Method for improving piezoelectric response of sodium bismuth titanate-barium titanate ceramic

Abstract

The invention belongs to the field of functional material application, and relates to a method for improving piezoelectric response of sodium bismuth titanate-barium titanate ceramics. According to the invention, the sintered sodium bismuth titanate-barium titanate series piezoelectric ceramic is cooled from high temperature to room temperature at a very slow rate, so that the influence of atom occupation complexity on the characteristics of a polar region can be fully reflected, and the heterogeneity of polarization intensity (size and direction) between polar nano micro-regions in the structure is improved; the energy barrier of polarization intensity steering in the system is reduced, the change of the polarization intensity in an external field is facilitated, and the purpose of improving the piezoelectric response of the sodium bismuth titanate-barium titanate ceramic is achieved.

Description

Technical Field

[0001] The invention belongs to the field of functional material applications, and in particular relates to a method for improving the piezoelectric response of a piezoelectric material. Background Art

[0002] Piezoelectric materials play an important role in electronic components such as sensors, actuators, and transducers. These functional applications originate from the piezoelectric response (mechanical-electric coupling effect) in the material under external excitation, which manifests as electrostrain response or stress-induced electroresponse. Since the second half of the last century, environmentally friendly lead-free piezoelectric materials have become the research target of many scientists in the field. Representative systems include potassium sodium niobate, barium titanate, sodium / potassium bismuth titanate, and bismuth ferrite. At present, lead-free piezoelectric materials are not enough to replace commercial lead-based piezoelectric materials. The main reason is that the piezoelectric response and thermal stability cannot be comparable to those of lead-containing piezoelectric materials. At present, except for the sodium / potassium bismuth titanate system, the piezoelectric responses of the other three material systems have been improved to a level comparable to that of lead-containing piezoelectric materials (400-600pC / N), but the thermal stability is still significantly lower than that of lead-containing piezoelectric materials. For sodium / potassium bismuth titanate ceramics, only a few research reports have obtained a piezoelectric response of 200-225pC / N. Therefore, exploring methods to improve the piezoelectric response of sodium / potassium bismuth titanate ceramics remains a research hotspot in the current field.

[0003] Among the various technical solutions for improving the piezoelectric properties of sodium bismuth titanate / potassium ceramics, the main focus is on adjusting the components, and constructing a special formula to adjust the microstructure and thus improve the piezoelectric response. In recent years, quenching has been used as a way to adjust the piezoelectric properties of piezoelectric ceramics, and the resulting changes in piezoelectric performance are: reducing the piezoelectric response and improving the piezoelectric thermal stability. Considering that the essence of this technical solution is to perform subsequent heat treatment on piezoelectric ceramics at an extremely fast cooling rate, if the opposite process is taken: performing subsequent heat treatment on piezoelectric ceramics at an extremely slow cooling rate, the piezoelectric properties of the ceramics may be optimized without changing the formula. Recently, there have been reports in the field that slow cooling affects piezoelectric properties, but the results in the report show that the size of the piezoelectric response is not affected by the cooling rate (quenching / normal speed / slow speed) of the heat treatment process, which brings a layer of fog to the idea of ​​improving piezoelectric performance through subsequent heat treatment. It is not clear whether it is a problem of ideas or a problem of material components. Summary of the invention

[0004] In view of this, the present invention provides a method for improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics.

[0005] It should be noted that the perovskite type (ABO 3) structure of sodium bismuth titanate-barium titanate piezoelectric ceramics, the A position in its crystal structure is often occupied by different atoms. The complexity of this atomic position will affect the periodic characteristics of the crystal structure, and will further affect the characteristics of the polar regions formed in the low-temperature range structure, such as the size of the polar regions, the polarization intensity, and the distribution characteristics between the polar regions in the grains. By cooling the sintered sodium bismuth titanate-barium titanate piezoelectric ceramics from high temperature to room temperature at an extremely slow rate, the influence of the atomic position complexity on the characteristics of the polar regions can be fully reflected, the heterogeneity of the polarization intensity (size and direction) between the polar nano-microregions in the structure can be improved, the energy barrier for the polarization intensity turning in the system can be reduced, and it is beneficial to the change of the polarization intensity under the external field, so as to achieve the purpose of improving the piezoelectric response of sodium bismuth titanate ceramics.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics. By cooling the sintered sodium bismuth titanate-barium titanate piezoelectric ceramics from high temperature to room temperature at an extremely slow rate, the influence of atomic occupancy complexity on the characteristics of polar regions can be fully reflected, the heterogeneity of polarization intensity (size and direction) between polar nano-microregions in the structure can be improved, the energy barrier for polarization intensity steering in the system can be reduced, and the change of polarization intensity under an external field can be facilitated, so as to achieve the purpose of improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics.

