A bismuth ferrite-barium titanate ceramic with piezoelectric coefficient temperature stability and a preparation method thereof

Abstract

The application discloses a bismuth ferrite-barium titanate ceramic with temperature stability of piezoelectric coefficient and a preparation method thereof. 1‑ x Ce x TiO3+ywt.%MnO2, wherein 0<=x<=0.05, 0<y<=0.5. The bismuth ferrite-barium titanate ceramic provided by the application selects Ce 4+ performs "donor" doping, replaces Ba 2+ and introduces excess free positive charges (holes), and the positive charges can compensate for Fe 3+ reduced into Fe 2+ formed positive oxygen vacancies, thereby inhibiting the generation of oxygen vacancies, and in combination with rapid quenching, the piezoelectric coefficient of the bismuth ferrite-barium titanate ceramic is kept stable within a certain temperature range, and the temperature stability of the piezoelectric performance is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lead-free ferroelectric ceramics, and particularly relates to a bismuth ferrite-barium titanate ceramic with temperature stability of a piezoelectric coefficient and a preparation method thereof. BACKGROUND

[0002] The bismuth ferrite-barium titanate ceramic (BiFeO3-BaTiO3, referred to as BF-BT) is a lead-free piezoelectric ceramic material with a perovskite structure. It is considered as a potential new type of lead-free piezoelectric ceramic material due to its good piezoelectric performance and high Curie temperature. The research and application of this material have attracted widespread attention in recent years, especially in high-temperature environments such as aerospace, geological exploration, petrochemical industry, automobile engine, etc.

[0003] Since one of the main matrices of the bismuth ferrite-barium titanate ceramic is bismuth ferrite, this type of ceramic has some problems of bismuth ferrite ceramic sintering, such as being a metastable structure in the range of 447-767℃, easily decomposing into Bi-rich and Fe-rich impurities, resulting in the existence of secondary phases in the ceramic, making it difficult to obtain pure phases. At the same time, the bismuth ferrite-barium titanate ceramic also has problems such as Bi element volatilization at high temperature, Fe 3+ valence change, and a large number of oxygen vacancies and other point defects exist in the ceramic. These oxygen vacancies will induce the transformation of rhombohedral phase in bismuth ferrite-barium titanate from R3c to R3m phase structure at high temperature, the degree of oxygen octahedral distortion decreases, the restriction on ferroelectric domains weakens, and the piezoelectric coefficient increases. Therefore, the existence of these defects is not conducive to the stability of the composition and structure of BF-BT solid solution at high temperature, greatly limiting its practical application in high-temperature environments.

[0004] Patent (CN115073159B) discloses a bismuth ferrite-barium titanate ceramic with high Curie temperature and high piezoelectric performance and a low-temperature oxygen-containing hot-pressing sintering preparation method. The bismuth ferrite-barium titanate ceramic prepared by low-temperature oxygen-containing hot-pressing sintering has a piezoelectric coefficient d 33 of 498pC / N at the highest temperature point of 315℃.

[0005] Patent (CN115073160B) discloses a hot-pressing sintering preparation method of a bismuth ferrite-barium titanate ceramic with a micro-nano electric domain structure. The bismuth ferrite-barium titanate ceramic prepared by using sintering aids and hot-pressing repeated "hammering" process has a piezoelectric coefficient d 33 of 502pC / N at the highest temperature point of 360℃.

[0006] Patent (CN115093212B) discloses a high-performance bismuth ferrite-barium titanate ceramic with an operating temperature exceeding 300℃ and its low-temperature liquid-phase sintering preparation method. The bismuth ferrite-barium titanate ceramic prepared by this method exhibits a piezoelectric coefficient d at a maximum temperature of 360℃. 33 More than 400pC / N.

[0007] However, the piezoelectric coefficient (d) of bismuth ferrite-barium titanate ceramics 33 At high temperatures, they are all lower than at room temperature. 33 While improving performance by 2-3 times, it exhibits relatively poor temperature stability, which is detrimental to maintaining stable signal output for high-temperature piezoelectric sensors within their operating temperature range. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the first objective of this invention is to provide a bismuth ferrite-barium titanate ceramic with temperature stability of piezoelectric coefficient. The piezoelectric coefficient of the bismuth ferrite-barium titanate ceramic provided by this invention remains stable within a certain temperature range, and its piezoelectric properties exhibit excellent temperature stability.

