Calcium bismuth titanate piezoelectric ceramic with high piezoelectric property and high-temperature resistivity and preparation method of calcium bismuth titanate piezoelectric ceramic

Abstract

The invention relates to a calcium bismuth titanate piezoelectric ceramic with high piezoelectric property and high-temperature resistivity and a preparation method thereof. The chemical composition of the bismuth calcium titanate piezoelectric ceramic is Ca < 1-x > Bi < 4 + x > Ti < 4 > O < 15 >, and x is the mole percent, 0 lt; x is less than or equal to 0.08. By designing the composition of the calcium bismuth titanate, replacing Ca < 2 + > with Bi < 3 + > and utilizing space charge polarization to improve the piezoelectric property, the piezoelectric property and the high-temperature resistivity of the calcium bismuth titanate piezoelectric ceramic are remarkably improved under the condition that the high Curie temperature of the calcium bismuth titanate piezoelectric ceramic is maintained, and the calcium bismuth titanate piezoelectric ceramic with high Curie temperature, high piezoelectric property and high direct-current resistivity is obtained. The requirements of the piezoelectric ceramic material for the high-temperature piezoelectric vibration sensor are met, and the application of the piezoelectric ceramic material in the high-temperature field is promoted.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric ceramics, and relates to a bismuth calcium titanate piezoelectric ceramic with high voltage and high temperature resistivity and its preparation method. Background Technology

[0002] Piezoelectric materials are a crucial class of information-functional materials, utilizing their direct and inverse piezoelectric effects to achieve the interconversion of mechanical vibrations and electrical signals. High-temperature piezoelectric vibration sensors, made using their direct piezoelectric effect, have significant applications in aerospace, nuclear power, military weaponry, energy, and electronics industries. These sensors are characterized by wide bandwidth, broad measurement range, high sensitivity, large temperature range, small size, light weight, and ease of installation. They also exhibit good linearity and accuracy, making them widely used in testing and calibration, mechanical dynamic experiments, environmental simulation experiments, modal analysis, fault diagnosis, and optimization design in aerospace, energy and power, and marine transportation systems. With the development of testing technology and the advancement of testing requirements, vibration sensors are essential for monitoring the vibration of key components in these fields. The operating temperatures in these environments typically reach 480℃ or even higher, placing higher demands on the piezoelectric ceramics, the core component of high-temperature piezoelectric vibration sensors.

[0003] Bismuth calcium titanate is a tetralayered bismuth compound with a unique crystal structure that results in a high Curie temperature of 780°C, making it a potential candidate for high-temperature piezoelectric materials. However, its spontaneous polarization is confined to a two-dimensional plane, making polarization reversal difficult and resulting in very low piezoelectric performance, which limits its application in practical industrial production. Furthermore, the significant decrease in resistivity at high temperatures also restricts its sensitivity, further limiting its applications.

[0004] To address the issue of low piezoelectric performance, researchers have made significant strides in improving piezoelectric properties through ion doping, achieving relatively superior performance. For example, the piezoelectric coefficient of A-site K / Ce doping reaches 17 pC / N; B-site W doping achieves 18 pC / N; and externally doped MnO2 achieves 14 pC / N. These studies all attribute the improved piezoelectric performance of bismuth layered ceramics to intrinsic contributions—lattice distortion—and intrinsic contributions—domain structure changes. However, due to the extremely stable crystal structure of bismuth layered materials, it is difficult to produce large distortions, thus limiting further improvements in piezoelectric performance. Therefore, exploring alternative methods to obtain high piezoelectric performance remains a crucial challenge in this field. Summary of the Invention

[0005] Aiming at the problem of poor piezoelectric properties of calcium bismuth titanate piezoelectric ceramic materials, the present invention provides a calcium bismuth titanate piezoelectric ceramic with high piezoelectric properties and high-temperature resistivity and a preparation method thereof. By designing the composition of calcium bismuth titanate, the piezoelectric properties are improved by using space charge polarization. While maintaining the high Curie temperature of the calcium bismuth titanate piezoelectric ceramic, its piezoelectric properties and high-temperature resistivity are significantly improved, and a calcium bismuth titanate piezoelectric ceramic with a high Curie temperature, high piezoelectric properties and high DC resistivity is obtained to meet the requirements of piezoelectric ceramic materials for high-temperature piezoelectric vibration sensors and promote its application in the high-temperature field.

