Rare-earth-doped bismuth calcium niobate piezoelectric ceramic material as well as preparation method and application thereof

Abstract

The invention belongs to the field of piezoelectric ceramics, and relates to a rare earth doped bismuth calcium niobate piezoelectric ceramic material and a preparation method and application thereof. The chemical composition of the rare earth doped bismuth calcium niobate piezoelectric ceramic material is CaBi < 2-x > Sm < x > Nb < 2 > O < 9 >, wherein x is greater than 0 and less than or equal to 0.07, and the Sm element is doped into the bismuth oxide layer (Bi2O2) < 2 + >.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric ceramics, and relates to a rare earth-doped bismuth calcium niobate piezoelectric ceramic material, its preparation method and application, specifically a preparation method that achieves rare earth ion doping into the bismuth oxygen layer through a two-step synthesis. Background Technology

[0002] Piezoelectric materials are functional materials that can achieve electromechanical coupling. By utilizing their positive and negative piezoelectric effects, electrical signals and mechanical signals can be converted into each other.

[0003] Calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is a bilayered compound. Its unique bismuth layered structure gives it an ultra-high Curie temperature of 940℃, making it a potential material for high-temperature applications. However, due to its low piezoelectric activity of only 6.4 pC / N, it is difficult to adapt to the application of sensors in high-temperature, high-frequency environments. CBN piezoelectric ceramics are made from CaCO₃, Bi₂O₃, and Nb₂O₅ as the main raw materials, sintered at temperatures above 1100℃. Bi₂O₃ is an essential component for the layered structure of CBN ceramics. Because its raw materials contain Bi₂O₃, it is stable at room temperature. However, under high-temperature sintering conditions, bismuth oxide reaches its thermodynamic decomposition temperature and forms gaseous bismuth oxide, thereby creating vacancies in the main phase and reducing the density of the ceramic. The specific formation process is as follows:

[0004] To address the issue of low piezoelectric coefficients, researchers have made significant strides, achieving superior piezoelectric properties. For example, the piezoelectric coefficient of Na / Ce doping at the A-site reaches 16.1 pC / N, W / Cr doping at the B-site reaches 15 pC / N, and Ce / Cr doping at the A / B-site reaches 17 pC / N. These advancements attribute the improved piezoelectric performance to intrinsic contributions—the distortion of the perovskite layer oxygen octahedron [NbO6]—and the influence of both intrinsic and extra-intrinsic contributions. Currently, doping modification of CBN is not limited to the A / B site; introducing Ce into the bismuth oxide layer and Mo into the B-site simultaneously improves piezoelectric performance (d33 = 19 pC / N) and ferroelectric performance (Ps = 14.3 μC / cm²). 2 The efficiency was improved. However, due to its low melting point (817℃), the volatilization of Bi2O3 during sintering is unavoidable. During high-temperature sintering, some Bi2O3 easily volatilizes, leading to a decrease in ceramic density and a deterioration in structural uniformity. Few researchers have addressed the Bi2O3 volatilization problem by adjusting raw materials and processes in CBN piezoelectric systems. Therefore, exploring process improvement methods to solve the Bi2O3 volatilization problem is a crucial challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] To reduce the volatilization of Bi2O3 during sintering due to its low melting point and poor piezoelectric properties, this invention provides a rare-earth-doped bismuth-calcium niobate piezoelectric ceramic material, its preparation method, and its application.

[0006] In a first aspect, the present invention provides a rare-earth-doped bismuth-calcium niobate piezoelectric ceramic material, wherein the chemical composition of the rare-earth-doped bismuth-calcium niobate piezoelectric ceramic material is CaBi. 2-x Sm x Nb₂O₉; where 0 < x ≤ 0.07, and Sm element is doped into the bismuth-oxygen layer (Bi₂O₂). 2+ .

[0007] Ideally, 0.01 ≤ x ≤ 0.07.

