A method for preparing texture of high-performance bismuth titanate-barium titanate lead-free piezoelectric ceramic

Abstract

The invention discloses a texture preparation method for high-performance lead-free piezoelectric ceramics of bismuth ferrite-barium titanate. The general formula of the ceramic composition is as follows, where the molar fraction ratio of BiFeO3 and BaTiO3 is 2:1, x, y, t, and m all represent molar fractions, and 0 < x ≤ 0.05, 0 < y ≤ 0.05, 0 < t ≤ 0.05, 0 < m ≤ 0.05. In the sintering stage of the invention, a temperature gradient field is constructed to make the ceramic grains grow texture-directionally, and a textured piezoelectric ceramic with a piezoelectric constant d 33 reaching above 1000 pC / N at 350 °C and a T dr reaching above 350 °C is obtained. The preparation process of the invention is simple, and the prepared ceramic has excellent high-temperature performance and can be applied to the field of high-temperature piezoelectricity.

Description

Technical Field

[0001] This invention relates to the preparation technology of lead-free piezoelectric ceramics, specifically a method for texturing high-performance bismuth ferrite-barium titanate lead-free piezoelectric ceramics. Background Technology

[0002] High-temperature piezoelectric ceramics, as the core component of high-temperature piezoelectric sensors, are crucial for real-time measurement of vibration parameters in critical equipment such as aero-engines and nuclear reactors at temperatures ranging from 200 to 350°C. Currently, bismuth-layered piezoelectric ceramics are the most commonly used core sensing element in international high-temperature piezoelectric sensors. Bismuth-layered lead-free piezoelectric ceramics possess high Curie temperatures and a wide operating temperature range, but their piezoelectric coefficient d... 33 Due to their relatively small size, numerous researchers have modified bismuth layered piezoelectric ceramics using methods such as A-site or B-site ion doping substitution, solid solution formation, and symbiotic structure formation, hoping to enhance their piezoelectric activity while maintaining a high Curie temperature. However, the improvement effect has not been significant, and the piezoelectric coefficient d of modified bismuth layered ceramic oxides with Curie temperatures above 500℃ is relatively low. 33 The Curie temperature T of bismuth layered ceramic oxides is typically around 18 pC / N, with a piezoelectric coefficient greater than 20 pC / N. C Most of them are below 400℃, which limits the sensitivity and high-frequency stability of high-temperature devices.

[0003] Limited by the difficulty of combining the high piezoelectric properties and high Curie temperature of piezoelectric ceramics, while possessing high T... dr The development and application of piezoelectric ceramics with high piezoelectric activity have not yielded significant breakthroughs. The bismuth scandate-lead titanate (BS-PT) system is an exception; this system achieves a wide operating temperature range (T0) by synergistically controlling the R / T phase ratio, microstructure, and doping elements. dr Excellent piezoelectric properties are obtained within ~300℃. 33 ~460pC / N. However, with increasing attention to environmental issues and sustainable development, piezoelectric ceramics that use high proportions of toxic elements such as lead in their manufacturing process are gradually being replaced by lead-free piezoelectric ceramics, which is becoming a mainstream market application trend.

[0004] Bismuth ferrite-barium titanate (BF-BT) ceramics, as a type of perovskite-structured lead-free piezoelectric ceramic, have a high Curie temperature of 830℃. C and 90~100μC / cm 2 spontaneous polarization intensity P s This is key to breakthroughs in high-temperature piezoelectric applications, but the piezoelectric properties of this type of ceramic prepared by conventional methods are generally inferior to those of lead-based piezoelectric ceramics. This is due to the significant difference in sintering temperatures between BF (850℃) and BT (1450℃), the high volatility of Bi at high temperatures, and the influence of Fe... 3+ Ions to Fe2+ Changes in ions can create defects such as oxygen vacancies and tend to produce heterogeneous phases, such as Bi₂O₃, Bi₂Fe₄O₉, and Bi. 25 FeO 39 This reduces the piezoelectric properties of the ceramic. Solving this problem requires addressing the sintering process, as the sintering regime, atmosphere, additives, and cooling method all significantly influence the ceramic's performance. In recent years, the texturing process of piezoelectric ceramics has received widespread attention. Optimizing the piezoelectric properties of ceramics through texturing essentially utilizes the anisotropic nature of piezoelectric properties. By controlling the preparation parameters or conditions, the material is preferentially grown along crystallographic directions with higher piezoelectric performance, thereby optimizing its properties. Therefore, applying texturing technology to BF-BT ceramics, through appropriate orientation texturing, to increase the piezoelectric properties and stability of this ceramic system, holds great research and application potential. Summary of the Invention