[0006] On the one hand, the present invention provides a calcium bismuth titanate piezoelectric ceramic with high piezoelectric properties and high-temperature resistivity. The chemical composition of the calcium bismuth titanate piezoelectric ceramic is Ca 1-x Bi 4+x Ti4O 15 , where x is the molar percentage and 0 < x ≤ 0.08; among them, by controlling x below 0.08, the grain size can be controlled by adjusting the substitution amount of Bi 3+ , affecting the space charge polarization, so as to obtain a piezoelectric ceramic material with high piezoelectric properties and high resistivity; if the value of x is greater than 0.08, the space charge polarization effect is weakened, resulting in a significant decline in material performance, which runs counter to the purpose of improving the ceramic performance in the present invention.

[0007] The present invention uses space charge polarization to improve the piezoelectric properties of calcium bismuth titanate piezoelectric ceramics, designs a simple Bi 3+ substituting Ca 2+ to improve the piezoelectric properties of CBT-based high-temperature piezoelectric ceramics. Bi 3+ substituting Ca 2+ can significantly reduce the grain size (the substitution of Bi 3+ hinders the mass transfer during sintering), which will enable more sites for space charge to aggregate, thus facilitating the formation of space charge polarization, which stimulates excellent piezoelectric properties.

[0008] Preferably, the room-temperature piezoelectric coefficient of the calcium bismuth titanate piezoelectric ceramic is 18.2 - 20.3 pC / N, the Curie temperature > 770 °C, and the high-temperature resistivity at 600 °C is 1.6×10 5 - 4×10 5 Ω·cm.

[0009] On the other hand, the present invention provides a preparation method of a calcium bismuth titanate piezoelectric ceramic with high piezoelectric properties and high-temperature resistivity, including: using Bi2O3, CaCO3 and TiO2 as raw materials, according to Ca 1-x Bi 4+x Ti4O 15(0 < x ≤ 0.08) Weigh the above raw material powders in a stoichiometric ratio, and obtain ceramic powders through mixing and synthesis; sinter the obtained ceramic powders to obtain the calcium bismuth titanate piezoelectric ceramic.

[0010] Preferably, the mixing method is wet planetary ball milling, where the raw material powder: absolute ethanol: ball milling medium = 1: 0.5 - 0.9: 1.2 - 1.8, the mixing time is 2 - 6 hours, and the ball milling medium is agate balls.

[0011] Preferably, the synthesis temperature is 700 - 900 °C and the time is 2 - 4 hours; preferably, heat up to 800 - 900 °C at a heating rate not higher than 2 °C / min, hold for 1 - 3 hours, and cool to room temperature with the furnace.

[0012] Preferably, the sintering conditions are: heat up to 850 - 950 °C at a heating rate not higher than 3 °C / min, then heat up to 1100 - 1200 °C at a heating rate not higher than 2 °C / min, hold for 1 - 3 hours and cool to room temperature with the furnace.

[0013] Preferably, the preparation method further includes: finely grinding the synthesized ceramic powders. When finely grinding, the mass ratio of the ceramic powders: absolute ethanol: ball milling medium = 1: 0.5 - 0.9: 1.2 - 1.8, and the fine grinding time is 4 - 8 hours.

[0014] Preferably, the preparation method further includes: adding a binder to granulate the finely ground and dried ceramic powders, pressing and degassing to obtain a ceramic green body, and then sintering the ceramic green body.

[0015] Preferably, the addition amount of the binder is 4 - 8 wt% of the ceramic powders; preferably, the binder is polyvinyl alcohol.

[0016] Preferably, the degassing conditions are: heat up to 700 - 800 °C at a heating rate not higher than 2 °C / min, hold for less than 3 hours, and cool with the furnace.

[0017] Preferably, the preparation method further includes: coating platinum on the calcium bismuth titanate piezoelectric ceramic, drying and platinum firing for curing treatment, and then polarizing.

[0018] Preferably, the platinum firing for curing conditions are: heat up to 800 - 900 °C at a heating rate not higher than 2 °C / min, hold for less than 60 minutes, and cool to room temperature with the furnace; The polarization conditions are: polarize at 14 - 16 kV / mm at 160 - 200 °C for 10 - 20 minutes.