[0008] Furthermore, the sodium bismuth titanate-barium titanate ceramics have a perovskite type (ABO 3 ) structure, by subjecting the sintered sodium bismuth titanate-barium titanate piezoelectric ceramics to subsequent heat treatment, first raising it to a certain high temperature and then keeping it warm for a period of time, and then dropping it from high temperature to room temperature at an extremely slow rate so that the influence of the complexity of the A-site atomic occupancy on the polar region formation process can be fully reflected, the heterogeneity of the polarization intensity (size and direction) between the polar nano-microregions in the structure is improved, the energy barrier for the polarization intensity turning in the system is reduced, which is beneficial to the change of the polarization intensity under the external field, so as to achieve the purpose of improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics.

[0009] It should be noted that perovskite type (ABO 3 ) structure such as Figure 1 As shown, A is the vertex position of the cubic skeleton, which is occupied by the same or multiple atoms; B is the body center position of the cubic skeleton, which can also be occupied by the same or multiple atoms; O atoms occupy the six face center positions of the cubic skeleton. For sodium bismuth titanate-barium titanate ceramics, the atoms occupying the A position are Na, Bi, and Ba atoms. They occupy the same position in the lattice but show different valence states and ionic radii; the atom occupying the B position is Ti, so the chemical formula of sodium bismuth titanate-barium titanate ceramics can be written as (Na 0.5 Bi0.5 ) 1-x Ba x TiO 3 .

[0010] For ceramic materials after high-temperature sintering, only some ions with a very small radius in the structure can change their positions (migrate) within the range below the sintering temperature. Unlike simple material systems (such as barium titanate), the lattice site A in sodium bismuth titanate-barium titanate ceramics is often occupied by different atoms, resulting in the local inhomogeneity of the lattice potential field. Usually, during the sintering process of piezoelectric ceramics, the cooling stage generally adopts a rate of 3 to 10 ° C / minute. In the cooling process at the above general cooling rate, when passing through the ceramic phase transition temperature range, the local inhomogeneity of the lattice potential field does not have time to have a significant impact on the formed polar region, and this feature is not fully reflected in the low-temperature phase. On the contrary, if the phase transition temperature range is passed at an extremely low cooling rate, the low-temperature phase formed has obvious inhomogeneities related to the complexity of atomic occupancy, such as a significant increase in the heterogeneity level of local polarity. The increase in local polar heterogeneity is generally accompanied by an increase in the average free energy level of the system, making it easier to turn between different polarization directions, which is conducive to obtaining a higher piezoelectric response.

[0011] Furthermore, the chemical formula of the sodium bismuth titanate-barium titanate ceramic is (Na 0.5 Bi 0.5 ) 1-x Ba x TiO 3 , x=0.02,0.06,0.08,0.10,0.15,0.20,0.25.

[0012] Furthermore, the peak temperature and holding time of the heat treatment are 900-1000°C / 1-3 hours; the heating rate is 3-10°C / min; and the cooling rate is 0.05-0.2°C / min.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention performs heat treatment at an extremely low rate of cooling without changing the target component formula to improve the piezoelectric response of sodium bismuth titanate-barium titanate ceramics. This design is different from the mainstream component design routes such as doping substitution and multi-component solid solution. Compared with this design, it has the following advantages:

[0015] (1) The obtained piezoelectric response is high, reaching more than 220pC / N; (2) There is no need for special design of the components, the process is simple, and the operability is strong, which provides a feasible option for improving the piezoelectric response of sodium bismuth titanate piezoelectric materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0017] Figure 1 It is a perovskite type (ABO 3 ) structure diagram. A and B represent the vertex position and body center position of the cubic skeleton respectively, O is an atom, and A1, A2, and A3 represent different types of atoms.