[0005] To address the challenge of simultaneously achieving high voltage performance and high temperature stability, this invention proposes a texturing preparation method for high-performance bismuth ferrite-barium titanate ceramics. This invention introduces B-site heterovalent cations into the BiFeO3-BaTiO3 ceramic system, specifically by adding Bi(Zn) ions. 0.5 Ti 0.5 O3 and BiAlO3 were used to regulate their phase and domain structures. To achieve textured grain growth, features such as... were incorporated during the sintering process. Figure 1 The temperature gradient field shown induces directional grain texture growth, improves anisotropy, and after sintering, according to... Figure 2 The cross-sectional cutting and polarization are shown. Simultaneously, this invention adds sintering aids to the formulation, which effectively reduces the sintering temperature, increases the density of the ceramic, and facilitates the textured growth of the ceramic; as shown... Figure 3 As shown, the textured piezoelectric ceramic prepared using the technology of this invention achieves an in-situ quasi-static depolarization temperature of T. dr =350℃, and the piezoelectric constant d when operating at 200℃ 33 It can reach 400 pC / N, and the piezoelectric constant d at 350℃ is... 33 Maintaining a value above 1000 pC / N, this represents the optimal piezoelectric performance achievable by all publicly reported piezoelectric ceramic systems operating at temperatures above 300°C.

[0006] The technical solution to achieve the objective of this invention is:

[0007] A high-performance bismuth ferrite-barium titanate lead-free piezoelectric ceramic, with the following general formula: In the formula, the molar fraction ratio of BiFeO3 and BaTiO3 is 2:1, where x, y, t, and m all represent molar fractions, and 0 < x ≤ 0.05, 0 < y ≤ 0.05, 0 < t ≤ 0.05, 0 < m ≤ 0.05.

[0008] The texture preparation method of the high-performance bismuth ferrite-barium titanate lead-free piezoelectric ceramic includes the following steps:

[0009] 1) Using analytically pure Bi2O3, Fe2O3, BaCO3, TiO2, ZnO, Al2O3, Li2CO3, and MnO2 as raw materials,配料 according to the chemical composition, where 0 < x ≤ 0.05, 0 < y ≤ 0.05, 0 < t ≤ 0.05, 0 < m ≤ 0.05. After ball-milling the mixed powder in absolute ethanol for 24 h, take it out and place it in an oven to dry at 100 °C for 12 h, pass through a 100-200 mesh sieve, then put it into an alumina crucible, compact it and cover it, and then put it into a muffle furnace and heat it at a heating rate of 120 °C / h to 800-820 °C for pre-sintering, keep it warm for 4 h to synthesize the main crystal phase, take it out after cooling to room temperature with the furnace and reserve it for use;

[0010] 2) Grind the pre-sintered powder thoroughly, pass through a 100-200 mesh sieve, add a PVA solution with a mass concentration of 8% for granulation, and extrude it into a cylindrical green body with a diameter × height of 10 mm × 20 mm in a powder press at a pressure of 20 MPa;

[0011] 3) Put the formed cylindrical green body into a furnace with a set temperature gradient field on both sides. The set temperature of the first temperature zone on one side of the furnace is T1, and the set temperature of the second temperature zone on the other side of the furnace is T2, 850 °C ≤ T1 ≤ 950 °C, 950 °C ≤ T2 ≤ 1050 °C; Slowly raise the temperature of both temperature zones to 600 °C at a heating rate of 30 °C / h, keep it warm for 3 h to remove the binder; Then quickly raise the temperature of the first temperature zone to T1 and the second temperature zone to T2 at a heating rate of 300 °C / h, keep it warm for 4 h for sintering, then quickly cool it to 800 °C at a cooling rate of 300 °C / h and keep it warm for 1 h, cut off the power, and cool it to room temperature with the furnace;

[0012] 4) Cut the sintered cylindrical sample into circular flakes along the radial direction, grind and polish the surface of the circular flake samples into smooth slices with a thickness of 0.5 mm; Plate silver electrodes on the polished ceramic slices and burn the silver at 650 °C for 15 min;

[0013] 5) Place the ceramic slices after silver burning in silicone oil for polarization. The polarization electric field is 8000 V / mm, the polarization electric field direction is perpendicular to the radial direction of the circular slice, the polarization temperature is 120 °C, and the polarization time is 20 min. Take it out and let it stand in the air at room temperature for 24 h. Then test the performance.