[0009] The second objective of this invention is to provide a method for preparing bismuth ferrite-barium titanate ceramics with piezoelectric coefficient temperature stability. The preparation process of this invention is simple and controllable.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] This invention discloses a bismuth ferrite-barium titanate ceramic with piezoelectric coefficient temperature stability, wherein the chemical formula of the bismuth ferrite-barium titanate ceramic is: 0.75BiFeO3-0.25Ba 1-x Ce x TiO3+y wt.%MnO2, where 0≤x≤0.05, 0 <y≤0.5。

[0012] The bismuth ferrite-barium titanate ceramic provided by this invention uses Ce with a higher ionic valence state. 4+ "Donor" doping was performed, replacing Ba. 2+ Then, excess free positive charges (holes) will be introduced, which can compensate for the Fe at high temperatures. 3+ Reduced to Fe 2+ The positively charged oxygen vacancies formed suppress the generation of oxygen vacancies. The defect reaction equation is as follows:

[0013]

[0014] The reduction in oxygen vacancy content significantly reduces the dielectric loss and increases the resistivity of bismuth ferrite-barium titanate ceramics, thereby improving the polarization efficiency of the ceramics and thus enhancing their piezoelectric properties.

[0015] Preferably, the bismuth ferrite-barium titanate ceramic has a chemical formula of: 0.75BiFeO3-0.25Ba 1-x Ce x TiO3+y wt.%MnO2, wherein 0.005≤x≤0.05, 0.10≤y≤0.15.

[0016] Further preferably, the bismuth ferrite-barium titanate ceramic has a chemical formula of: 0.75BiFeO3-0.25Ba 1- x Ce x TiO3+y wt.%MnO2, wherein 0.01≤x≤0.05, 0.10≤y≤0.15.

[0017] Still further preferably, the bismuth ferrite-barium titanate ceramic has a chemical formula of: 0.75BiFeO3-0.25Ba 1- x Ce x TiO3+y wt.%MnO2, wherein 0.01≤x≤0.02, 0.10≤y≤0.15.

[0018] The application provides a preparation method of a bismuth ferrite-barium titanate ceramic with temperature stability of piezoelectric coefficient, which comprises the following steps: mixing oxide raw materials according to the chemical formula of the bismuth ferrite-barium titanate ceramic to obtain a mixed powder, pre-sintering the mixed powder to obtain pre-sintered powder, granulating the pre-sintered powder to obtain granules, pressing the granules to obtain a green body, and quenching the green body in cooling water after glue removal and sintering.

[0019] The preparation method provided by the application can greatly shorten the migration time of oxygen atoms during the quenching and cooling process, a large number of oxygen atoms are "frozen" in the sites with high symmetry, and the degree of oxygen octahedron distortion in the rhombohedral cell is significantly reduced. This can inhibit the phase structure transition of the bismuth ferrite-barium titanate ceramic during the heating process, that is, the degree of transition from R3c to R3m phase structure is reduced, so that the piezoelectric coefficient at high temperature is reduced, and the oxygen vacancies and other defects in the ceramic are reduced, so that the insulation resistance of the material is improved, and the depolarization starting temperature of the material is prolonged.

[0020] Preferably, the bismuth ferrite-barium titanate ceramic has a chemical formula of: 0.75BiFeO3-0.25Ba 1-x Ce x TiO3+y wt.%MnO2, wherein 0.005≤x≤0.05, 0.10≤y≤0.15.

[0021] Preferably, the mixing method is wet ball milling, the ball milling medium is anhydrous ethanol, and the ball milling time is 4-8 hours.

[0022] In actual operation, the mixture obtained after wet ball milling is dried in an oven at 70℃ for 12 hours, and then sieved through a 40-mesh sieve to obtain a mixed powder.

[0023] Preferably, the pre-sintering temperature is 750-820℃, the pre-sintering time is 3-6 hours, and the temperature increasing rate is 5-15℃ / min. In actual operation, the mixed powder is then placed in an alumina crucible, compacted, covered, and then placed in a muffle furnace for pre-sintering to synthesize the main crystal phase. After cooling to room temperature in the furnace, the product is removed and ready for use.

[0024] Preferably, the pre-sintered powder is ground and sieved through a 100-200 mesh sieve, PVB is added as a binder, and the mixture is stirred and granulated in anhydrous ethanol medium to obtain granules, wherein the mass fraction of PVB in the granules is 1%-5%.

[0025] Preferably, the pressure for pressing is 100-200 MPa.