[0018] Figure 2 It is a piezoelectric ceramic (Na 0.5 Bi 0.5 ) 1-x Ba x TiO 3 , x=0.02, 0.06, 0.08, 0.10, 0.15, 0.20, 0.25 abbreviated as: Comparison between the characteristic diffraction peaks in the XRD pattern of NBBT100x) sample at room temperature.

[0019] Figure 3 It is a piezoelectric ceramic (Na2O3) with quenched sample (QS), normally cooled sample (NS) and slowly cooled sample (SC). 0.5 Bi 0.5 ) 1-x Ba x TiO 3 ,x=0.02,0.06,0.08,0.10,0.15,0.20,0.25 (abbreviated as: NBBT100x) Comparison of dielectric and piezoelectric properties of samples at room temperature. (a) Frequency dependence of room temperature dielectric constant (ε r ~f) Fitting straight line ε r ~ln(f). The slope of this fitting straight line reflects the heterogeneity between polar microdomains in the structure. The larger the slope, the stronger the heterogeneity, and vice versa. (b) Room temperature piezoelectric coefficient, the ceramic is polarized under an electric field of 4 kV / mm.

[0020] Figure 4It is a piezoelectric ceramic (when Sr, Ba, Nb, V are doped (Na 0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 Ceramics, abbreviated as: comparison between the characteristic diffraction peaks in the XRD pattern of doped NBBT6) samples at room temperature.

[0021] Figure 5 It is a piezoelectric ceramic (when Sr, Ba, Nb, V are doped (Na 0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 Comparison of piezoelectric coefficients of ceramics (abbreviated as: doped NBBT6) samples at room temperature; Note: ceramics are polarized under an electric field of 4 kV / mm. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The word "embodiment" used here as an "exemplary" does not necessarily mean that any embodiment described is superior to or better than other embodiments. Unless otherwise specified, the performance index tests in the embodiments of this application are performed using conventional test methods in the art. It should be understood that the terms described in this application are only used to describe specific implementation methods and are not used to limit the content disclosed in this application.

[0024] Unless otherwise specified, the technical and scientific terms used in this document have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs; other experimental methods and technical means not specifically specified in this application refer to experimental methods and technical means commonly used by ordinary technicians in this field.

[0025] In order to better illustrate the content of the present application, numerous specific details are provided in the specific examples below. It should be understood by those skilled in the art that the present application can also be implemented without certain specific details. In the embodiments, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present application.

[0026] Under the premise of no conflict, the technical features disclosed in the embodiments of the present application can be combined arbitrarily, and the resulting technical solutions belong to the contents disclosed in the embodiments of the present application.

[0027] In order to better understand the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as a limitation of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above invention content are also considered to fall within the protection scope of the present invention.

[0028] The design described in this patent, which is to improve the piezoelectric response of sodium bismuth titanate-barium titanate ceramics by cooling at an extremely low rate without changing the formula of the target components, is a general method for improving the piezoelectric response of piezoelectric ceramics and is applicable to ferroelectric ceramic materials. 0.5 Bi 0.5 TiO 3 -BaTiO 3 ) to illustrate the feasibility of this design.

[0029] Embodiment 1: (Na 0.5 Bi 0.5 ) 0.98 Ba 0.02 TiO 3 , abbreviated as: NBBT2 ceramic

[0030] NBBT2 ceramic samples were prepared by conventional solid phase synthesis. 0.5 Bi 0.5 ) 0.98 Ba 0.02 TiO 3 ) in the metering ratio of adding Bi 2 O 3 , Na 2 CO 3 , BaCO 3 , TiO 2(Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder of NBBT2. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the weight of the powder as a binder (5% concentration of polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep it at a temperature of 1100℃-1220℃ for 2 hours for sintering, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0031] For the samples with rapid cooling, the samples with polished and parallel two end surfaces were heated to 900°C and kept at this temperature for 1 hour, then taken out directly from the furnace and rapidly cooled to room temperature in air. The ceramic samples obtained by this method were recorded as QS samples.