[0014] The positive effects of this invention are:

[0015] This invention simultaneously enhances intrinsic and extrinsic piezoelectric contributions by introducing B-site heterovalent cations to regulate phase and domain structures. Furthermore, it utilizes a temperature gradient field during the sintering process of the piezoelectric ceramic to increase the preferred orientation ratio of the domain structure, resulting in samples with superior piezoelectric properties compared to randomly oriented ceramics. Simultaneously, sintering aids are added to the formulation to effectively reduce sintering temperature and shorten sintering time, thereby increasing sintering orientation and promoting the texturing process. The ceramics prepared using this invention... Textured lead-free piezoelectric ceramics possess both high piezoelectric properties and high operating temperature, with a piezoelectric constant d when operating at temperatures above 350°C. 33 It can reach over 1000pC / N, T dr It can reach temperatures above 350℃; in addition, a wide working range with good temperature stability of 110℃ was obtained around the working temperature of 150℃, within which the sample still maintains a high piezoelectric coefficient of 400pC / N.

[0016] The above performance exceeds the upper limit of BF-BT-based piezoelectric ceramics, and is also the highest piezoelectric performance that can be achieved when operating at high temperatures above 300°C among all publicly reported piezoelectric ceramic systems. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the principle of applying the sintering temperature gradient field to the lead-free piezoelectric ceramic sample of the present invention.

[0018] Figure 2 This is a schematic diagram of a cross-sectional cut of the lead-free piezoelectric ceramic sintered sample of the present invention; the hollow arrow indicates the radial cutting direction, and the black arrow indicates the polarization electric field direction.

[0019] Figure 3 Td of the lead-free piezoelectric ceramic sample prepared in this invention 33 In-situ depolarization curve.

[0020] In the figure, 1. Furnace body 1-1. First furnace baffle 1-2. Second furnace baffle 1-3. First temperature zone 1-4. Second temperature zone 2. Partition layer 3. Sample. Detailed Implementation

[0021] The present invention will be further illustrated below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] like Figure 1As shown, the tube furnace used in step (3) of the embodiment is a two-temperature zone tube furnace, including a first furnace baffle 1-1 and a second furnace baffle 1-2 set at both ends of the furnace body 1; the sample 3 is placed in the hollow part of the partition layer 2, and the sample 3 and the partition layer 2 are placed in the middle of the furnace body 1. The partition layer 2 divides the interior of the furnace body 1 into two temperature zones, namely the first temperature zone 1-3 and the second temperature zone 1-4. The two ends of the sample 3 are respectively located in the first temperature zone 1-3 and the second temperature zone 1-4.

[0023] The partition layer 2 is a circular cylindrical body, and the sample 3 is placed in the hollow part of the circular cylindrical body. The partition layer 2 serves to isolate the two temperature zones and maintain the temperature gradient (temperature difference) at both ends of the sample.

[0024] Example 1:

[0025] A high-performance bismuth ferrite-barium titanate textured lead-free piezoelectric ceramic, with the chemical formula:

[0026]

[0027] The method for preparing its texture is as follows:

[0028] (1) Using analytically pure Bi₂O₃, Fe₂O₃, BaCO₃, TiO₂, ZnO, Al₂O₃, Li₂CO₃, and MnO₂ as raw materials, according to... The chemical composition was used to prepare the ingredients. The mixed powder was ball-milled for 24 hours with anhydrous ethanol as the medium. After that, it was taken out and placed in an oven to dry at 100°C for 12 hours. It was then passed through a 150-mesh sieve, placed in an alumina crucible, compacted and covered. It was then placed in a muffle furnace and heated to 800°C at a heating rate of 120°C / h 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.

[0029] (2) The pre-calcined powder is thoroughly ground, passed through a 150-mesh sieve, and granulated by adding a PVA solution with a mass concentration of 8%. The powder is then extruded in a powder press at a pressure of 20 MPa to obtain a cylindrical blank with a diameter × height of 10 mm × 20 mm.

[0030] (3) Figure 1 As shown, the formed cylindrical blank sample 3 is placed in a tube furnace with temperature gradient fields set on both sides. The first temperature zone 1-3 on one side of the tube furnace is set to a temperature of T1 = 910℃, and the second temperature zone 1-4 on the other side is set to a temperature of T2 = 990℃. Both temperature zones are slowly heated to 600℃ at a heating rate of 30℃ / h and held for 3h to remove the binder. Then, the first temperature zone 1-3 is rapidly heated to T1 = 910℃ and the second temperature zone 1-4 is rapidly heated to T2 = 990℃ at a heating rate of 300℃ / h and held for 4h for sintering. Then, the temperature is rapidly cooled to 800℃ at a cooling rate of 300℃ / h and held for 1h. The power is then turned off, and the furnace is cooled to room temperature.