[0026] Preferably, the temperature for degumming is 400-600℃, the degumming time is 2-8 hours, and the temperature increasing rate is 1-5℃ / min. Through degumming, the PVB binder is removed, and after degumming is completed, the product is cooled to room temperature in the furnace.

[0027] Preferably, the sintering is performed in an oxygen atmosphere, and the sintering process is as follows: increasing the temperature to 980-1020℃ at a temperature increasing rate of 5-15℃ / min, holding for 3-6 hours, and immediately removing the product from the furnace and quenching in cooling water after the holding is completed.

[0028] Further preferably, the temperature of the cooling water is room temperature.

[0029] Advantages

[0030] The bismuth ferrite-barium titanate ceramic provided by the present application selects Ce 4+ "donor" doping, replacing Ba 2+ will introduce excess free positive charges (holes), which can compensate for the loss of Fe 3+ reduced to Fe 2+The formed positive oxygen vacancies, thereby inhibiting the generation of oxygen vacancies. The reduction of oxygen vacancy content greatly reduces the dielectric loss of the bismuth ferrite-barium titanate ceramic, increases the resistivity, thereby leading to the improvement of the polarization efficiency of the ceramic, and thus the piezoelectric performance is improved. In combination with quenching of the sintered blank, the migration time of oxygen atoms is greatly shortened during the quenching cooling process, and a large number of oxygen atoms are 'frozen' in the sites with higher symmetry, and the degree of oxygen octahedron distortion in the rhombohedral unit cell is significantly reduced. This will lead to the inhibition of the phase structure transition of the bismuth ferrite-barium titanate ceramic during heating, i.e. the degree of transition from R3c to R3m phase structure is reduced, thereby reducing the increase range of the piezoelectric coefficient at high temperature 。

[0031] The present application adopts the means of rapid quenching and ion doping in combination to make the piezoelectric coefficient of the bismuth ferrite-barium titanate ceramic stable within a certain temperature range, and improve the temperature stability of the piezoelectric performance.

[0032] The present application breaks through the limitation that the piezoelectric performance of the existing bismuth ferrite-barium titanate ceramic fluctuates greatly with temperature, reduces the fluctuation of the piezoelectric coefficient with temperature while ensuring that the ceramic has excellent piezoelectric performance and high Curie temperature, improves the temperature stability of the piezoelectric coefficient, and does not occur depolarization below the Curie temperature, which provides a new choice for piezoelectric ceramic materials for high-temperature piezoelectric sensors with stable signal output. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The (a) in-situ d of the bismuth ferrite-barium titanate ceramic obtained in Example 1 33 Test results; (b) non-in-situ d 33 Test results.

[0034] Figure 2 The (a) in-situ d of the bismuth ferrite-barium titanate ceramic obtained in Example 2 33 Test results; (b) non-in-situ d 33 Test results.

[0035] Figure 3 The (a) in-situ d of the bismuth ferrite-barium titanate ceramic obtained in Example 3 33 Test results; (b) non-in-situ d 33 Test results.

[0036] Figure 4 The in-situ d of the bismuth ferrite-barium titanate ceramic obtained in Comparative Example 1 33 Test results.

[0037] Figure 5 The in-situ d of the bismuth ferrite-barium titanate ceramic obtained in Comparative Example 2 33 Test results. DETAILED DESCRIPTION

[0038] Example 1

[0039] According to the general chemical formula 0.75BiFeO3-0.25Ba 1-x Ce x TiO3+y wt.%MnO2 is used for batching, where x=0.01 and y=0.15;

[0040] After ball milling the mixed powder with anhydrous ethanol for 6 hours, it was taken out and placed in an oven to dry at 70°C for 12 hours. It was then passed through a 40-mesh sieve, compacted and covered in an alumina crucible, and then placed in a muffle furnace and heated to 800°C at a heating rate of 10°C / min for pre-calcination. The temperature was held for 4 hours to synthesize the main crystalline phase. After cooling to room temperature with the furnace, it was taken out for use.

[0041] The pre-calcined powder was thoroughly ground and passed through a 100-mesh sieve. 3% PVB powder was added as a binder and stirred and granulated with anhydrous ethanol as the medium. The powder was then dry-pressed in a powder tablet press at a pressure of 200 MPa to obtain a round green sheet with a diameter × height of 10 mm × 1 mm.

[0042] The formed round green blanks are placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min for debinding. The blanks are held at this temperature for 2 hours to remove the PVB binder and then cooled to room temperature in the furnace. Oxygen is then introduced and the blanks are heated to 1000°C at a heating rate of 10°C / min for sintering. The blanks are held at this temperature for 4 hours. After the holding period, the blanks are immediately removed from the furnace and placed in cold water for quenching.