[0032] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0033] For subsequent electrical testing, silver electrodes were prepared on both ends of the QS, SC and NS samples, and then the ceramics with prepared electrodes were polarized at 7 kV / mm electric field for 5 min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0034] like Figure 2 As shown in (a), the diffraction peaks of the SC sample of NBBT2 show a higher degree of symmetry compared to the NS sample, but the difference is not very large. Figure 3 As shown in (a), compared with the QS-like, the NS and SC-like of NBBT2 exhibit enhanced microdomain polar heterogeneity, which can be determined by the dielectric constant (ε r ) shows that compared with the NS sample, the SC sample of NBBT2 shows little change in the characteristics of the polar micro-region. The change of dielectric constant with frequency can be fitted into ε r ~ln(f), the slope of the straight line reflects the consistency (coherence) of the response of the polarization intensity of the polar micro-region to the change of the external electric field. The larger the slope, the more heterogeneous the polarity of the micro-region is, and vice versa, the more homogeneous the polarity of the micro-region is. Figure 3 As shown in (b), in comparison, the trend of the room temperature piezoelectric coefficient of NBBT2 sample under the three cooling rates is that the SC sample shows an increase, followed by NS and QS.

[0035] Embodiment 2: (Na 0.5Bi 0.5 ) 0.94 Ba 0.06 TiO 3 , abbreviated as: NBBT6 ceramic

[0036] NBBT6 ceramic samples were prepared by conventional solid phase synthesis. 0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 ) in the metering ratio of adding Bi 2 O 3 , Na 2 CO 3 , BaCO 3 , TiO 2 (Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder of NBBT6. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the weight of the powder as a binder (5% concentration of polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep warm at a temperature of 1100℃-1220℃ for 2 hours to sinter, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0037] For the samples with rapid cooling, the samples with polished and parallel two end surfaces were heated to 900°C and kept at this temperature for 1 hour, then taken out directly from the furnace and rapidly cooled to room temperature in air. The ceramic samples obtained by this method were recorded as QS samples.

[0038] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0039] For subsequent electrical testing, silver electrodes were prepared on both ends of the QS, SC and NS samples. The ceramics with prepared electrodes were then polarized at 7 kV / mm electric field for 5 min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0040] like Figure 2 As shown in (b), compared with the NS sample, the diffraction peak of the SC sample of NBBT6 shows a higher degree of symmetry, and the tetragonal symmetry is significantly weakened (see the diffraction peak near 46°). Figure 3As shown in (a), compared with the QS sample, both the NS and SC samples of NBBT6 show enhanced heterogeneity in polar microdomains, which can be determined by the dielectric constant (ε r The frequency (f) dependence of the dielectric constant can be fitted into ε r ~ln(f), the slope of the straight line reflects the consistency (coherence) of the response of the polarization intensity of the polar micro-region to the change of the external electric field. The larger the slope, the more heterogeneous the polarity of the micro-region is, and vice versa, the more homogeneous the polarity of the micro-region is. Figure 3 As shown in (b), in comparison, under the three cooling rates, the trend of the room temperature piezoelectric coefficient of NBBT6 sample is that the SC sample shows an increase, followed by NS and QS.

[0041] Embodiment 3: (Na 0.5 Bi 0.5 ) 0.92 Ba 0.08 TiO 3 , abbreviated as: NBBT8 ceramic

[0042] NBBT8 ceramic samples were prepared by conventional solid phase synthesis. 0.5 Bi 0.5 ) 0.92 Ba 0.08 TiO 3 ) in the metering ratio of adding Bi 2 O 3 , Na 2 CO 3 , BaCO 3 , TiO 2 (Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder with the component NBBT8. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the weight of the powder as a binder (5% concentration of polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep it at a temperature of 1100℃-1220℃ for 2 hours for sintering, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0043] For the samples with rapid cooling, the samples with polished and parallel two end surfaces were heated to 900°C and kept at this temperature for 1 hour, then taken out directly from the furnace and rapidly cooled to room temperature in air. The ceramic samples obtained by this method were recorded as QS samples.

[0044] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0045] For subsequent electrical testing, silver electrodes were prepared on both ends of the QS, SC and NS samples. The ceramics with prepared electrodes were then polarized at 7 kV / mm electric field for 5 min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0046] like Figure 2 As shown in (b), compared with the NS sample, the diffraction peak of the SC sample of NBBT10 shows a higher degree of symmetry, and the tetragonal symmetry is significantly weakened (see the diffraction peak near 46°). Figure 3 As shown in (a), compared with the QS sample, both the NS and SC samples of NBBT8 show enhanced heterogeneity in polar microdomains, which can be determined by the dielectric constant (ε r The frequency (f) dependence of the dielectric constant can be fitted into ε r ~ln(f), the slope of the straight line reflects the consistency (coherence) of the response of the polarization intensity of the polar micro-region to the change of the external electric field. The larger the slope, the more heterogeneous the polarity of the micro-region is, and vice versa, the more homogeneous the polarity of the micro-region is. Figure 3 As shown in (b), in comparison, under the three cooling rates, the trend of the room temperature piezoelectric coefficient of NBBT8 sample is that the SC sample shows an increase, followed by NS and QS.

