Calcium bismuth titanate piezoelectric ceramic with high piezoelectric constant and piezoelectric voltage constant and preparation method thereof

Abstract

The invention relates to a calcium bismuth titanate piezoelectric ceramic with a high piezoelectric constant and a piezoelectric voltage constant and a preparation method of the calcium bismuth titanate piezoelectric ceramic. The chemical composition of the bismuth calcium titanate piezoelectric ceramic is Ca < 0.94 > Bi < 4.06 > Ti < 4 > O < 15-x > wt% MgO, x represents the mass percent of MgO in a Ca < 0.94 > Bi < 4.06 > Ti < 4 > O < 15 > matrix, and x is greater than 0 and less than or equal to 0.3. The Ca0. 94Bi4. 06Ti4O15 component with good piezoelectric property is taken as a matrix, and MgO with low dielectric constant is added, so that the dielectric constant of the calcium bismuth titanate-based high-temperature piezoelectric ceramic is regulated and controlled; meanwhile, a built-in electric field can be established when the free moving charges are polarized, so that the polarization intensity is enhanced, and the piezoelectric property is improved.

Description

Technical Field

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

[0002] As an emerging industry, microelectronics is experiencing exponential growth in demand due to the continuous decline in the power consumption of electronic devices and the rapid development of the Internet of Things (IoT) and wireless sensing technologies. This translates to a need for a large and continuous power supply. However, current energy supply for microelectronics primarily relies on chemical batteries, which have limited lifespans, cause environmental pollution, and are unsuitable for use in harsh environments (i.e., high temperatures), thus restricting their further development. Therefore, there is an urgent need for a simple, long-lasting, safe, and clean energy supply method.

[0003] Mechanical energy, including human movement, machine vibrations, sound waves, and ocean wave energy, is ubiquitous, inexhaustible, and holds promise as one of the energy sources for large-scale development and application. Piezoelectric energy harvesting technology possesses advantages such as simple structure, stable output, sufficient power density, and good integration with microelectromechanical systems (MEMS), making it highly promising for replacing traditional battery systems and achieving energy self-sufficiency. Piezoelectric materials can directly convert mechanical energy into high-power-density electrical energy and are considered candidates for energy harvesting applications.

[0004] Calcium bismuth titanate (CaBi4Ti4O) 15 Bismuth ether is a tetralayered bismuth compound. Its unique crystal structure results in a high Curie temperature of 780°C, making it a promising candidate for energy harvesting in high-temperature environments. However, its spontaneous polarization is confined to a two-dimensional plane, making polarization reversal difficult and resulting in very low piezoelectric properties. Furthermore, its relatively high dielectric constant further limits its operating voltage output (high voltage output depends on the piezoelectric voltage constant g). 33 , and g 33 Proportional to the piezoelectric constant d 33 The voltage output is inversely proportional to the relative permittivity ε. Current research in this field largely focuses on improving piezoelectric properties, with almost no work addressing increasing voltage output by reducing the permittivity. For example, Li / Ce doping at the A-site increases the piezoelectric coefficient to 20 pC / N, and Nb / Mn doping at the B-site increases it to 23 pC / N. However, the relative permittivity in these studies generally remains around 150, and mostly shows an increasing trend with increasing doping content, which is detrimental to improving voltage output. Therefore, finding a high-temperature piezoelectric ceramic that simultaneously possesses a high permittivity and a piezoelectric voltage constant is an urgent problem to be solved. Summary of the Invention

[0005] To address the issue of low piezoelectric constant and piezoelectric voltage constant in bismuth calcium titanate piezoelectric ceramic materials, this invention provides a bismuth calcium titanate composition design that simultaneously possesses high piezoelectric constant and piezoelectric voltage constant, in order to meet the needs of energy harvesting applications in high-temperature environments.