[0008] Preferably, the rare earth-doped bismuth calcium niobate piezoelectric ceramic material has a piezoelectric coefficient of at least 13.5 pC / N at room temperature, and more preferably 13.8 to 14.5 pC / N; The Curie temperature of the rare earth-doped bismuth niobate calcium piezoelectric ceramic material is >900℃. The rare-earth-doped bismuth-calcium niobate piezoelectric ceramic material has a resistivity ≤10 at 350℃. 8 Ω·cm.

[0009] Secondly, the present invention provides a method for preparing rare earth-doped bismuth niobate calcium piezoelectric ceramic materials, comprising: (1) The Bi source and Sm source were weighed and mixed according to the molar ratio (2-x):x, and then synthesized to obtain BS powder; (2) The BS powder, Ca source and Nb source are prepared according to the chemical composition CaBi 2-x Sm x Nb2O9 was weighed and mixed, and then pre-calcined to obtain CBSN powder; (3) After the obtained CBSN powder is made into a ceramic blank, it is sintered to obtain the rare earth-doped bismuth calcium niobate piezoelectric ceramic material.

[0010] Preferably, in step (1): the Bi source is at least one of Bi2O3 powder and Bi2O5 powder; the Sm source is at least one of Sm2O3 powder and SmO powder; The synthesis temperature is 400–700℃; the holding time during synthesis is 1–4 hours; the particle size of the BS powder is 1 μm–5 μm. Preferably, after synthesis, the material is further crushed and sieved; Preferably, the heating rate of the synthesis is ≤2℃ / min.

[0011] Preferably, in step (2): the Ca source is at least one of CaCO3 powder and Ca(OH)2; the Nb source is at least one of Nb2O5 powder, NbO2 and Nb2O3; and the particle size of the CBSN powder is 0.6 μm to 5.2 μm. The pre-firing temperature is 700–900°C; the pre-firing time is 1–4 hours; preferably, the pre-firing heating rate is ≤2°C / min. Preferably, after pre-calcination, the material is then crushed and sieved; Preferably, the BS powder, Ca source, and Nb source are mixed and pressed into shape before pre-calcination.

[0012] Preferably, in step (3): the method for preparing the ceramic body includes: first mixing and granulating CBSN powder and binder, then aging and sieving to obtain granulated powder; then pressing the obtained granulated powder into shape, and then extruding it to obtain the ceramic body.

[0013] Furthermore, preferably, the binder is a polyvinyl alcohol aqueous solution with a mass concentration of 5-7 wt%; the amount of polyvinyl alcohol added to the binder is 4-8 wt% of the total mass of the CBSN powder; The aging process involves leaving the room at room temperature for no more than 24 hours. The pressing pressure is 100-200 MPa; The temperature of the plastic discharge is 700-800℃; the plastic discharge time is ≤3 hours; preferably, the heating rate of the plastic discharge is ≤2℃ / min.

[0014] Preferably, in step (3): the sintering temperature is 1100-1200℃; the sintering time is 1-3 hours; preferably, the sintering heating rate is ≤3℃ / minute.

[0015] Preferably, after preparing electrodes on the surface of the obtained rare earth-doped bismuth calcium niobate piezoelectric ceramic material, it is then subjected to polarization treatment. The electrode is a platinum electrode; the preparation method of the platinum electrode includes: a firing temperature of 800-900℃; a holding time of ≤60 minutes; and a heating rate of ≤2℃ / min. The parameters of the polarization treatment include: the polarization field strength is 14-18 kV / mm; the polarization temperature is 160-200℃; and the polarization time is 10-20 minutes.

[0016] Thirdly, the present invention provides an application of rare earth-doped bismuth calcium niobate piezoelectric ceramic material in high-temperature fields.