[0047] Embodiment 4: (Na 0.5 Bi 0.5 ) 0.90 Ba 0.10 TiO 3 , abbreviated as: NBBT10 ceramic

[0048] The NBBT10 ceramic sample was prepared by conventional solid phase synthesis method. 0.5 Bi 0.5 ) 0.90 Ba 0.10 TiO 3 ) in the metering ratio of adding Bi 2 O 3 , Na 2 CO 3 , BaCO 3 , TiO 2(Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder of NBBT10. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the weight of the powder binder (5% concentration of polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep it at a temperature of 1100℃-1220℃ for 2 hours for sintering, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0049] For the samples with rapid cooling, the samples with polished and parallel two end surfaces were heated to 900°C and kept at this temperature for 1 hour, then taken out directly from the furnace and rapidly cooled to room temperature in air. The ceramic samples obtained by this method were recorded as QS samples.

[0050] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0051] For subsequent electrical testing, silver electrodes were prepared on both ends of the QS, SC and NS samples. The ceramics with prepared electrodes were then polarized at 7 kV / mm electric field for 5 min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0052] like Figure 2 As shown in (b), compared with the NS sample, the diffraction peak of the SC sample of NBBT10 shows a higher degree of symmetry, and the tetragonal symmetry is significantly weakened (see the diffraction peak near 46°). Figure 3 As shown in (a), compared with the QS sample, both the NS and SC samples of NBBT10 show enhanced heterogeneity in polar microdomains, which can be explained by the dielectric constant (ε r The frequency (f) dependence of the dielectric constant can be fitted into ε r ~ln(f), the slope of the straight line reflects the consistency (coherence) of the response of the polarization intensity of the polar micro-region to the change of the external electric field. The larger the slope, the more heterogeneous the polarity of the micro-region is, and vice versa, the more homogeneous the polarity of the micro-region is. Figure 3 As shown in (b), in comparison, the trend of the room temperature piezoelectric coefficient of NBBT10 sample under the three cooling rates is that the SC sample shows an increase, followed by NS and QS.

[0053] Embodiment 5: (Na 0.5 Bi 0.5) 0.85 Ba 0.15 TiO 3 , abbreviated as: NBBT15 ceramic

[0054] The NBBT15 ceramic sample was prepared by the traditional solid phase synthesis method. 0.5 Bi 0.5 ) 0.85 Ba 0.15 TiO 3 ) in the metering ratio of adding Bi 2 O 3 , Na 2 CO 3 , BaCO 3 , TiO 2 (Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder of NBBT15. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the weight of the powder binder (5% concentration of polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep warm at 1100℃-1220℃ for 2 hours for sintering, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0055] For the samples with rapid cooling, the samples with polished and parallel two end surfaces were heated to 900°C and kept at this temperature for 1 hour, then taken out directly from the furnace and rapidly cooled to room temperature in air. The ceramic samples obtained by this method were recorded as QS samples.

[0056] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0057] For subsequent electrical testing, silver electrodes were prepared on both ends of the QS, SC and NS samples. The ceramics with prepared electrodes were then polarized at 7 kV / mm electric field for 5 min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0058] like Figure 2 As shown in (b), compared with the NS sample, the diffraction peak of the SC sample of NBBT15 shows a phenomenon of significantly weakened tetragonal symmetry (see the diffraction peak near 46°). Figure 3As shown in (a), compared with the QS sample, both the NS and SC samples of NBBT15 show enhanced heterogeneity in polar microdomains, which can be determined by the dielectric constant (ε r The frequency (f) dependence of the dielectric constant can be fitted into ε r ~ln(f), the slope of the straight line reflects the consistency (coherence) of the response of the polarization intensity of the polar micro-region to the change of the external electric field. The larger the slope, the more heterogeneous the polarity of the micro-region is, and vice versa, the more homogeneous the polarity of the micro-region is. Figure 3 As shown in (b), in comparison, the trend of the room temperature piezoelectric coefficient of NBBT15 sample under the three cooling rates is that the SC sample shows an increase, followed by NS and QS.