[0019] Beneficial effects: The present invention has the following advantages: (1) Compared with undoped ceramic samples, the present invention uses Bi 3+ Replace Ca 2+ It can significantly improve the piezoelectric properties and high-temperature resistivity of bismuth calcium titanate piezoelectric ceramics. (2) Unlike the traditional method of improving piezoelectric properties by improving crystal structure and domain structure, this invention utilizes space charge polarization to enhance polarization intensity to improve piezoelectric properties, providing a new mechanism for enhancing the piezoelectric properties of bismuth layered piezoelectric ceramics. Attached Figure Description

[0020] Figure 1 (a) is a schematic diagram of charge accumulation in the interface region caused by dielectric constant mismatch; (b) is the charge and potential distribution in the diffused double layer; (c) is the Ca... 1-x Bi 4+x Ti4O 15 Schematic diagram of the polarization enhancement model for ceramics; Figure 2 For Ca 1-x Bi 4+x Ti4O 15 X-ray diffraction pattern of (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15); Figure 3 In the figure, (a)-(g) represent the piezoelectric ceramic Ca, respectively. 1-x Bi 4+x Ti4O 15 Scanning electron microscope images of (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15), and (h) figure is the particle size distribution map; Figure 4 For Ca 1-x Bi 4+x Ti4O 15 Piezoelectric coefficient diagram for (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15); Figure 5 For Ca 1-x Bi 4+x Ti4O 15 Resistivity versus temperature for (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15); Figure 6 For Ca 1-x Bi 4+x Ti4O 15 Dielectric temperature spectrum (1MHz) of (x = 0, 0.02, 0.04, 0.06, 0.08); Figure 7 In the equation (a)-(e), Ca represents... 1-x Bi4+x Ti4O 15 (x = 0, 0.02, 0.04, 0.06, 0.08) Low-frequency dielectric temperature spectra (100 Hz) before and after polarization. Detailed implementation manners

[0021] To further illustrate the content, features and actual effects of the present invention, the present invention will be described in detail below in conjunction with embodiments. It should be noted that the modification methods designed by the present invention are not limited to these specific implementation manners. Without departing from the spirit and connotation of the design of the present invention, equivalent replacements and modifications made by those skilled in the art on the basis of reading the content of the present invention are also within the scope of protection required by the present invention. Unless otherwise specified, each percentage content refers to mass percentage content.

[0022] The existing piezoelectric activity enhancement mechanisms are not very applicable to structurally stable bismuth-layered ceramics. Therefore, the present invention proposes to use the mechanism of space charge polarization to enhance piezoelectric activity. Space charge polarization (also known as interfacial polarization) is a common microscopic polarization mechanism, which is caused by space charges in a non-uniform system. Currently, it is mainly applied to enhancing polarization, increasing breakdown field strength and increasing dielectric constant, etc. In polycrystalline ceramic samples, grains and grain boundaries also have different dielectric constants, resistivity / resistance. In ceramic samples, it usually occurs at grain boundaries, which is caused by the different dielectric constants, resistivity / resistance and thickness of grains and grain boundaries. This difference will cause a large amount of space charges to accumulate and be arranged orderly at the interface under the action of an external electric field, thereby contributing to the polarization intensity and improving piezoelectric properties. Thus, the present invention proposes a new strategy for designing high-performance piezoelectric ceramics.

[0023] Specifically, the chemical composition of the calcium bismuth titanate piezoelectric ceramic described in the present invention is Ca 1-x Bi 4+x Ti4O 15 , where x is the molar percentage and 0 < x ≤ 0.08. The grain size of the calcium bismuth titanate piezoelectric ceramic is 3.3 - 5.75 μm. In the present invention, Bi 3+ substituting Ca 2+ can significantly reduce the grain size, which will enable more sites for space charges to accumulate, thus facilitating the formation of space charge polarization and stimulating excellent piezoelectric properties. That is, space charge polarization will also occur at the interface between grains and grain boundaries, thereby obtaining excellent piezoelectric properties.