[0006] On one hand, the present invention provides a bismuth calcium titanate piezoelectric ceramic having a high piezoelectric constant and a piezoelectric voltage constant, wherein the chemical composition of the bismuth calcium titanate piezoelectric ceramic is Ca. 0.94 Bi 4.06 Ti4O 15 -x wt%MgO, where x represents the percentage of MgO in Ca. 0.94 Bi 4.06 Ti4O 15 The mass percentage of the matrix is ​​0 < x ≤ 0.3. By controlling x below 0.3, the structure and properties of the ceramic can be controlled simply by adjusting the MgO content, thus meeting the requirements of piezoelectric energy harvesters for piezoelectric ceramic materials (high voltage constant, high voltage voltage constant). If the value of x is greater than 0.3, the added MgO may enter the crystal lattice, causing a significant deterioration in the performance of the piezoelectric ceramic material, which contradicts the purpose of this invention to improve the performance of piezoelectric ceramics.

[0007] The calcium bismuth titanate piezoelectric ceramic with high piezoelectric constant and piezoelectric voltage constant in this invention is based on Ca with good piezoelectric properties. 0.94 Bi 4.06 Ti4O 15 The matrix is ​​composed of MgO, which has a low dielectric constant. This allows for the modulation of the dielectric constant of bismuth calcium titanate-based high-temperature piezoelectric ceramics. The added MgO component, with its freely moving charges, can also establish a built-in electric field during polarization, thereby increasing the piezoelectric constant. In existing technologies, improvements in piezoelectric performance are generally attributed to lattice distortion and domain structure changes caused by ion doping. However, this invention does not utilize ion doping to improve piezoelectric performance. Instead, it avoids the reaction between MgO and the matrix, utilizing the semiconductor properties of MgO itself to enhance piezoelectric performance. MgO exists independently as a single phase at the grain boundaries. Due to its low dielectric constant, it can reduce the dielectric constant of bismuth calcium titanate ceramics, while its semiconductor properties ensure the formation of a built-in electric field, thereby enhancing polarization intensity and improving piezoelectric performance.

[0008] Preferably, MgO and Ca 0.94 Bi 4.06 Ti4O 15 The matrix does not react but exists independently as a separate second phase at the grain boundaries.

[0009] Preferably, the bismuth-calcium titanate piezoelectric ceramic having a high piezoelectric constant and a piezoelectric voltage constant has a room temperature piezoelectric coefficient of 25.1–28.7 pC / N, a relative permittivity of 70–101, and a piezoelectric voltage constant of 30 × 10⁻⁶. -3 ~50×10 -3 Vm / N.

[0010] On the other hand, the present invention also provides a method for preparing the above-mentioned bismuth-calcium titanate piezoelectric ceramic with high piezoelectric constant and piezoelectric voltage constant, the preparation method comprising: pretreating MgO powder at 1450-1550℃ for 1-3 hours; and pretreating Ca... 0.94 Bi 4.06 Ti4O 15 The bismuth-calcium titanate piezoelectric ceramic is obtained by mixing bismuth-calcium titanate piezoelectric powder with pretreated MgO powder at high temperature according to the stoichiometric ratio of bismuth-calcium titanate piezoelectric ceramic. The purpose of pretreating the MgO powder at high temperature is to reduce its reactivity through high-temperature sintering, thereby preventing it from reacting with the bismuth-calcium titanate matrix. Without pretreatment, MgO has high reactivity and can undergo ion exchange with the matrix, preventing MgO from existing independently at grain boundaries and weakening its influence on the piezoelectric properties and dielectric constant of the piezoelectric ceramic.

[0011] Preferably, the preparation method includes: using Bi2O3, CaCO3 and TiO2 as raw materials, according to Ca... 0.94 Bi 4.06 Ti4O 15 The above raw material powders were weighed according to stoichiometry, and Ca was obtained through mixing and synthesis. 0.94 Bi 4.06 Ti4O 15 Powder; Ca 0.94 Bi 4.06 Ti4O 15 The powder and the MgO powder after high-temperature pretreatment were mixed according to the stoichiometric ratio of bismuth calcium titanate piezoelectric ceramic and sintered to obtain the bismuth calcium titanate piezoelectric ceramic.