[0017] The beneficial effects of this invention are: (1) In this invention, by pre-synthesizing Bi2O3 and Sm2O3, while maintaining the high Curie temperature of bismuth calcium niobate, rare earth ion doping of CBN piezoelectric ceramics in the bismuth oxide layer is realized, and its piezoelectric properties are significantly improved. The research results are expected to provide experimental basis for the improvement of CBN piezoelectric ceramic sintering process. (2) Unlike samples prepared by traditional batching methods, this invention utilizes Bi2O3 and Sm2O3 raw materials for pre-synthesis to achieve doping of rare earth element Sm in the bismuth oxide layer. (3) Compared with the undoped ceramic sample, the present invention uses Sm 3+ Replace Bi 3+ It can significantly reduce resistivity while improving the piezoelectric properties of bismuth calcium niobate piezoelectric ceramics. Attached Figure Description

[0018] Figure 1 This invention provides a two-step synthesis of CaBi. 1.95 Sm 0.05 The reaction flow diagram of Nb2O9, where A, B, C, and D represent CaCO3, Bi2O3, Nb2O5, and Sm2O3, respectively; Figure 2 The X-ray diffraction patterns of Bi2O3 and Sm2O3 of this invention are shown in BS-500. Figure 3 This invention provides two-step and one-step synthesis methods for CaBi using different synthetic routes. 1.95 Sm 0.05 X-ray diffraction pattern of Nb2O9; Figure 4 For two-step synthesis (b) and one-step synthesis (a) of CaBi 1.95 Sm 0.05 Raman plot of Nb2O9; Figure 5 For two-step synthesis (b) and one-step synthesis (a) of CaBi 1.95 Sm 0.05 Scanning electron microscope image of the surface of Nb2O9; Figure 6 For two-step synthesis (b) and one-step synthesis (a) of CaBi 1.95 Sm 0.05 AC impedance diagram of Nb2O9; Figure 7 For the two-step (TSS) and one-step (DS) synthesis of CaBi 1.95 Sm 0.05 DC resistance diagram of Nb2O9. Detailed Implementation

[0019] The present invention is further illustrated below through the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the invention. It should be noted that the modified methods designed in this invention are not limited to these specific embodiments. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the present invention, without departing from the spirit and essence of the invention, are also within the scope of protection claimed by this invention. Unless otherwise specified, each percentage refers to a mass percentage.

[0020] Samples prepared using existing conventional batching methods are suitable for A / B site doping of structurally stable bismuth layered ceramics, achieving (Bi2O2). 2+ Doping is not suitable, therefore this invention proposes a two-step synthesis process to not only solve the problem of bismuth oxide volatilization during sintering, but also to enhance piezoelectric properties by incorporating Sm doping into the bismuth oxide layer and altering the surrounding environment of [NbO6]. The two-step synthesis process involves premixing and pre-firing the initial raw materials to form a single-phase solid solution, which is then mixed with the remaining raw materials, synthesized, and sintered. Sm doping is incorporated into (Bi2O2). 2+ The layer changed (Bi2O2). 2+ The environment of the layer affects the atomic shifts in the Nb-O octahedron and contributes to the polarization intensity, thus improving the piezoelectric properties. Therefore, this invention is for the design of (Bi2O2). 2+ A new strategy for doping is proposed.

[0021] Specifically, the rare-earth-doped calcium bismuth niobate piezoelectric ceramic of the present invention has the chemical composition CaBi. 2-x Sm x Nb₂O₉; where 0 < x ≤ 0.07. x is controlled below 0.07 by adjusting Sm. 3+ The substitution amount can control the grain size to obtain piezoelectric ceramic materials with high voltage electrical properties; if the value of x is greater than 0.07, the material properties will decrease significantly, which contradicts the purpose of this invention to improve ceramic properties. In this invention, the Nb-O octahedrons in the perovskite block and (Bi2O2) 2+ The layers are closely related; therefore, (Bi2O2) 2+ Changes in the layer environment affect the environment of the Nb-O octahedron. This invention, Sm... 3+ Replace Bi 3+ By inducing atomic shifts, the lattice structure is significantly affected, thereby increasing the intrinsic contribution to piezoelectric properties and thus obtaining excellent piezoelectric performance.