[0031] (4) Figure 2 As shown, the sintered cylindrical sample 3 was cut into circular pieces along the radial direction. The surface of the circular pieces was ground and polished into a thin sheet with smooth surfaces and a thickness of 0.5 mm. Silver electrodes were plated on the polished ceramic sheet and fired at 650°C for 15 min.

[0032] (5) The silver-fired ceramic sheet is placed in silicone oil for polarization. The polarization electric field is 8000 V / mm, and the direction of the polarization electric field is perpendicular to the radial direction of the disc. Figure 2 As shown, the polarization temperature was 120℃, the polarization time was 20 min, and after removal, it was left to stand at room temperature and in air for 24 h. Then the performance was tested again.

[0033] The performance test results are as follows:

[0034]

[0035] Example 2:

[0036] A high-performance bismuth ferrite-barium titanate textured lead-free piezoelectric ceramic, with the chemical formula:

[0037]

[0038] The texture preparation method is the same as in Example 1, except that:

[0039] In step (1) according to

[0040] The ingredients are formulated based on their chemical composition;

[0041] In step (3), T1 = 930℃ and T2 = 1000℃.

[0042] The performance test results are as follows:

[0043]

[0044] Example 3:

[0045] A high-performance bismuth ferrite-barium titanate textured lead-free piezoelectric ceramic, with the chemical formula:

[0046]

[0047] The texture preparation method is the same as in Example 1, except that:

[0048] In step (1) according to

[0049] The ingredients are formulated based on their chemical composition;

[0050] In step (3), T1 = 940℃ and T2 = 1010℃.

[0051] The performance test results are as follows:

[0052]

[0053] Example 4:

[0054] A high-performance bismuth ferrite-barium titanate textured lead-free piezoelectric ceramic, with the chemical formula:

[0055]

[0056] The texture preparation method is the same as in Example 1, except that:

[0057] In step (1) according to

[0058] The ingredients are formulated based on their chemical composition;

[0059] In step (3), T1 = 940℃ and T2 = 1020℃.

[0060] The performance test results are as follows:

[0061]

[0062] Example 5:

[0063] A high-performance bismuth ferrite-barium titanate textured lead-free piezoelectric ceramic, with the chemical formula:

[0064]

[0065] The texture preparation method is the same as in Example 1, except that:

[0066] In step (1) according to

[0067] The ingredients are formulated based on their chemical composition;

[0068] In step (3), T1 = 950℃ and T2 = 1030℃.

[0069] The performance test results are as follows:

[0070]

[0071] The upper and lower limits and ranges of the components and the process parameters listed in this invention can all achieve this invention, and will not be listed one by one here.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for texturing high-performance bismuth ferrite-barium titanate lead-free piezoelectric ceramics, characterized in that, The preparation method includes setting a temperature range to construct a temperature gradient field in order to induce grain textured directional growth and improve anisotropy; The preparation method includes the following steps: 1) Using analytically pure Bi₂O₃, Fe₂O₃, BaCO₃, TiO₂, ZnO, Al₂O₃, Li₂CO₃, and MnO₂ as raw materials, according to... BiFeO3- BaTiO3+xBi(Zn 0.5 Ti 0.5 The chemical composition of O3+yBiAlO3+tLi2CO3+mMnO2 was used to prepare the raw materials, where 0 < x ≤ 0.05, 0 < y ≤ 0.05, 0 < t ≤ 0.05, and 0 < m ≤ 0.