[0012] Preferably, the Ca is prepared 0.94 Bi 4.06 Ti4O 15 The powder is mixed using wet planetary ball milling, with a ratio of raw material powder: anhydrous ethanol: milling media of 1:0.5-0.9:1.2-1.8, and a mixing time of 2-6 hours.

[0013] Preferably, the Ca 0.94 Bi 4.06 Ti4O 15The synthesis temperature of the powder is 700-900℃, and the time is 2-4 hours; preferably, the temperature is raised 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.

[0014] Preferably, the high-temperature pretreatment process of the MgO powder includes: heating the MgO powder to 1450-1550°C at a heating rate not exceeding 2°C / min, and holding it at that temperature for 1-3 hours.

[0015] Preferably, Ca 0.94 Bi 4.06 Ti4O 15 The powder and the MgO powder after high-temperature pretreatment are mixed by fine grinding. During fine grinding, the mass ratio of powder: anhydrous ethanol: ball milling media is 1:0.5~0.9:1.2~1.8, and the fine grinding time is 4~8 hours.

[0016] Preferably, the sintering conditions are as follows: heating to 850-950°C at a heating rate not exceeding 3°C / min, then heating to 1100-1200°C at a heating rate not exceeding 2°C / min, holding at that temperature for 1-3 hours, and then cooling to room temperature in the furnace.

[0017] Preferably, the preparation method further includes: adding a binder to finely ground and dried ceramic powder to granulate, pressing and molding to obtain a ceramic green body, and then sintering the ceramic green body.

[0018] Preferably, the amount of the binder added is 4 to 8 wt% of the ceramic powder; more preferably, the binder is polyvinyl alcohol.

[0019] Preferably, the conditions for descaling 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.

[0020] Preferably, the preparation method further includes: coating the bismuth calcium titanate piezoelectric ceramic with platinum, drying and calcining it to cure it, and then polarizing it.

[0021] Preferably, the conditions for the platinum curing are: 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.

[0022] Beneficial effects

[0023] The present invention has the following advantages: (1) Compared with ceramic samples without MgO modification, the present invention significantly improves the piezoelectric constant and piezoelectric voltage constant of bismuth calcium titanate piezoelectric ceramics by adding MgO. (2) The present invention reduces the reactivity of MgO powder with the matrix by high-temperature pretreatment, thereby improving the electrical performance of piezoelectric ceramics by utilizing the semiconductor properties of MgO itself. Attached Figure Description

[0024] Figure 1 For Ca 0.94 Bi 4.06 Ti4O 15 X-ray diffraction patterns of MgO (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, x = 0.2 untreated) at wt%. Figure 2 For Ca 0.94 Bi 4.06 Ti4O 15 -0.2wt% MgO (a) High-temperature pretreatment (b) Scanning electron microscopy and EDS images of untreated MgO; Figure 3 For Ca 0.94 Bi 4.06 Ti4O 15 Piezoelectric coefficient diagram of -x wt% MgO (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, x = 0.2 untreated); Figure 4 For Ca 0.94 Bi 4.06 Ti4O 15 Piezoelectric voltage constant plot of -x wt% MgO (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, x = 0.2 untreated). Detailed Implementation

[0025] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention, without departing from its spirit and essence, are also within the scope of protection claimed by the invention. Unless otherwise specified, percentage content refers to mass percentage content.

[0026] Existing piezoelectric ceramic materials cannot simultaneously meet the requirements of high-temperature energy harvesters in terms of both piezoelectric coefficient and dielectric constant. To address this, this invention proposes an innovative compositional design. By adding MgO, the relative dielectric constant of bismuth calcium titanate-based ceramics is effectively reduced (increasing the piezoelectric voltage constant) while maintaining the high piezoelectric coefficient, providing a new approach for the application of bismuth calcium titanate-based ceramics in high-temperature piezoelectric energy harvesters. Specifically, this invention provides a doped and modified bismuth calcium titanate-based ceramic with a composition of Ca... 0.94 Bi 4.06 Ti4O 15 -x wt%MgO, where 0 < x ≤ 0.3.