[0043] The surface of the sintered circular sample was polished into a flat sheet with a thickness of 0.6 mm. Silver electrodes were plated onto the polished ceramic sheet, and the sheet was fired at 850℃ for 15 min before being immediately removed from the furnace. The silver-fired ceramic sheet was then polarized in silicone oil with a polarization electric field of 60 kV / cm, perpendicular to the radial direction of the disc, a polarization temperature of 120℃, a polarization time of 30 min, and a voltage ramp rate of 2 V / s. After removal, the sheet was allowed to stand at room temperature and in air for 48 h.

[0044] d of the sample at room temperature 33 It is 110.2 pC / N, k p =0.37, Q m =159, ε r =425, tanδ=0.01, T C =577℃. In-situ d 33 Test results show that the maximum d of the sample at 300℃ 33 It is 142.6 pC / N, compared to room temperature d 33 The value increased by approximately 29.4%. The depolarization onset temperature is 300℃. Non-in-situ d 33Test results show that within the temperature range of 25-575℃, d 33 The decline rate is no more than 5%. See Figure 1 .

[0045] Example 2

[0046] According to the general chemical formula 0.75BiFeO3-0.25Ba 1-x Ce x TiO3 + y wt.% MnO2 were mixed, where x = 0 and y = 0.15. The mixed powder was ball-milled for 6 hours with anhydrous ethanol as the medium, then dried in an oven at 70°C for 12 hours, passed through a 40-mesh sieve, compacted and covered in an alumina crucible, and then pre-calcined in a muffle furnace at a heating rate of 10°C / min to 800°C for 4 hours to synthesize the main crystalline phase. After cooling to room temperature in the furnace, the powder was removed for later use. The pre-calcined powder was thoroughly ground, passed through a 100-mesh sieve, and 3% PVB powder was added as a binder. The mixture was stirred and granulated with anhydrous ethanol as the medium. The granulated powder was then dry-pressed in a powder press at a pressure of 200 MPa to obtain a circular green compact with a diameter × height of 10 mm × 1 mm. The formed circular preforms were placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min for debinding. The temperature was held for 2 hours to remove the PVB binder, and then cooled to room temperature in the furnace. Oxygen was then introduced, and the temperature was increased to 1000°C at a heating rate of 10°C / min for sintering. The temperature was held for 4 hours, and immediately removed from the furnace after holding. The preforms were then quenched in cold water. The surface of the sintered circular sample was polished into a flat sheet with a thickness of 0.6 mm. Silver electrodes were plated onto the polished ceramic sheet, and the sheet was fired at 850°C for 15 minutes before being immediately removed from the furnace. The silver-fired ceramic sheet was then polarized in silicone oil with a polarization electric field of 60 kV / cm, perpendicular to the radial direction of the disc, a polarization temperature of 120°C, a polarization time of 30 minutes, and a voltage increase rate of 2 V / s. After removal, the sheet was allowed to stand at room temperature and in air for 48 hours.

[0047] d of the sample at room temperature 33 It is 107.7 pC / N, k p =0.36, Q m =161, ε r =437, tanδ=0.016, T C =581℃. In-situ d 33 Test results show that the maximum d of the sample at 263℃ 33 It is 144.8 pC / N, compared to room temperature d 33 The value increased by approximately 37.5%. The depolarization onset temperature was 263℃. Non-in-situ d 33 Test results show that within the temperature range of 25-575℃, d 33 The decline rate is no more than 5%. SeeFigure 2 .

