacancies, and ultimately make the piezoelectric ceramic material have 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 rather than 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 in form and details 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 expression of 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 comprises the following steps: (1) Bi(NO3)3·5H2O and Fe(NO3)3·9H2O are weighed according to the element molar ratio of Bi:Fe=1.04:1, Bi(NO3)3·5H2O and Fe(NO3)3·9H2O are dissolved in an organic solvent, and then an additive is added to the solution, and the solution is stirred, aged, dried, ground, and pre-calcined to obtain Bi 1.04 FeO3 powder; (2) Weigh C4H8BaO4, C4H8BaO4 and C4H8BaO4 according to the 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 16 H 36 O4Ti, Bi(NO3)3·5H2O, C2H3NaO2, 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 (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), (Bi 0.5 Na 0.5 ) TiO3 powder is used as a raw material, the raw material is weighed according to the stoichiometric ratio, and the raw material is subjected to ball milling, drying, pre-calcining, secondary ball milling, and secondary drying in sequence to obtain a uniformly mixed mixed powder; (5) The mixed powder obtained in step (4) is sequentially granulated, molded, debinded, sintered, and then cooled in a furnace to obtain a ceramic sheet, and then the ceramic sheet is silver-plated and polarized to obtain a lead-free piezoelectric ceramic material.

3. The preparation method according to claim 2, characterized in that: In the 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 a dispersant (CH2OH)2, a stabilizer C2H7NO, and a 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; 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; The organic solvent in step (3) is a mixed liquid of (CH2OH)2 and C2H4O2, wherein the volume ratio of (CH2OH)2 and C2H4O2 is (CH2OH)2:C2H4O2=4:

1.

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

5. The preparation method according to claim 2, characterized in that: In the steps (1) and (2), the aging time is 48 hours, the drying temperature is 85° C., and the drying time is 48 hours; In the 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 the step (1), the specific process of the pre-calcination treatment is: heating the ground material to 550° C. at a heating rate of 5±0.5° C. / min and keeping the temperature for 4 hours; In the step (2), the specific process of the pre-sintering treatment is: heating the ground material to 1000° C. at a heating rate of 5±0.5° C. / min and keeping the temperature for 2 hours; In the step (3), the specific process of the pre-sintering treatment is: heating the ground material to 650° C. at a heating rate of 5±0.5° C. / min and keeping the temperature for 2 hours.

7. The preparation method according to claim 2, characterized in that: In the step (4), the ball milling medium for both times is 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 specific pre-calcination process is: the material after the first drying is heated to 800 ° C at a heating rate of 5 ± 0.5 ° C / min, and kept warm for 2 h.

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

9. The preparation method according to claim 2, characterized in that: The specific process of debinding in step (5) is as follows: the formed ceramic body is heated to 600°C at a heating rate of 5±0.5°C / min and then kept warm for 3 hours. The sintering is carried out in a two-step manner. First, the debinding material is sintered at 1025°C for 30 minutes, then the temperature is reduced to 900°C and sintered for another 90 minutes.

10. The preparation method according to claim 2, characterized in that: In step (5), the specific polarization process is: sandwich the ceramic sheet between the positive and negative electrodes and immerse them in silicone oil at 120±5°C, then energize the positive and negative electrodes and maintain the voltage at 40-50 kV / cm, and the polarization time is 30±1 min.

Images