[0024] The formation of space charge polarization can be explained by Maxwell-Wagner theory. In polycrystalline ceramic samples, the property mismatch near grains and grain boundaries leads to charge accumulation near the grain boundaries under the influence of an electric field, thus forming an electric double layer. The potential (cation and anion concentrations) in the diffusion layer varies with the distance from the Helmholtz surface, resulting in a potential difference, such as... Figure 1 As shown in (a) and (b), the ordered local potential differences under the influence of an electric field contribute additional polarization intensity to improve piezoelectric properties, such as... Figure 1 As shown in (c). The change of the above potential with distance can be described by the Debye-Hückel equation: ψ(r)=ψ0e -κr (1) In the formula, ψ0 is the electric potential at the Helmholtz surface. κ is a parameter representing the degree of double-layer decay. i It is a valence state, n i (∞) represents the concentration of ion species i, which is located further away from the interface.

[0025] This invention utilizes space charge polarization to enhance local polarization intensity, thereby obtaining a bismuth-calcium titanate piezoelectric ceramic with high piezoelectric properties. This meets the requirements of high-temperature piezoelectric ceramic components for high-temperature piezoelectric ceramic materials, strongly promoting the application of high-temperature piezoelectric ceramic materials in high-temperature fields, and holds promise for applications in high-temperature piezoelectric vibration sensors at 480℃ and above. In some examples, the piezoelectric coefficient of the bismuth-calcium titanate piezoelectric ceramic is 18.2–20.3 pC / N, the Curie temperature is >770℃, and the high-temperature resistivity at 600℃ is 1.6 × 10⁻⁶. 5 ~4×10 5 Ω·cm. This is comparable to undoped bismuth calcium titanate ceramic (piezoelectricity of 15.3 pC / N, Curie temperature of 780℃, and high-temperature resistivity of 2.5 × 10⁻⁶ at 600℃). 4 Compared to (Ω·cm), the overall performance of the material is significantly improved.

[0026] The present invention also provides a preparation process for the above-mentioned bismuth calcium titanate piezoelectric ceramic, which specifically includes processes such as batching, mixing, synthesis, fine grinding, granulation, molding, plasticizing, and sintering.

[0027] The following is an exemplary description of the preparation method of the bismuth calcium titanate piezoelectric ceramic with high voltage performance and high temperature resistivity provided by the present invention.

[0028] According to Ca 1-x Bi 4+x Ti4O 15Weigh Bi2O3, CaCO3 and TiO2 powders with a stoichiometric ratio of (0 < x ≤ 0.08), and obtain ceramic powders through wet planetary ball milling and synthesis.

[0029] In an alternative embodiment, in the wet planetary ball milling process, mix the raw material powders, absolute ethanol, and ball milling medium in a mass ratio of 1:0.5 - 0.9:1.2 - 1.8 for 2 - 6 hours. The ball milling medium is agate balls. Dry the mixed material after ball milling in a constant temperature oven at 50 - 100°C.

[0030] In an alternative embodiment, the synthesis conditions are as follows: perform heat preservation synthesis at 700 - 900°C for 2 - 4 hours. Preferably, raise the temperature to 800 - 900°C at a heating rate not exceeding 2°C / min, keep the temperature for 1 - 3 hours, and then take out the corresponding synthesized product after cooling to room temperature with the furnace.

[0031] Perform secondary planetary ball milling (i.e., fine grinding) and drying on the synthesized product.

[0032] In an alternative embodiment, during fine grinding, perform fine grinding for 4 - 8 hours according to the mass ratio of synthesized product: absolute ethanol: ball milling medium = 1:0.5 - 0.9:1.2 - 1.8. The ball milling medium is agate balls. After secondary planetary ball milling, dry at 50 - 100°C.

[0033] Add a binder to the powders after fine grinding and drying for granulation. After aging, press into shape and raise the temperature to remove the plasticizer to obtain a ceramic green body.

[0034] In an alternative embodiment, the binder is 7wt.% polyvinyl alcohol (PVA); the addition amount of the binder is 4 - 8wt.% of the dried powders.

[0035] The shaping and plasticizer removal conditions are as follows: use a pressure of 100 - 200 Mpa to press the granulated powders into a disc with a diameter of 13 mm and a thickness of 2 mm. Raise the temperature of the pressed disc to 700 - 800°C at a heating rate not exceeding 2°C / min and keep the temperature for less than 3 hours.

[0036] Put the ceramic green body after plasticizer removal into a five-sided heating furnace. At the same time, in order to reduce the volatilization of bismuth oxide at high temperatures, use the synthesized ceramic powders as fillers to sinter and obtain a calcium bismuth titanate piezoelectric ceramic sheet.