[0022] In this invention, the preparation process of rare-earth-doped bismuth-calcium niobate piezoelectric ceramics with high piezoelectric properties includes processes such as batching, mixing, synthesis, pre-firing, and sintering. The following exemplarily illustrates the preparation method of rare-earth-doped bismuth-calcium niobate piezoelectric ceramics with high piezoelectric properties provided by this invention.

[0023] Synthesize BS powder. Select raw materials Bi2O3 powder and Sm2O3 powder, weigh and mix them according to (1-x)Bi2O3-xSm2O3 (0<x≤0.07), and then synthesize to obtain BS powder. Use BS powder to replace the corresponding Bi2O3 and Sm2O3 in the traditional sintering method formula. The mixing method can be ball milling. As an example of ball milling, the following steps are taken: wet planetary ball milling is performed on the weighed Bi2O3 and Sm2O3 raw materials according to the stoichiometric ratio, wherein the ratio of raw material powder: anhydrous ethanol: ball milling media is 1:0.5~0.9:1.2~1.8, the mixing time is 2~6 hours, and the ball milling media is agate balls. The ball-milled mixture is dried in a constant temperature oven at 50~100℃.

[0024] In an optional embodiment, the synthesis conditions are as follows: heating to 400–700°C (e.g., 500°C, 600°C, 700°C, etc.) at a heating rate not exceeding 2°C / min, holding at this temperature for 1–4 hours, and then cooling to room temperature in the furnace. If the synthesis temperature is too low, the synthesis temperature for Sm to enter Bi2O3 will not be reached. If the synthesis temperature is too high, an unknown two-phase structure will appear, which is not conducive to the subsequent synthesis of the CBSN main phase. Preferably, the synthesized BS powder is finely ground. During fine grinding, the mass ratio of BS 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. After fine grinding, it is dried in a constant temperature oven at 50–100°C.

[0025] BS powder, CaCO3 powder, and Nb2O5 powder are mixed and pre-fired to obtain CBSN ceramic powder. The mixing method can be ball milling. As an example of ball milling, the following steps are performed: Weighed CaCO3 and Nb2O5 raw materials according to the stoichiometric ratio are mixed with pre-synthesized BS raw material using a wet planetary ball mill. The ratio of raw material powder: anhydrous ethanol: milling media is 1:0.5–0.9:1.2–1.8, the mixing time is 2–6 hours, and the milling media are agate balls. The ball-milled mixture is then dried in a constant temperature oven at 50–100°C.

[0026] In an optional embodiment, the pre-firing conditions are as follows: heating to 700–900°C (e.g., 700°C, 800°C, 900°C, etc.) at a heating rate not exceeding 2°C / min, holding at this temperature for 1–4 hours, and then cooling to room temperature with the furnace. Preferably, the synthesized CBSN ceramic powder is finely ground. During fine grinding, 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. After fine grinding, it is dried in a constant temperature oven at 50–100°C.

[0027] In an optional embodiment, CBSN ceramic powder is granulated with a binder, then aged, pressed, and desizing to obtain a ceramic green body. The amount of binder added is 4-8 wt% of the ceramic powder; preferably, the binder is polyvinyl alcohol. The desizing 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 in the furnace. 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.

[0028] Rare earth-doped bismuth calcium niobate piezoelectric ceramics are obtained by sintering CBSN ceramic powder or ceramic green bodies. Specifically, the plasticized ceramic green body is placed in a five-sided heating furnace. To reduce the volatilization of bismuth oxide at high temperatures, synthesized CBSN ceramic powder is used as a filler, and sintering is performed to obtain bismuth calcium titanate piezoelectric ceramic sheets. 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.

[0029] Rare-earth-doped bismuth-calcium titanate piezoelectric ceramics (processed to the required size if necessary) are coated with platinum, dried, and calcined for curing, and finally polarized. In an optional embodiment, the calcination conditions are: heating to 800–900°C at a heating rate not exceeding 2°C / min, holding at that temperature for no more than 60 minutes, and then cooling to room temperature in the furnace. The polarization conditions are: polarizing at 14–16 kV / mm at 160–200°C for 10–20 minutes. The platinum coating process includes surface cleaning, screen printing of platinum paste, and drying.

