Doped and modified bismuth calcium niobate-based ceramic material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ceramic material preparation, and particularly relates to a doped and modified bismuth calcium niobate-based ceramic material and a preparation method and application thereof, the chemical general formula of the doped and modified bismuth calcium niobate-based ceramic material is Ca1-X (MaCebNdc) XBi2Nb1. 96W0. 04O9, x is more than or equal to 0.005 and less than or equal to 0.04, M represents an alkali metal element, 0 lt, 0 < = x < = 0, 0 < = y < = 0, 0 < = y < = 0, and 0 < = y < = 0. A + b + clt; 1, and a + 3b + 3clt; and 2, introducing trace vacancies at the site A, preparing CaCO3 powder, Bi2O3 powder, Nb2O5 powder, M2CO3 powder, Ce2O3 powder, Nd2O3 powder and WO3 powder according to a design ratio, carrying out primary ball milling, pre-sintering and secondary ball milling to obtain mixed powder, carrying out pre-pressing molding on the mixed powder, carrying out cold isostatic pressing to obtain a green blank sheet, and sintering the green blank sheet to obtain the bismuth calcium niobate ceramic material. The piezoelectric property of the bismuth calcium niobate ceramic material is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of ceramic material preparation technology, specifically relating to a doped and modified bismuth niobate calcium-based ceramic material, its preparation method, and its application. Background Technology

[0002] As an important functional ceramic material, piezoelectric ceramics work on the principle of energy conversion between electrical and mechanical energy based on the piezoelectric effect. This effect can be used to manufacture piezoelectric sensors, which have many important applications in high-temperature fields. However, due to the Curie temperature of piezoelectric ceramics, there is currently a lack of piezoelectric sensors that can operate stably above 500 ℃.

[0003] However, in specialized fields such as aerospace and oil exploration, the performance requirements for piezoelectric sensors in high-temperature environments are constantly increasing. Currently, there are no qualified high-temperature piezoelectric vibration sensor products in China that can reliably operate above 600 ℃.

[0004] Bismuth-layered piezoelectric ceramics possess characteristics such as high Curie temperature (650–950℃), low dielectric constant, low aging rate, and high resistivity. This makes bismuth-layered piezoelectric ceramics promising for the fabrication of high-temperature piezoelectric sensors. Bismuth-layered piezoelectric ceramics consist of a bismuth oxide layer (Bi₂O₂). 2+ It is composed of alternating layers of α and β-perovskite, and its general chemical formula is (Bi₂O₂). 2+ (A m-1 B m O 3m+1 ) 2 In the formula, A represents a dodecahedral coordination of monovalent, divalent, and trivalent cations or combinations thereof, forming a dodecahedral coordination; B represents a series of transition metal cations satisfying hexacoordination, forming an octahedral coordination; m represents the number of oxygen octahedral layers in the perovskite-like structure, ranging from 1 to 6. Among them, calcium bismuth niobate (CaBi₂Nb₂O₉, m = 2) is a typical bismuth layered piezoelectric ceramic with a Curie temperature reaching 950 ℃, making it one of the bismuth layered piezoelectric ceramics with the highest Curie temperature. It also possesses the characteristics of strong anti-aging ability of BLSFs, making it a highly promising material candidate for high-temperature piezoelectric sensors. Researching its piezoelectricity and thermal stability is of great significance in overcoming foreign restrictions on high-temperature piezoelectric sensors in my country. CBN (calcium bismuth niobate) has good stability and low aging rate, showing great application prospects in the fields of high-temperature sensors and high-temperature high-frequency applications. However, it still has some inherent drawbacks and inherent limitations of BLSFs (bismuth layered ferroelectric ceramics), and its piezoelectric constant d... 33It is very low (6 pC / N) due to its special layered structure, which restricts the direction of spontaneous polarization to the ab plane, making it exceptionally difficult for ferroelectric domains to flip along the c-axis.

[0005] Scholars both domestically and internationally have been dedicated to finding various methods to improve the piezoelectric properties of CBN ceramics. One such method is to prepare textured ceramics through special techniques. CBN ceramic texturing can generally be divided into process improvement and using sintering aids to enhance the degree of texturing. Texturing methods do not significantly reduce the Curie temperature of the ceramic. Two common approaches are employed: one is heat treatment techniques such as plasma sintering (SPS), hot pressing (HP), and hot forging (HT); the other is grain-based micro-orientation growth methods such as template grain growth (TGG) and molten salt (MS). However, these methods involve complex processes and are not suitable for large-scale industrial production.

[0006] The traditional solid-state reaction method using two-step sintering is simple to operate and suitable for large-scale production. Currently, the most widely used method for performance improvement is to enhance the electrical properties of CBN through chemical composition design modification. In the layered structure of CBN bismuth, the A and B sites in its perovskite-like layer can be occupied by a series of equivalent or non-equivalent ions with similar ionic radii. Therefore, the doping modification research of CBN mainly focuses on the A, B sites and AB site composite substitution. Through atomic substitution, the original crystal structure will be distorted to a certain extent, thereby enhancing its spontaneous polarization and improving its piezoelectric properties. Summary of the Invention

[0007] The purpose of this invention is to provide a doped and modified bismuth niobate calcium-based ceramic material, its preparation method and application. It employs equimolar doping of A sites with Li, Ce and Nd, and introduces equimolar vacancies at the A sites. At the same time, it employs W doping of B sites, which significantly improves the piezoelectric properties.