[0059] Embodiment 6: (Na 0.5 Bi 0.5 ) 0.80 Ba 0.20 TiO 3 , abbreviated as: NBBT20 ceramic

[0060] The NBBT20 ceramic sample was prepared by the conventional solid phase synthesis method. 0.5 Bi 0.5 ) 0.80 Ba 0.20 TiO 3 ) in the metering ratio of adding Bi 2 O 3 , Na 2 CO 3 , BaCO 3 , TiO 2 (Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder of NBBT20. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the weight of the powder binder (5% concentration of polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep warm at 1100℃-1220℃ for 2 hours for sintering, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0061] For the samples with rapid cooling, the samples with polished and parallel two end surfaces were heated to 900°C and kept at this temperature for 1 hour, then taken out directly from the furnace and rapidly cooled to room temperature in air. The ceramic samples obtained by this method were recorded as QS samples.

[0062] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0063] For subsequent electrical testing, silver electrodes were prepared on both ends of the QS, SC and NS samples. The ceramics with prepared electrodes were then polarized at 7 kV / mm electric field for 5 min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0064] like Figure 2 As shown in (b), compared with the NS sample, the diffraction peak of the SC sample of NBBT20 shows a phenomenon of significantly weakened tetragonal symmetry (see the diffraction peak near 46°). Figure 3 As shown in (a), compared with the QS sample, both the NS and SC samples of NBBT20 show enhanced heterogeneity in polar microdomains, which can be explained by the dielectric constant (ε r The frequency (f) dependence of the dielectric constant can be fitted into ε r ~ln(f), the slope of the straight line reflects the consistency (coherence) of the response of the polarization intensity of the polar micro-region to the change of the external electric field. The larger the slope, the more heterogeneous the polarity of the micro-region is, and vice versa, the more homogeneous the polarity of the micro-region is. Figure 3 As shown in (b), in comparison, the trend of the room temperature piezoelectric coefficient of the NBBT20 sample under the three cooling rates is that the SC sample shows an increase, followed by NS and QS.

[0065] Embodiment 7: (Na 0.5 Bi 0.5 ) 0.75 Ba 0.25 TiO 3 , abbreviated as: NBBT25 ceramic

[0066] The NBBT25 ceramic sample was prepared by the traditional solid phase synthesis method. 0.5 Bi 0.5 ) 0.75 Ba 0.25 TiO 3 ) in the metering ratio of adding Bi 2 O 3 , Na 2 CO 3 , BaCO 3 , TiO 2(Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder of NBBT25. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the weight of the powder as a binder (5% polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep warm at 1100℃-1220℃ for 2 hours for sintering, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0067] For the samples with rapid cooling, the samples with polished and parallel two end surfaces were heated to 900°C and kept at this temperature for 1 hour, then taken out directly from the furnace and rapidly cooled to room temperature in air. The ceramic samples obtained by this method were recorded as QS samples.

[0068] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0069] For subsequent electrical testing, silver electrodes were prepared on both ends of the QS, SC and NS samples. The ceramics with prepared electrodes were then polarized at 7 kV / mm electric field for 5 min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0070] like Figure 2 As shown in (b), compared with the NS sample, the diffraction peak of the SC sample of NBBT25 shows a phenomenon of significantly weakened tetragonal symmetry (see the diffraction peak near 46°). Figure 3 As shown in (a), compared with the QS sample, both the NS and SC samples of NBBT25 show enhanced heterogeneity in polar microdomains, which can be determined by the dielectric constant (ε r The frequency (f) dependence of the dielectric constant can be fitted into ε r ~ln(f), the slope of the straight line reflects the consistency (coherence) of the response of the polarization intensity of the polar micro-region to the change of the external electric field. The larger the slope, the more heterogeneous the polarity of the micro-region is, and vice versa, the more homogeneous the polarity of the micro-region is. Figure 3 As shown in (b), in comparison, the trend of the room temperature piezoelectric coefficient of NBBT25 sample under the three cooling rates is that the SC sample shows an increase, followed by NS and QS.