05. The mixed powder was ball-milled with anhydrous ethanol for 24 hours, then placed in an oven and dried at 100℃ for 12 hours. After passing through a 100~200 mesh sieve, it was placed in an alumina crucible, compacted, and covered. Then it was placed in a muffle furnace and heated to 800~820℃ at a heating rate of 120℃ / h for pre-calcination and held for 4 hours to synthesize the main crystalline phase. After cooling to room temperature with the furnace, it was taken out for use. 2) Grind the pre-calcined powder thoroughly, pass it through a 100-200 mesh sieve, add a PVA solution with a mass concentration of 8% for granulation, and extrude it in a powder tablet press at a pressure of 20MPa to obtain a cylindrical blank with a diameter × height of 10mm × 20mm. 3) Place the formed cylindrical blank into a furnace with temperature gradient fields on both sides. The first temperature zone on one side of the furnace is set to temperature T1, and the second temperature zone on the other side of the furnace is set to temperature T2. 850℃≤T1≤950℃, 950℃≤T2≤1050℃. Slowly raise both temperature zones to 600℃ at a heating rate of 30℃ / h, hold for 3h to remove the binder. Then, rapidly raise the first temperature zone to T1 and the second temperature zone to T2 at a heating rate of 300℃ / h, hold for 4h for sintering. Then, rapidly cool to 800℃ at a cooling rate of 300℃ / h, hold for 1h, turn off the power, and let the furnace cool to room temperature. 4) Cut the sintered cylindrical sample into circular pieces along the radial direction, grind and polish the surface of the circular pieces into thin sheets with smooth surfaces and a thickness of 0.5 mm; plate silver electrodes on the polished ceramic sheets and fire them at 650℃ for 15 min. 5) After the silver-burning ceramic sheet is placed in silicone oil for polarization, the polarization electric field is 8000V / mm, the polarization electric field direction is perpendicular to the radial direction of the disc, the polarization temperature is 120℃, the polarization time is 20min, and after removal, it is left to stand in room temperature and air for 24h.

2. The method for preparing the texture of high-performance bismuth ferrite-barium titanate lead-free piezoelectric ceramics according to claim 1, characterized in that, The preparation method includes the following steps: (1) Using analytically pure Bi2O3, Fe2O3, BaCO3, TiO2, ZnO, Al2O3, Li2CO3 and MnO2 as raw materials, according to BiFeO3- BaTiO3+0.01Bi(Zn 0.5 Ti 0.5 The chemical composition of O3+0.01BiAlO3+0.002Li2CO3+0.003MnO2 was used to prepare the raw materials. The mixed powder was ball-milled with anhydrous ethanol for 24 hours. After that, it was taken out and placed in an oven to dry at 100℃ for 12 hours. It was then passed through a 150-mesh sieve, compacted and covered in an alumina crucible, and then placed in a muffle furnace and heated to 800℃ at a heating rate of 120℃ / h for pre-calcination. The temperature was held for 4 hours to synthesize the main crystalline phase. After cooling to room temperature in the furnace, it was taken out for use. (2) The pre-calcined powder is thoroughly ground, passed through a 150-mesh sieve, and granulated by adding a PVA solution with a mass concentration of 8%. The powder is then extruded in a powder press at a pressure of 20 MPa to obtain a cylindrical blank with a diameter × height of 10 mm × 20 mm. (3) Place the formed cylindrical blank sample into a tube furnace with temperature gradient fields on both sides. The first temperature zone on one side of the tube furnace is set to T1=910℃ and the second temperature zone is set to T2=990℃. Slowly raise both temperature zones to 600℃ at a heating rate of 30℃ / h and hold for 3h to remove the glue. Then raise the first temperature zone to T1=910℃ and the second temperature zone to T2=990℃ at a heating rate of 300℃ / h and hold for 4h for sintering. Then lower the temperature to 800℃ at a cooling rate of 300℃ / h and hold for 1h. Turn off the power and let the furnace cool to room temperature. (4) Cut the sintered cylindrical sample into circular pieces along the radial direction, grind and polish the surface of the circular pieces into thin sheets with smooth surfaces and a thickness of 0.5 mm; plate silver electrodes on the polished ceramic sheets and heat them at 650℃ for 15 min. (5) The silver-burned ceramic sheet is placed in silicone oil for polarization. The polarization electric field is 8000V / mm, the polarization electric field direction is perpendicular to the radial direction of the disc, the polarization temperature is 120℃, the polarization time is 20min, and after removal, it is left to stand in room temperature and air for 24h.

3. The ceramic prepared by the texturing method of the high-performance bismuth ferrite-barium titanate lead-free piezoelectric ceramic according to claim 1 has the following general composition formula: BiFeO3- BaTiO3+xBi(Zn 0.5 Ti 0.5 The equation is: O3+yBiAlO3+tLi2CO3+mMnO2, where the mole fraction ratio of BiFeO3 and BaTiO3 is 2:1, x, y, t and m all represent mole fractions, and 0 < x ≤ 0.05, 0 < y ≤ 0.05, 0 < t ≤ 0.05, 0 < m ≤ 0.

05.

4. The ceramic prepared by the texturing method of the high-performance bismuth ferrite-barium titanate lead-free piezoelectric ceramic according to claim 2 has the following chemical formula: BiFeO3- BaTiO3+0.01Bi(Zn 0.5 Ti 0.5 )O3 + 0.01BiAlO3 + 0.002Li2CO3 + 0.003MnO2。

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