[0030] Performance testing: The polarized bismuth-calcium titanate piezoelectric ceramics were tested: the Curie temperature Tc was measured according to GB / T 3389.3; the phase structure of the bismuth-calcium titanate piezoelectric ceramics 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; and 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.

[0031] 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.

[0032] Example 1 In this embodiment 1, a two-step synthesis process is used to prepare CaBi. 1.95 Sm 0.05 Nb2O9 piezoelectric ceramic material, including the following steps: (1) using Bi2O3 powder and Sm2O3 powder as raw materials, according to CaBi 1.95 Sm 0.05 The composition of Nb₂O₉ was designed and the batching calculations were performed. Then, the raw material powder was sequentially placed into a ball mill jar for ball milling and mixing. The ratio of raw material powder, anhydrous ethanol, and milling media (agate balls) was 1:0.65:1.5. The mixture was wet-milled using a planetary ball mill for 4 hours to ensure homogeneity. The mixed raw material powder was then dried at 80℃. The dried raw material powder was passed through a 40-mesh sieve. The powder passed through the 40-mesh sieve was then pressed into blocks using a press. The resulting blocks were placed in an alumina crucible and heated to 500℃ in a high-temperature furnace at a heating rate of 2℃ / min, and held at that temperature for 2 hours. Finally, the furnace was cooled to obtain the desired BS ceramic blocks. (2) The synthesized BS ceramic block was mechanically crushed and passed through a 40-mesh sieve, and then processed according to the CaBi... 1.95 Sm 0.05 The composition of Nb2O9 was determined by calculating the proportions of raw materials CaCO3 powder and Nb2O5 powder. CaCO3 powder, Nb2O5 powder, and BS powder were sequentially added to a ball mill jar for ball milling and mixing. The ratio of raw material powder, anhydrous ethanol, and milling media (agate balls) was 1:0.65:1.5. The mixture was wet-milled using a planetary ball mill for 4 hours to ensure homogeneity. The mixed raw material powder was 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 CBSN ceramic blocks. (3) The synthesized CBSN 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 homogeneous for 6 hours at a mass ratio of ceramic powder: anhydrous ethanol: milling media = 1:0.6:1.5. 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, passed through a 40-mesh sieve, and a granular powder with a certain degree of fluidity was obtained. 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 remove excess plastic and obtain the ceramic green body. (4) Place CBSN powder with the same composition as the ceramic body as 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 this temperature for 2 hours and then cool it to room temperature with the furnace to obtain the desired CBSN ceramic material.

[0033] The ceramic sheet obtained in Example 1 was processed to a thickness of 0.5 mm, then ultrasonically cleaned, dried, and coated with platinum on both sides by screen printing. The temperature was then increased to 850 °C at a rate of 2 °C / min and held for 30 minutes to cure the platinum paste. Finally, it was polarized under the following conditions: a 15 kV / mm electric field was applied in silicone oil at 200 °C for 10 minutes to obtain the polarized bismuth calcium niobate piezoelectric ceramic.

[0034] Example 2 The preparation process of CBSN ceramic material in this Example 2 is the same as in Example 1, except that in step (1), the obtained block is placed in an alumina crucible and heated to 600°C in a high-temperature furnace at a heating rate of 2°C / min and held for 2 hours.

[0035] Example 3 The preparation process of CBSN ceramic material in this embodiment 3 is the same as that in embodiment 1, except that in step (1), the obtained block is placed in an alumina crucible and heated to 700°C in a high-temperature furnace at a heating rate of 2°C / min and held for 2 hours.