[0037] In an alternative embodiment, the sintering conditions are as follows: raise the temperature to 850 - 950°C at a heating rate not exceeding 3°C / min, and then raise the temperature to 1100 - 1200°C at a heating rate not exceeding 2°C / min, keep the temperature for 1 - 3 hours and cool to room temperature with the furnace.

[0038] The calcium bismuth titanate piezoelectric ceramic sheet is processed into the required size, cleaned, screen-printed with platinum paste, dried, platinum fired, and then electrodes are applied and polarized to obtain the calcium bismuth titanate piezoelectric ceramic.

[0039] In an optional embodiment, the conditions for platinum firing are: heating to 800 - 900 °C at a heating rate not higher than 2 °C / min and holding for less than 60 minutes. The polarization conditions are polarization at 14 - 16 kV / mm at 160 - 200 °C for 10 - 20 minutes.

[0040] The following further gives examples to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can select within a suitable range through the description in this article, rather than being limited to the specific values in the following examples.

[0041] Example 1

[0042] In this Example 1, the solid-phase sintering method is used to prepare Ca 1-x Bi 4+x Ti4O 15 (0 < x ≤ 0.08) piezoelectric ceramics, where x is 0.02: (1) Using Bi2O3, CaCO3 and TiO2 powders as raw materials, formulating and calculating according to the composition design of Ca 1-x Bi 4+x Ti4O 15 , then sequentially putting the raw materials into a ball mill tank for ball milling and mixing. Among them, the ratio of raw material powder, absolute ethanol, and ball milling medium (agate balls) is 1:0.65:1.5, and wet milling is carried out using a planetary ball mill for 4 hours to make it evenly mixed. After drying the mixed raw materials at 80 °C, passing through a 40-mesh sieve, pressing them into a block using a press, and then putting them into an alumina crucible, heating to 850 °C at a heating rate of 2 °C / min in a high-temperature furnace and holding for 2 hours, and cooling with the furnace to obtain the ceramic block required for synthesis; (2) The synthesized ceramic blocks were mechanically crushed and passed through a 40-mesh sieve, and then finely ground using a wet planetary ball mill. The mixture was kept for 6 hours at a mass ratio of ceramic powder: anhydrous ethanol: milling media = 1:0.6:1.5 to ensure uniform mixing. Then, 6 wt.% binder was added to the finely ground powder, and the mixture was granulated. The binder was a 7 wt.% PVA aqueous solution. The granulated powder was pressed into large blocks and allowed to stand for 24 hours for aging. After aging, the powder was crushed and ground in a mortar, then passed through a 40-mesh sieve to obtain a granular powder with a certain degree of fluidity. Next, the powder was pressed into a circular green body with a diameter of 13 mm using a specific mold in a press. Then, the green body was heated to 750°C in a low-temperature furnace at a heating rate of 2°C / min and held for 2 hours to obtain a raw green body. (3) Place the powder with the same composition as the ceramic body as the filler in a sealed alumina crucible (the ceramic body is above the filler), and then place it in a high-temperature furnace and heat it to 900°C at a heating rate of 3°C / min, and then heat it to 1150°C at a heating rate of 2°C / min. Hold it at the temperature for 2 hours and then cool it to room temperature with the furnace to obtain the desired ceramic sheet. (4) The obtained ceramic sheet is processed to a thickness of 0.5 mm, then ultrasonically cleaned, dried, and wire-screened with platinum on both sides. Then, the temperature is raised to 850°C at a rate of 2°C / min and held for 30 minutes to solidify the platinum paste. Finally, polarization is performed. The polarization conditions are: apply a 15 kV / mm electric field to silicone oil at 200°C for 10 minutes to obtain the bismuth calcium titanate piezoelectric ceramic.

[0043] Example 2

[0044] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Example 2 is the same as in Example 1, except that x = 0.04.

[0045] Example 3

[0046] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Example 3 is the same as in Example 1, except that x = 0.06.

[0047] Example 4

[0048] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Example 4 is the same as in Example 1, except that x = 0.08.

[0049] Comparative Example 1

[0050] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Comparative Example 1 is the same as in Example 1, except that x = 0.

[0051] Comparative Example 2

[0052] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Comparative Example 2 is the same as that in Example 1, except that x = 0.1.