[0027] MgO is a typical wide-bandgap semiconductor oxide with a low relative permittivity (~10) and semiconductor properties. Therefore, the addition of low-permittivity magnesium oxide can reduce the relative permittivity of bismuth calcium titanate-based ceramics, thereby increasing the piezoelectric voltage constant. The semiconductor properties also cause local field (directional polarization) charges to be generated in MgO, which is beneficial to improving the piezoelectric coefficient.

[0028] This invention successfully improved the piezoelectric constant and piezoelectric voltage constant of bismuth calcium titanate-based ceramics using the above-mentioned components. Utilizing the low dielectric constant and semiconductor properties of magnesium oxide, the dielectric constant of bismuth calcium titanate-based ceramics was successfully reduced, and the local polarization intensity was increased by establishing a built-in electric field, thereby obtaining bismuth calcium titanate piezoelectric ceramics with high piezoelectric performance. This meets the requirements of piezoelectric ceramics for piezoelectric energy harvesting devices in high-temperature environments, strongly promoting the application of high-temperature piezoelectric ceramic materials in high-temperature fields, and is expected to be applied to high-temperature piezoelectric energy harvesters at 500℃ and above. In some examples, the piezoelectric coefficient of the bismuth calcium titanate piezoelectric ceramic is 25.1–28.7 pC / N (preferably 25.4–28.3 pC / N), the Curie temperature is >775℃, the relative permittivity is 70–101 (preferably 70–96), and the piezoelectric voltage constant is 30 × 10⁻⁶. -3 ~50×10 -3 Vm / N (preferably 32.8 × 10⁻⁶) -3 ~48.6×10 -3 Vm / N).

[0029] 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.

[0030] The following is an exemplary description of the preparation method of the bismuth calcium titanate piezoelectric ceramic provided by the present invention.

[0031] According to Ca 0.94 Bi 4.06 Ti4O 15Bi₂O₃, CaCO₃, and TiO₂ powders were weighed according to their stoichiometric ratios, and then synthesized by wet planetary ball milling to obtain Ca. 0.94 Bi 4.06 Ti4O 15 Powder.

[0032] In an optional embodiment, the wet planetary ball mill is used to mix materials at a mass ratio of raw material: anhydrous ethanol: milling media = 1:0.5-0.9:1.2-1.8 for 2-6 hours, using agate balls as the milling media. The milled mixture is then dried in a constant temperature oven at 50-100°C.

[0033] In an optional embodiment, the synthesis conditions are as follows: synthesis at 700–900°C for 2–4 hours. Preferably, the temperature is increased to 800–900°C at a heating rate not exceeding 2°C / min, held for 1–3 hours, and then cooled to room temperature in the furnace to obtain the corresponding synthesized product.

[0034] Ca 0.94 Bi 4.06 Ti4O 15 The powder and the MgO powder after high-temperature pretreatment were subjected to secondary planetary ball milling (i.e. fine grinding) and drying according to the stoichiometric ratio of bismuth calcium titanate piezoelectric ceramic.

[0035] In an optional embodiment, the high-temperature pretreatment process of the MgO powder includes: heating the MgO powder to 1450-1550°C at a heating rate not exceeding 2°C / min, and holding it at that temperature for 1-3 hours.

[0036] In an optional embodiment, the secondary planetary ball milling is performed for 4-8 hours at a mass ratio of powder: anhydrous ethanol: milling media = 1:0.5-0.9:1.2-1.8. The milling media are agate balls. After the secondary planetary ball milling, the mixture is dried at 50-100°C.

[0037] A binder is added to the finely ground and dried powder for granulation. After aging, the powder is pressed into shape and heated to remove plastic, thus obtaining a ceramic body.

[0038] In an optional embodiment, the binder is 7 wt.% polyvinyl alcohol (PVA); the amount of binder added is 4-8 wt.% of the dried powder.