[0048] Example 3

[0049] According to the general chemical formula 0.75BiFeO3-0.25Ba 1-x Ce x TiO3 + y wt.% MnO2 were mixed, where x = 0.05 and y = 0.15. The mixed powder was ball-milled for 6 hours with anhydrous ethanol as the medium, then placed in an oven and dried at 70℃ for 12 hours. After passing through a 40-mesh sieve, it was placed in an alumina crucible, compacted, and covered. Then, it was placed in a muffle furnace and heated to 800℃ at a heating rate of 10℃ / min for pre-calcination, held at that temperature for 4 hours to synthesize the main crystalline phase. After cooling to room temperature with the furnace, it was taken out for use. The pre-calcined powder was thoroughly ground, passed through a 100-mesh sieve, and 3% PVB powder was added as a binder. The mixture was stirred and granulated with anhydrous ethanol as the medium. The powder was then dry-pressed in a powder tablet press at a pressure of 200MPa to obtain a circular green compact with a diameter × height of 10mm × 1mm. The formed circular preforms were placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min for debinding. The temperature was held for 2 hours to remove the PVB binder, and then cooled to room temperature in the furnace. Oxygen was then introduced, and the temperature was increased to 1000°C at a heating rate of 10°C / min for sintering. The temperature was held for 4 hours, and immediately removed from the furnace after holding. The preforms were then quenched in cold water. The surface of the sintered circular sample was polished into a flat sheet with a thickness of 0.6 mm. Silver electrodes were plated onto the polished ceramic sheet, and the sheet was fired at 850°C for 15 minutes before being immediately removed from the furnace. The silver-fired ceramic sheet was then polarized in silicone oil with a polarization electric field of 60 kV / cm, perpendicular to the radial direction of the disc, a polarization temperature of 120°C, a polarization time of 30 minutes, and a voltage increase rate of 2 V / s. After removal, the sheet was allowed to stand at room temperature and in air for 48 hours.

[0050] d of the sample at room temperature 33 It is 73.3 pC / N, k p =0.23, Q m =65, ε r =530, tanδ=0.036, T C =602℃. In-situ d 33 Test results show that the maximum d of the sample at 263℃ 33 It is 149.5 pC / N, compared to room temperature d 33 The value increases by approximately 104%. The depolarization onset temperature is 315℃. (Extra-in-situ d) 33 Test results show that within the temperature range of 25-150℃, d 33 The decline rate is no more than 5%. See Figure 3 .

[0051] Comparative Example 1

[0052] According to the chemical formula 0.75BiFeO3-0.25Ba 1-x Ce x TiO3+y wt. % MnO2, wherein x = 0.01, y = 0.15; the mixed powder is ball-milled in anhydrous ethanol as a medium for 6 h, taken out, dried in an oven at 70 °C for 12 h, passed through a 40-mesh sieve, then put into an alumina crucible, compacted, covered, and heated to 800 °C at a heating rate of 10 °C / min in a muffle furnace for pre-sintering, and kept for 4 h to synthesize the main crystal phase, and taken out after the furnace is cooled to room temperature for standby use. The pre-sintered powder is thoroughly ground, passed through a 100-mesh sieve, 3% PVB powder by mass fraction is added as a binder and stirred for granulation in anhydrous ethanol as a medium, and dry-pressed in a powder tablet machine at a pressure of 200 MPa to obtain green bodies in the form of circular tablets with a diameter x height of 10 mm x 1 mm. The formed circular tablet green bodies are put into a tube furnace, heated to 400 °C at a heating rate of 2 °C / min for degassing, kept for 2 h to remove the PVB binder, and cooled to room temperature in the furnace. Oxygen is passed again to heat to 1000 °C at a heating rate of 10 °C / min for sintering, kept for 4 h, and cooled to room temperature in the furnace. The surface of the sintered circular tablet sample is polished to a thickness of 0.6 mm, and silver electrodes are plated on the polished ceramic tablets, and the ceramic tablets are taken out immediately after silver is burned at 850 °C for 15 min. The silver-burned ceramic tablets are polarized in silicone oil, the polarization electric field is 60 kV / cm, the polarization electric field direction is perpendicular to the diameter direction of the circular tablets, the polarization temperature is 120 °C, the polarization time is 30 min, the voltage rising speed is 2 V / s, and the sample is taken out and left to stand in air at room temperature for 48 h.

[0053] The d 33 at room temperature is 105.3 pC / N, k p = 0.36, Q m = 131, ε r = 450, tan δ = 0.021, and T C = 557 °C. The in-situ d 33 test results show that the maximum d 33 at 320 °C is 192.5 pC / N, which is about 80% larger than the d 33 at room temperature. See Figure 4 .