[0053] Comparative Example 3

[0054] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Comparative Example 3 is the same as that in Example 1, except that x = 0.15.

[0055] The polarized bismuth-calcium titanate piezoelectric ceramic was tested: Curie temperature T c Tests were conducted according to GB / T 3389.3; the phase structure of the bismuth calcium titanate piezoelectric ceramic was analyzed using an Aeris X-ray diffractometer from PANalyical; and a ZJ-3A quasi-static d-type X-ray diffractometer from the Institute of Acoustics, Chinese Academy of Sciences was used. 33 The tester measures the d of piezoelectric ceramics at room temperature. 33 The test frequency was 100Hz. The microstructure of the bismuth calcium titanate piezoelectric ceramic was analyzed using a Hitachi TM3000 scanning electron microscope. The DC resistivity of the ceramic was measured using a HRMS-1000I high-temperature resistance testing system developed by Bailibo, connected to a Keithley 6517B electrometer / high resistance meter. The test results of various properties of the bismuth calcium titanate piezoelectric ceramic of this invention are shown in Table 1.

[0056] Table 1. Performance test table of bismuth calcium titanate piezoelectric ceramic material.

[0057] As shown in Table 1, the Curie temperature remains essentially constant as x increases, while the piezoelectric coefficient increases significantly, reaching a maximum of 19.8 pC / N in Example 3. Simultaneously, the high-temperature resistivity at 600°C also increases by an order of magnitude, reaching 1.7 × 10⁻⁶ in Example 3. 5 Ω·cm.

[0058] Figure 2 For the present invention Ca 1-x Bi 4+x Ti4O 15 X-ray diffraction pattern of (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15). From Figure 2 As can be seen from the data, the bismuth calcium titanate piezoelectric ceramic prepared by this method has a typical bismuth layered structure, with the main peak being the (119) peak, which is consistent with the characteristic peak of a four-layer bismuth layered structure.

[0059] Figure 3 (ag) is the Ca of this invention 1-x Bi 4+x Ti4O 15Surface scanning electron microscope (SEM) images of particles (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15), with (h) showing the particle size distribution. From... Figure 3 As can be seen from (ag), the grains exhibit a typical lamellar structure of bismuth layers, and the grains possess strong anisotropy. From Figure 3 As can be seen in (h), the grain size shows a decreasing trend as expected, decreasing from 5.75 μm when x = 0.00 to 2.8 μm when x = 0.15, which is conducive to the enhancement of space charge polarization effect.

[0060] Figure 4 For the present invention Ca 1-x Bi 4+x Ti4O 15 Piezoelectric coefficient diagram for (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15). From Figure 4 As can be seen from the figure, the piezoelectric coefficient exhibits a trend of first increasing and then decreasing with the increase of x. In the x = 0.06 composition, the highest piezoelectric coefficient reaches 19.8 pC / N, which is 30% higher than that of the undoped sample. The figure also shows that the piezoelectric coefficient increases and then decreases with increasing doping content, which may be due to the synergistic effect of space charge concentration and grain size. When x ≤ 0.06, the grain size decreases rapidly with increasing x, leading to an increase in grain boundary content. This shortens the migration path of space charge and provides more sites for aggregation to form polarization. In this case, the positive effect of grain size outweighs the negative effect of decreasing space charge concentration, thus improving piezoelectric performance. When x > 0.06, the decreasing trend of grain size slows down with increasing x. In this case, the positive effect of grain size is less than the negative effect of decreasing space charge concentration, thus decreasing piezoelectric performance. It is this synergistic effect that causes the trend of the piezoelectric coefficient first increasing and then decreasing.

[0061] Figure 5 For the present invention Ca 1-x Bi 4+x Ti4O 15 Resistivity versus temperature for (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15). Figure 5 As can be seen, the DC resistivity is significantly improved after doping, increasing by about one order of magnitude at 600℃. This is likely due to the fact that Bi... 3+ Replace Ca 2+ This reduces the carrier concentration, thereby increasing the resistivity.

[0062] Figure 6 For the present invention Ca 1-x Bi 4+x Ti4O 15Dielectric temperature spectrum (1 MHz) of (x = 0, 0.02, 0.04, 0.06, 0.08). From Figure 6 As can be seen, as x increases, the Curie temperature remains basically unchanged, always maintaining a high Curie temperature above 775℃.