[0039] The molding and desizing conditions are as follows: the granulated powder is pressed into discs with a diameter of 13 mm and a thickness of 2 mm using a pressure of 100-200 MPa. The pressed discs are then heated to 700-800 °C at a heating rate not exceeding 2 °C / min and held at that temperature for no more than 3 hours.

[0040] The ceramic blank after desizing was placed in a five-sided heating furnace. Meanwhile, in order to reduce the volatilization of bismuth oxide at high temperature, the synthesized ceramic powder was used as a filler and sintered to obtain bismuth calcium titanate piezoelectric ceramic sheets.

[0041] In an optional embodiment, the sintering conditions are as follows: heating to 850-950°C at a heating rate not exceeding 3°C / min, then heating to 1100-1200°C at a heating rate not exceeding 2°C / min, holding at that temperature for 1-3 hours, and then cooling to room temperature in the furnace.

[0042] The bismuth calcium titanate piezoelectric ceramic sheet is processed to the required size, cleaned, screen-printed with platinum paste, dried, calcined, and then electrodes are applied and polarized to obtain the bismuth calcium titanate-based piezoelectric ceramic material.

[0043] In an optional embodiment, the conditions for platinum calcination are: 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.

[0044] The polarization conditions are: polarization at 14–16 kV / mm and 160–200 °C for 10–20 minutes.

[0045] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0046] Example 1

[0047] In this embodiment 1, Ca was prepared using a solid-state sintering method. 0.94 Bi 4.06 Ti4O 15 –0.1wt% MgO piezoelectric ceramics: (1) Using Bi2O3, CaCO3, and TiO2 powders as raw materials, according to Ca 0.94 Bi 4.06 Ti4O 15The composition design was used to calculate the ingredients, and then the raw materials were sequentially placed into a ball mill jar for ball milling and mixing. The ratio of powder raw materials, anhydrous ethanol, and ball milling media (agate balls) was 1:0.65:1.5. The mixture was wet-milled for 4 hours using a planetary ball mill to ensure uniform mixing. The mixed raw materials were dried at 80℃, passed through a 40-mesh sieve, and pressed into blocks using a press. These blocks were then placed in an alumina crucible and heated to 850℃ in a high-temperature furnace at a rate of 2℃ / min, held at that temperature for 2 hours, and then cooled in the furnace to obtain the desired ceramic blocks. (2) The MgO powder was heated to 1550℃ at a heating rate of 2℃ / min and held for 2 hours to obtain MgO powder after high-temperature pretreatment. The obtained ceramic blocks were mechanically crushed and passed through a 40-mesh sieve. The MgO powder after high-temperature pretreatment was weighed according to the mass ratio and mixed and finely ground together with the above ceramic powder. The mixture was kept at a mass ratio of powder: anhydrous ethanol: ball milling media = 1:0.6:1.5 for 6 hours to ensure uniform mixing. Then, 6 wt.% of binder (7 wt.% PVA by mass) was added to the finely ground powder and granulated. 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 and passed through a 40-mesh sieve to obtain a granular powder with a certain degree of flowability. Next, the powder is pressed into a circular blank with a diameter of 13mm in a press using a specific mold. Then, it is heated to 750℃ in a low-temperature furnace at a heating rate of 2℃ / min and held for 2 hours to remove plastic and obtain a raw blank. (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 then platinum is brushed on both sides of the screen. The temperature is then increased 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.

[0048] Example 2

[0049] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Example 2 is the same as in Example 1, except that x = 0.2.

[0050] Example 3

[0051] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Example 3 is the same as in Example 1, except that x = 0.3.

[0052] Comparative Example 1

[0053] 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.

[0054] Comparative Example 2

[0055] 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 = 0.4.

[0056] Comparative Example 3

[0057] 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 = 0.5.

[0058] Comparative Example 4

[0059] The preparation process of the bismuth calcium titanate piezoelectric ceramic in Comparative Example 4 is the same as that in Example 2, except that MgO was not pretreated at high temperature.