[0054] Comparative Example 2

[0055] According to the chemical formula 0.75BiFeO3-0.25Ba 1-x Ce xTiO3+y wt.% MnO2, where x = 0, y = 0.05, 0.15 and 0.30, were weighed out. After the mixed powders were ball-milled in anhydrous ethanol medium for 6 h, they were taken out, dried in an oven at 70 °C for 12 h, sieved through a 40-mesh sieve, then put into an alumina crucible, compacted, covered, and heated in a muffle furnace at a heating rate of 10 °C / min to 800 °C for pre-sintering, and held for 4 h to synthesize the main crystal phase. After the furnace was cooled to room temperature, the pre-sintered powders were ground thoroughly, sieved through a 100-mesh sieve, and 3% PVB powder by mass fraction was added as a binder and stirred to granulate in anhydrous ethanol medium. The granulated powders were dry-pressed in a powder tablet press at a pressure of 200 MPa to obtain green bodies in the form of round tablets with a diameter x height of 10 mm x 1 mm. The formed round tablet green bodies were put into a tube furnace and heated at a heating rate of 2 °C / min to 400 °C for degumming, and held for 2 h to remove the PVB binder, and the furnace was cooled to room temperature. Then oxygen was passed through the furnace at a heating rate of 10 °C / min to 1000 °C for sintering, and held for 4 h, and the furnace was cooled to room temperature. The sintered round tablet samples were polished to a thickness of 0.6 mm, and silver electrodes were plated on the polished ceramic tablets. After the silver was burned at 850 °C for 15 min, the ceramic tablets were immediately taken out of the furnace. The silvered ceramic tablets were polarized in silicone oil, with a polarization electric field of 60 kV / cm, a polarization electric field direction perpendicular to the diameter direction of the round tablets, a polarization temperature of 120 °C, a polarization time of 30 min, and a voltage rise speed of 2 V / s. After being taken out, the samples were left to stand in air at room temperature for 48 h.

[0056] The d 33 at room temperature were 99.7 pC / N, 104.6 pC / N and 94.3 pC / N, respectively. The in-situ d 33 at room temperature were 99.7 pC / N, 104.6 pC / N and 94.3 pC / N, respectively. The in-situ d 33 at room temperature were 99.7 pC / N, 104.6 pC / N and 94.3 pC / N, respectively. The in-situ d 33 at room temperature were 99.7 pC / N, 104.6 pC / N and 94.3 pC / N, respectively. The in-situ d Figure 5 .

Claims

1. A method for preparing a bismuth ferrite-barium titanate ceramic having piezoelectric coefficient temperature stability, characterized by: According to the chemical formula of the bismuth ferrite-barium titanate ceramic 0.75BiFeO3-0.25Ba 1-x Ce x TiO3+ y The stoichiometric ratio of the elements in wt.% MnO2 is used to take Fe2O3, BaCO3, CeO2, TiO2 and MnO2, 3 mol% of Bi element is used to take Bi2O3, the mixture is obtained, the pre-sintering powder is obtained by pre-sintering the mixed powder, the granules are obtained by granulating the pre-sintering powder, the green body is obtained by pressing the granules, the bismuth ferrite-barium titanate ceramic is obtained by sequentially performing glue removal and sintering of the green body and then quenching in cooling water. The chemical formula of the bismuth ferrite-barium titanate ceramic is: 0.75 BiFe03-0.25 Ba 1-x Ce x TiO3+ y wt.% MnO2, wherein 0.01 ≤ x ≤ 0.02, 0.10 ≤ y ≤ 0.

15.

2. The method of claim 1, wherein the method is characterized by: The mixing method is wet ball milling, the ball milling medium is anhydrous ethanol, and the ball milling time is 4-8 h.

3. The method of claim 1, wherein the method comprises: preparing a BiFeO3-BaTiO3 ceramic having a piezoelectric coefficient temperature stability. The pre-burning temperature is 750-820℃, the pre-burning time is 3-6 h, and the temperature rising speed is 5-15℃ / min.

4. The method of claim 1, wherein the method is characterized by: After the pre-burning powder is ground and passed through a 100-200 mesh sieve, PVB is added as a binder and stirred and granulated in an anhydrous ethanol medium to obtain granules, wherein the mass fraction of PVB in the granules is 1%-5%.

5. The method for preparing a bismuth ferrite-barium titanate ceramic with piezoelectric coefficient temperature stability according to claim 1, characterized in that: The pressure for the press forming is 100-200 MPa.

6. The method of claim 1, wherein the method is characterized by: The temperature for the glue removal is 400-600℃, the glue removal time is 2-8 h, and the temperature rising speed is 1-5℃ / min.

7. The method of claim 1, wherein the method further comprises: adding a dopant to the mixture of step (a) to form a doped mixture; and sintering the doped mixture to form the BiFeO3-BaTiO3 ceramic. The sintering is performed in an oxygen atmosphere, and the sintering process is as follows: the temperature is raised to 980-1020℃ at a temperature rising speed of 5-15℃ / min, the temperature is kept for 3-6 h, and then the sintering product is immediately taken out of the furnace and quenched in cooling water.

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