[0063] Figure 7 (ae) represents the Ca of this invention. 1-x Bi 4+x Ti4O 15 Low-frequency dielectric temperature spectra (100Hz) before and after polarization (x = 0, 0.02, 0.04, 0.06, 0.08). Space charge polarization at high frequencies (>10). 4 The response to the electric field is small at low frequencies (100 Hz), and it only contributes a large amount to the dielectric constant at low frequencies. Therefore, the strength of space charge polarization of each component can be verified by comparing the dielectric temperature spectra before and after polarization at low frequencies (100 Hz). Figure 7 As shown in (ae), it can be seen that Bi 3+ Replace Ca 2+ The space charge polarization is significantly enhanced, contributing more to the dielectric constant. This directional polarization will intrinsically affect the polarization intensity, thereby significantly improving the piezoelectric properties.

Claims

1. A bismuth-calcium titanate piezoelectric ceramic with high voltage and high temperature resistivity, characterized in that, The chemical composition of the bismuth calcium titanate piezoelectric ceramic is Ca. 1-x Bi 4+x Ti4O 15 Where x is the mole percentage, 0 <x≤0.08。 2. The bismuth calcium titanate piezoelectric ceramic according to claim 1, characterized in that, The bismuth-calcium titanate piezoelectric ceramic has a room temperature piezoelectric coefficient of 18.2–20.3 pC / N, a Curie temperature >770℃, and a high-temperature resistivity of 1.6 × 10⁻⁶ at 600℃. 5 ~4×10 5 Ω·cm.

3. A method for preparing bismuth calcium titanate piezoelectric ceramic according to claim 1 or 2, characterized in that, include: Using Bi2O3, CaCO3 and TiO2 as raw materials, according to the stoichiometric ratio of Ca 1-x Bi 4+x Ti4O 15 (0 < x ≤ 0.08), weigh the above raw material powders, and obtain ceramic powders through mixing and synthesis; sinter the obtained ceramic powders to obtain the calcium bismuth titanate piezoelectric ceramics.

4. The preparation method according to claim 3, characterized in that, The mixing method is wet planetary ball milling, wherein the ratio of raw material powder: anhydrous ethanol: milling media = 1:0.5~0.9:1.2~1.8, the mixing time is 2~6 hours, and the milling media is agate balls.

5. The preparation method according to claim 3 or 4, characterized in that, The synthesis temperature is 700-900℃ and the time is 2-4 hours; preferably, the temperature is increased to 800-900℃ at a heating rate not exceeding 2℃ / min, held for 1-3 hours, and then cooled to room temperature in the furnace.

6. The preparation method according to any one of claims 3-5, characterized in that, The sintering conditions are as follows: heat to 850-950°C at a heating rate not exceeding 3°C / min, then heat to 1100-1200°C at a heating rate not exceeding 2°C / min, hold at that temperature for 1-3 hours, and then cool to room temperature with the furnace.

7. The preparation method according to any one of claims 3-6, characterized in that, The preparation method also includes: fine grinding of the synthesized ceramic powder, wherein the mass ratio of ceramic powder: anhydrous ethanol: milling media is 1:0.5-0.9:1.2-1.8, and the fine grinding time is 4-8 hours.

8. The preparation method according to any one of claims 3-7, characterized in that, The finely ground and dried ceramic powder is granulated by adding a binder, pressed into shape and plasticized to obtain a ceramic green body, and then the ceramic green body is sintered. The amount of binder added is 4-8 wt% of the ceramic powder; preferably, the binder is polyvinyl alcohol.

9. The preparation method according to any one of claims 3-8, characterized in that, The preparation method further includes: the descaling conditions are: heating to 700-800°C at a heating rate not exceeding 2°C / min, holding at that temperature for less than 3 hours, and then cooling with the furnace.

10. The preparation method according to any one of claims 3-9, characterized in that, The preparation method further includes: coating the calcium bismuth titanate piezoelectric ceramic with platinum, drying and calcining it to solidify it, and then polarizing it; The conditions for platinum curing are as follows: heating to 800-900°C at a heating rate not exceeding 2°C / min and holding at that temperature for no more than 60 minutes, and then cooling to room temperature in the furnace. The polarization conditions are: polarization at 14-16 kV / mm and 160-200 °C for 10-20 minutes.

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