[0071] Example 8: When Sr, Ba, Nb, and V are doped separately (Na 0.5 Bi0.5 ) 0.94 Ba 0.06 TiO 3 Ceramic, abbreviated as: doped NBBT6

[0072] NBBT6 ceramic samples doped with different elements were prepared by conventional solid phase synthesis. 0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 +X, where X is one of Sr, Ba, Nb, or V) in a stoichiometric ratio 2 O 3 , Na 2 CO 3 , BaCO 3 , SrCO 3 , TiO 2 , Nb 2 O 5 , V 2 O 5 (Analytically pure, Sinopharm Group) raw materials, add alcohol and ball mill for 12 hours and then dry, keep warm at 850℃ for 2 hours to synthesize the initial powder of the corresponding components. Then add alcohol to the synthesized powder and ball mill again for 12 hours and dry, add 10% of the powder weight of the binder (5% concentration of polyvinyl alcohol (PVA) aqueous solution), and use a 0.5-inch diameter mold to press it into a green body by uniaxial compression. After burning off the binder in the green body at a high temperature of 800℃, put it in a muffle furnace and keep it at a temperature of 1100℃-1220℃ for 2 hours for sintering, and then cool it to room temperature at a rate of 3℃ per minute. The sintered ceramics must be surface polished to make their two end faces parallel. For samples with slow cooling, the samples with parallel polished end faces are heated to 900℃ and kept warm for 1 hour, and then cooled to room temperature at a rate of 0.1℃ per minute. The ceramic samples obtained by this method are recorded as SC samples.

[0073] In contrast, the samples that were sintered normally without the above-mentioned slow treatment were recorded as NS samples.

[0074] For subsequent electrical testing, silver electrodes were prepared on both ends of the SC and NS samples (a layer of silver paste was coated on each of the two cross sections and then heat treated at 850°C / 30min). The ceramic with the prepared electrodes was then polarized at 7kV / mm for 5min at room temperature using a DC voltage source. The piezoelectric response was tested at room temperature using a ZJ-4AN quasi-static d33 instrument from the Institute of Acoustics, Chinese Academy of Sciences.

[0075] like Figure 4As shown in Figure 1, compared with the NS sample, the diffraction peaks of the SC sample of Sr, Ba, Nb, and V-doped NBBT6 show a significant weakening of tetragonal symmetry (see the diffraction peak near 46°). Figure 5 As shown, the SC sample of Sr, Ba, Nb, and V doped NBBT6 exhibits an increased room temperature piezoelectric coefficient compared to the NS sample.

[0076] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics, characterized in that: By cooling the sintered sodium bismuth titanate-barium titanate piezoelectric ceramics from high temperature to room temperature at an extremely slow rate, the heterogeneity of the polarization intensity (size and direction) between the polar nano-regions in the structure can be improved, and the energy barrier for the polarization intensity turning in the system can be reduced, which is beneficial to the change of the polarization intensity under an external field, thereby achieving the purpose of improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics.

2. The method for improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics according to claim 1, characterized in that: Sodium bismuth titanate-barium titanate ceramics have a perovskite (ABO3) structure. The sintered sodium bismuth titanate-barium titanate piezoelectric ceramics are subjected to subsequent heat treatment, firstly raised to a certain high temperature and then kept warm for a period of time, and then dropped from the high temperature to room temperature at an extremely slow rate, so that the influence of the complexity of the A-site atomic occupancy on the polar region formation process can be fully reflected, the heterogeneity of the polarization intensity (size and direction) between the polar nano-microregions in the structure is improved, the energy barrier of the polarization intensity turning in the system is reduced, which is beneficial to the change of the polarization intensity under the external field, so as to achieve the purpose of improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics.

3. The method for improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics according to claim 1 or 2, characterized in that: The chemical formula of the sodium bismuth titanate-barium titanate ceramic is (Na 0.5 Bi 0.5 ) 1-x Ba x TiO3, x=0.02,0.06,0.08,0.10,0.15,0.20,0.

25.

4. The method for improving the piezoelectric response of sodium bismuth titanate-barium titanate ceramics according to claim 1 or 2, characterized in that: The peak temperature and holding time of the heat treatment are 900-1000°C / 1-3 hours; the heating rate is 3-10°C / min; and the cooling rate is 0.05-0.2°C / min.

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