[0060] 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 capacitance C of the bismuth calcium titanate piezoelectric ceramic was measured using a Keysight 4990A precision impedance analyzer, and the relative permittivity was calculated; based on the piezoelectric coefficient d... 33 Calculate the piezoelectric voltage coefficient g using the relative permittivity. 33 The test results of various properties of the bismuth calcium titanate piezoelectric ceramic of the present invention are shown in Table 1.

[0061] Table 1. Performance test table of bismuth calcium titanate piezoelectric ceramic material.

[0062] As shown in Table 1, the Curie temperature remains constant with increasing MgO doping content, while the piezoelectric coefficient and piezoelectric voltage coefficient both show a trend of first increasing and then decreasing, reaching a maximum of 28.3 pC / N and 48.6 × 10⁻⁶ pC / N, respectively. -3The Vm / N ratio indicates excellent overall performance. However, without pretreatment of MgO, both the piezoelectric coefficient and piezoelectric voltage coefficient exhibit low values, even inferior to the electrical performance without MgO. This is because MgO, without high-temperature treatment, has high reactivity and can undergo ion exchange with the bismuth calcium titanate matrix. 2+ This will replace Ti in the bismuth calcium titanate matrix. 4+ This acceptor doping prevents the voltage from being applied properly during polarization, and MgO can no longer provide a built-in electric field, thus leading to a decrease in electrical performance.

[0063] Table 1 also shows that, compared to Comparative Example 1 without pretreated magnesium oxide, the relative permittivity of the bismuth calcium titanate piezoelectric ceramics obtained in Examples 1-3 and Comparative Examples 2-3 after adding pretreated magnesium oxide decreased. However, compared to Comparative Example 4 with untreated magnesium oxide, the relative permittivity actually increased. This is because when untreated magnesium oxide is added, its breakdown field strength is low, preventing normal polarization (normal polarization voltage is 16 kV / mm, while it is only 10 kV / mm), thus increasing the relative permittivity.

[0064] Figure 1 For the present invention Ca 0.94 Bi 4.06 Ti4O 15 X-ray diffraction patterns of 10-x wt% MgO (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, x = 0.2 untreated). From Figure 1 As can be seen from the XRD pattern, the bismuth calcium titanate-based piezoelectric ceramic prepared by this method exhibits a typical bismuth layered structure, with the main peak being the (119) peak, which conforms to the characteristic peaks of a four-layer bismuth layered structure. The XRD image also shows that when x ≤ 0.2, the (119) peak does not show a significant shift, while when x > 0.2 or when untreated magnesium oxide is added, the (119) peak shifts significantly to the left. This is precisely due to the large radius Mg... 2+ Replace small radius Ti 4+ The resulting peak shift.

[0065] Figure 2 For the present invention Ca 0.94 Bi 4.06 Ti4O 15 -0.2wt% MgO (a) High-temperature pretreated (b) Scanning electron microscopy and EDS images of untreated MgO. From Figure 2As can be seen from the data, the reactivity of MgO added after high-temperature pretreatment in the sample of Example 2 decreased, and it ultimately existed as a second phase (MgO) at the grain boundaries. EDS analysis showed the aggregation of Mg and O elements. In contrast, no second phase was found at the grain boundaries in the sample of Comparative Example 4, where untreated MgO was added, indicating that MgO did not exist as a second phase. No element aggregation was observed in the EDS image, suggesting that MgO aggregation may have occurred. 2+ Replace Ti 4+ .

[0066] Figure 3 For Ca 0.94 Bi 4.06 Ti4O 15 The piezoelectric coefficient graph for -x wt% MgO (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, x = 0.2 untreated) shows that the piezoelectric coefficient initially increases and then decreases, reaching a maximum of 28.3 pC / N. This increase in piezoelectric coefficient is likely due to the semiconductor properties of magnesium oxide; the internal polarization charges generate a localized field that enhances polarization, thereby increasing the piezoelectric coefficient.