[0036] Comparative Example 1 In Comparative Example 1, CaBi was prepared using a one-step synthesis process. 1.95 Sm 0.05 Nb2O9 piezoelectric ceramics include the following steps: (1) Using Bi2O3, CaCO3, Nb2O5 and Sm2O3 powders as raw materials, directly according to CaBi1.95 Sm 0.05 The composition of Nb₂O₉ was designed and the raw materials were calculated and then sequentially placed into a ball mill jar for ball milling and mixing. The ratio of raw material powder, anhydrous ethanol, and milling media (agate balls) was 1:0.65:1.5. The mixture was wet-milled using a planetary ball mill for 4 hours to ensure homogeneity. 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 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, passed through a 40-mesh sieve, and a granular powder with a certain degree of fluidity was obtained. Next, the powder was pressed into circular blanks with a diameter of 13 mm using a specific mold in a press. These blanks were then heated to 750°C in a low-temperature furnace at a heating rate of 2°C / min and held for 2 hours to remove excess material and obtain the ceramic blanks. (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 this temperature for 2 hours and then cool it to room temperature with the furnace to obtain the desired CBSN ceramic sheet.

[0037] The CBSN ceramic sheet obtained in Comparative Example 1 was processed to a thickness of 0.5 mm, then ultrasonically cleaned, dried, and coated with platinum on both sides by screen printing. The temperature was then increased to 850 °C at a rate of 2 °C / min and held for 30 minutes to cure the platinum paste. Finally, it was polarized under the following conditions: in silicone oil at 200 °C, an electric field of 15 kV / mm was applied for polarization for 10 minutes to obtain the polarized bismuth calcium niobate piezoelectric ceramic.

[0038] Comparative Example 2 The preparation process of bismuth calcium niobate in Comparative Example 2 is the same as that in Comparative Example 1, except that the raw materials are Bi₂O₃, CaCO₃, and Nb₂O₅, and Sm 3+ The doping content is 0%.

[0039] Figure 1 This invention provides a two-step synthesis of CaBi. 1.95 Sm 0.05The reaction flow diagram of Nb2O9, where A, B, C, and D represent CaCO3, Bi2O3, Nb2O5, and Sm2O3, respectively.

[0040] Figure 2 The image shows the BS-500 X-ray diffraction patterns of Bi₂O₃ and Sm₂O₃ in this invention. From... Figure 1 As can be seen, after calcination of Bi₂O₃ and Sm₂O₃ at 500℃, the expected solid solution product BS-500 powder was successfully synthesized. In the BS-500 powder, Sm₂O₃ is dissolved in Bi₂O₃, forming a single phase without the appearance of a second phase.

[0041] Figure 3 This invention provides two-step and one-step synthesis methods for CaBi using different synthetic routes. 1.95 Sm 0.05 X-ray diffraction pattern of Nb2O9. As can be seen from the figure, the bismuth calcium niobate piezoelectric ceramics prepared by different methods have a typical bismuth layered structure, with the main peak being the (115) peak, which is consistent with the characteristic peak of the m=2 bismuth layered structure; compared with the original CBN sample, the main peak 115 has a different offset angle, and the TSS has a larger offset angle.

[0042] Figure 4 Raman spectra of CBSN synthesized using different processes. The figures show that at 60 cm⁻¹... -1 The peaks on the left and right are related to (Bi2O2). 2+ The vibrational mode of Bi in the DS method shows that the peak position is consistent with that of pure CBN, and there is no shift, indicating that Sm does not enter (Bi2O2) in the DS method. 2+ Layer. TSS at 60cm -1 The blue shift of the Raman peak indicates that the two-step synthesis method successfully achieved the incorporation of rare earth element Sm into (Bi2O2). 2+ layer.

[0043] Figure 5 This invention provides two-step synthesis (b) and one-step synthesis (a) of CaBi using different synthetic routes. 1.95 Sm 0.05 Scanning electron microscope (SEM) image of the Nb₂O₈ surface. The image shows that the grains exhibit a typical lamellar structure of bismuth layers and strong anisotropy. The grain size of the two-step synthesis is relatively smaller, decreasing by 1.74 μm from the 2.28 μm of the one-step synthesis.