[0067] Figure 4 For Ca 0.94 Bi 4.06 Ti4O 15 The piezoelectric voltage constant of MgO (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, x = 0.2 untreated) is plotted. The plot shows that the piezoelectric voltage constant first increases and then decreases with increasing MgO content. This is because when the MgO content is low, the low dielectric constant and semiconductor properties of MgO can improve the piezoelectric voltage constant of bismuth calcium titanate piezoelectric ceramics. However, with increasing MgO content, even with high-temperature pretreatment to reduce reactivity, the presence of excessive MgO undoubtedly increases the reaction probability, thus weakening its contribution to the dielectric constant and piezoelectric properties.

Claims

1. A bismuth-calcium titanate piezoelectric ceramic having both a high piezoelectric constant and a piezoelectric voltage constant, characterized in that, The chemical composition of the bismuth calcium titanate piezoelectric ceramic is Ca. 0.94 Bi 4.06 Ti4O 15 -x wt%MgO, where x represents the percentage of MgO in Ca. 0.94 Bi 4.06 Ti4O 15 The mass percentage of the matrix, 0 < x ≤ 0.

3.

2. The bismuth calcium titanate piezoelectric ceramic according to claim 1, characterized in that, MgO and Ca 0.94 Bi 4.06 Ti4O 15 The matrix does not react but exists independently as a separate second phase at the grain boundaries.

3. The bismuth calcium titanate piezoelectric ceramic according to claim 1 or 2, characterized in that, The bismuth-calcium titanate piezoelectric ceramic with high piezoelectric constant and piezoelectric voltage constant has a room temperature piezoelectric coefficient of 25.1–28.7 pC / N, a relative permittivity of 70–101, and a piezoelectric voltage constant of 30 × 10⁻⁶. -3 ~50×10 -3 Vm / N.

4. A method for preparing a bismuth calcium titanate piezoelectric ceramic having a high piezoelectric constant and a piezoelectric voltage constant according to claim 1 or 2, characterized in that, include: MgO powder was pretreated at 1450–1550℃ for 1–3 hours; Ca… 0.94 Bi 4.06 Ti4O 15 The powder and the MgO powder after high-temperature pretreatment were mixed according to the stoichiometric ratio of bismuth calcium titanate piezoelectric ceramic and sintered to obtain the bismuth calcium titanate piezoelectric ceramic.

5. The preparation method according to claim 4, characterized in that, The preparation method includes: using Bi₂O₃, CaCO₃, and TiO₂ as raw materials, according to Ca... 0.94 Bi 4.06 Ti4O 15 The above raw material powders were weighed according to stoichiometry, and Ca was obtained through mixing and synthesis. 0.94 Bi 4.06 Ti4O 15 Powder; Ca 0.94 Bi 4.06 Ti4O 15 The powder and the MgO powder after high-temperature pretreatment were mixed according to the stoichiometric ratio of bismuth calcium titanate piezoelectric ceramic and sintered to obtain the bismuth calcium titanate piezoelectric ceramic.

6. The preparation method according to claim 4 or 5, characterized in that, Preparation of the Ca 0.94 Bi 4.06 Ti4O 15 The powder is mixed using a wet planetary ball mill, with the ratio of raw material powder: anhydrous ethanol: milling media = 1:0.5~0.9:1.2~1.8, and the mixing time is 2~6 hours. The Ca 0.94 Bi 4.06 Ti4O 15 The synthesis temperature of the powder is 700-900℃, and the time is 2-4 hours; preferably, the temperature is raised 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.

7. The preparation method according to any one of claims 4-6, characterized in that, Ca 0.94 Bi 4.06 Ti4O 15 The powder and the MgO powder after high-temperature pretreatment are mixed by fine grinding. During fine grinding, the mass ratio of powder: anhydrous ethanol: ball 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 4-7, 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.

9. The preparation method according to any one of claims 4-8, characterized in that, The preparation method also includes: adding a binder to finely ground and dried ceramic powder to granulate, pressing and molding to obtain a ceramic green body, and then sintering the ceramic green body; The amount of binder added is 4-8 wt% of the ceramic powder; preferably, the binder is polyvinyl alcohol. The conditions for descaling are as follows: 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 4-9, 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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