[0044] Figure 6 This invention provides two-step synthesis (b) and one-step synthesis (a) of CaBi using different synthetic routes. 1.95 Sm 0.05The AC impedance spectra of Nb₂O₉ show that the semicircle diameter decreases with increasing temperature, indicating that the temperature coefficient of CBSN ceramics is negative. This is consistent with the thermally excited ion conduction mechanism within the grains. Two-step and one-step synthesis exhibit different electrical transport properties. The single semicircles in the two-step impedance spectra can be attributed to their bulk responses, indicating that only particles contribute to the electrical conductivity of the ceramic. The difference of more than two orders of magnitude between grain relaxation time and grain boundary relaxation time is sufficient to distinguish two semicircular arcs, demonstrating that one-step synthesis involves not only grain response but also grain boundary contributions.

[0045] Figure 7 This invention provides two-step (TSS) and one-step (DS) synthetic routes for the synthesis of CaBi. 1.95 Sm 0.05 DC resistance diagram of Nb₂O₉. Due to Sm 3+ (1.24A, 12CN) and Bi 3+ (1.30A, 12CN) have the same charge and similar trivalent ions (Sm 3 + ), capable of replacing Bi at position A 3+ However, equivalent substitution does not significantly affect conductivity. In BLSFs, (Bi₂O₂) 2+ The layer acts as an insulating plate, while the perovskite blocks contribute to piezoelectric and dielectric properties. (Bi2O2) 2+ The layer acts as a barrier to prevent charge transport, and its resistivity is perpendicular to (Bi₂O₂). 2+ The direction of the layer is primary. Due to Sm 3+ Replace (Bi2O2) 2+ Bi layer 3+ Furthermore, altering the environment reduces resistivity. In this invention, the two-step synthesis of bismuth-calcium niobate ceramic resulted in a resistivity reduction of an order of magnitude compared to the pure composition, precisely verifying the successful incorporation of Sm into (Bi₂O₂). 2+ Layers. However, one-step synthesis actually improved the efficiency by an order of magnitude, indirectly proving that this is Sm. 3+ Entering position A to replace Ca 2+ The effects of doping. The main mechanism of resistivity change is explained as follows: In the bismuth layered structure, the bismuth-oxygen layer acts as a shielding layer, hindering the migration of charged ions. If an ion enters the bismuth-oxygen layer and replaces a Bi atom, this shielding effect is weakened, and the resistivity decreases. If Sm ions replace Ca ions at the A site, it is a high-valence ion replacing a low-valence ion, which is called soft doping and will increase the bulk resistivity.

[0046] Table 1: Synthesis temperature x Resistivity (350℃) piezoelectric coefficient at room temperature Curie temperature Example 1 500℃ 0.05 <![CDATA[7.19×10 7 Ohm cm]]> 14.5pC / N 906℃ Example 2 600℃ 0.05 <![CDATA[4.04×10 7 Ohm cm]]> 14.1 pC / N 901℃ Example 3 700℃ 0.05 <![CDATA[2.80×10 7 Ohm cm]]> 13.8pC / N 905℃ Comparative Example 1 - 0.05 <![CDATA[4.00×10 9 Ohm cm]]> 13.2pC / N 918℃ Comparative Example 2 0 <![CDATA[4.45×10 8 Ohm cm]]> 6.8pC / N 930℃ .

Claims

1. A rare earth doped calcium bismuth niobate piezoelectric ceramic material, characterized by, The rare earth-doped calcium bismuth niobate piezoelectric ceramic material has a chemical composition of CaBi 2-x Sm x Nb2O9; wherein 0 2+ Sm element is doped into a bismuth oxygen layer (Bi2O2) 2. The rare earth doped calcium bismuth niobate piezoelectric ceramic material of claim 1, wherein, 0.01≤x≤0.07。 3. The rare earth doped calcium bismuth niobate piezoelectric ceramic material according to claim 1 or 2, characterized in that, The piezoelectric coefficient of the rare earth doped calcium bismuth niobate piezoelectric ceramic material at room temperature is at least 13.5 pC / N, preferably 13.8-14.5 pC / N; The Curie temperature of the rare earth doped calcium bismuth niobate piezoelectric ceramic material is > 900℃; The resistivity of the rare earth doped calcium bismuth niobate piezoelectric ceramic material is ≤10 8 Ω·cm at 350°C.

4. A method of producing the rare earth-doped calcium bismuth niobate piezoelectric ceramic material according to any one of claims 1 to 3, characterized by, Comprising: (1) weighing and mixing Bi source and Sm source according to the molar ratio (2-x):x, and then synthesizing to obtain BS powder; (2) BS powder, Ca source and Nb source are weighed and mixed according to the chemical composition CaBi 2-x Sm x Nb2O9, and then pre-sintering is performed to obtain CBSN powder; (3) after the CBSN powder is made into a ceramic green body, sintering is performed to obtain the rare earth doped calcium bismuth niobate piezoelectric ceramic material.

5. The preparation method according to claim 4, characterized in that, In step (1), the Bi source is at least one of Bi2O3 powder and Bi2O5 powder; and the Sm source is at least one of Sm2O3 powder and SmO powder. The temperature of the synthesis is 400-700℃; the holding time of the synthesis is 1-4 hours; and the particle size of the BS powder is 1-5 μm. Preferably, after the synthesis, crushing and sieving are performed. Preferably, the heating rate of the synthesis is ≤2℃ / min.

6. The preparation method according to claim 4, characterized in that, In step (2), the Ca source is at least one of CaCO3 powder and Ca(OH)2 powder; the Nb source is at least one of Nb2O5 powder, NbO2 powder and Nb2O3 powder; and the particle size of the CBSN powder is 0.6-5.2 μm. The temperature of the pre-sintering is 700-900℃; the time of the pre-sintering is 1-4 hours; and preferably, the heating rate of the pre-sintering is ≤2℃ / min. Preferably, after the pre-sintering, crushing and sieving are performed. Preferably, before the pre-sintering, the BS powder, the Ca source and the Nb source are mixed and then pressed into a shape.

7. The preparation method according to claim 4, characterized in that, In step (3), the preparation method of the ceramic green body comprises: first mixing the CBSN powder and a binder and granulating, then aging and sieving to obtain granulated powder; and then pressing the obtained granulated powder into a shape, and then performing plastic removal to obtain the ceramic green body.

8. The production method according to claim 7, characterized by, The binder is polyvinyl alcohol aqueous solution with a mass concentration of 5-7 wt%; and the addition amount of polyvinyl alcohol in the binder is 4-8 wt% of the total mass of the CBSN powder. The aging is standing at room temperature for no more than 24 hours. The pressure of the pressing into a shape is 100-200 MPa. The temperature of the plastic removal is 700-800℃; the time of the plastic removal is ≤3 hours; and preferably, the heating rate of the plastic removal is ≤2℃ / min.

9. The production method according to any one of claims 4 to 8, characterized by, In step (3), the temperature of the sintering is 1100-1200℃; the time of the sintering is 1-3 hours; and preferably, the heating rate of the sintering is ≤3℃ / min.

10. The production method according to any one of claims 4 to 8, characterized by, After the obtained rare earth doped calcium bismuth niobate piezoelectric ceramic material is prepared with an electrode on the surface, polarization treatment is performed. The electrode is a platinum electrode; and the preparation method of the platinum electrode comprises: a sintering temperature of 800-900℃; a holding time of ≤60 minutes; and a heating rate of ≤2℃ / min. The parameters of the polarization treatment comprise: a field strength of 14-18 kV / mm; a polarization treatment temperature of 160-200℃; and a polarization treatment time of 10-20 minutes.

11. Use of the rare earth doped calcium bismuth niobate piezoelectric ceramic material of any one of claims 1-3 in high temperature applications.

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