[0008] To achieve the above objectives, the present invention provides a doped and modified calcium bismuth niobate-based ceramic material, wherein the general chemical formula of the calcium bismuth niobate-based ceramic material is: Ca 1-X (M a Ce b Nd c ) X Bi2Nb 1.96 W 0.04 O9, where M represents an alkali metal element, 0.005≤x≤0.04, a+b+c<1, and a+3b+3c<2. The total stoichiometry of M, Ce, and Nd is less than 1, and the sum of their valences is less than the valence of calcium ions (2). Therefore, under ideal stoichiometry, there is a vacancy for the element, forming an A-site Ca ion vacancy.

[0009] Furthermore, M is one of the elements Li, Na, and K, preferably Li, and x represents the molar fractions of the three elements Li, Ce, and Nd. For the calcium bismuth niobate-based ceramic material with the doping amount within this range, not only the high Curie temperature is maintained, but also the piezoelectric properties are significantly improved. Especially when x is 0.02, the piezoelectric properties of the obtained calcium bismuth niobate-based ceramic are more than twice that of the pure calcium bismuth niobate ceramic.

[0010] Furthermore, 0.7 < a + b + c < 1 and 1.6 < a + 3b + 3c < 2.

[0011] Furthermore, 0.05 < a < 0.32, 0.05 < b < 0.32, 0.05 < c < 0.32. Preferably, it also satisfies a = b = c. More preferably, a = b = c = 0.25.

[0012] The present invention also provides a preparation method for the doped and modified calcium bismuth niobate-based ceramic material described in any one of the above, including the following steps:

[0013] S1. Calculate and weigh the raw materials according to the stoichiometric ratio of the elements other than oxygen in the chemical general formula. The raw materials include a Ca source, a Bi source, a Nb source, an M source, a Ce source, a Nd source, and a W source, and all contain oxygen. Then, perform primary wet ball milling and mixing to obtain a primary ball milled material. S2. Dry the primary ball milled material and then pass it through a sieve, and perform pre-sintering to obtain a pre-sintered powder. S3. Perform secondary wet ball milling on the pre-sintered powder to obtain a secondary ball milled material. S4. Dry the secondary ball milled material and then pass it through a sieve. Then, perform pre-pressing and molding and then cold isostatic pressing to obtain a green body. S5. Sinter the green body to obtain a sintered ceramic sheet. S6. Polish both sides of the sintered ceramic sheet and then coat electrodes, and then apply a voltage for polarization to obtain a doped and modified calcium bismuth niobate-based ceramic material.

[0014] Furthermore, in step S1, the raw materials are carbonates or oxides. In particular, the Ca source is CaCO3 powder, the Bi source is Bi2O3 powder, the Nb source is Nb2O5 powder, the M source is the carbonate powder of M (such as Li2CO3 powder), the Ce source is Ce2O3 powder, the Nd source is Nd2O3 powder, and the W source is WO3 powder.

[0015] Furthermore, in step S1, the solvent used in the first wet ball milling is anhydrous ethanol, and the milling medium is zirconia spheres; the mass ratio of zirconia spheres, raw materials, and anhydrous ethanol is 5:(1-3):(3-5), preferably 5:2:4; and / or, the milling time is 12-20 h, and the milling speed is 300-350 r / min, preferably 325 r / min. The first ball milling is to mix the raw materials evenly. The milling time has little impact on its uniformity, but it is still necessary to control the milling speed and milling time to a certain extent to avoid poor uniformity affecting subsequent steps.

[0016] Furthermore, in step S2, the pre-sintering atmosphere is air, the heating rate is 2 ℃ / min, the temperature is 850℃-900 ℃, and the holding time is 2-3h. And / or, in step S5, the sintering atmosphere is air, the temperature is 1120 ℃-1200 ℃, and the holding time is 2-3 hours. Preferably, the temperature is first raised to 900 ℃ at a relatively fast rate, followed by a slower rate to 1150 ℃. The growth of bismuth calcium niobate ceramic grains and the ceramic shrinkage process mainly occur after 1000 ℃. Maintaining a relatively fast heating rate before 900 ℃ can reduce the volatilization of volatile elements to a certain extent without affecting the normal growth process of bismuth calcium niobate ceramics. Reducing the heating rate after 900 ℃ can avoid rapid grain growth, thereby obtaining high-density bismuth calcium niobate-based ceramics. The bismuth calcium niobate-based ceramics sintered under this sintering process have the best performance.

[0017] Further, in step S3, the solvent used in the secondary wet ball milling is anhydrous ethanol, and the milling medium is zirconia spheres; the mass ratio of zirconia spheres, pre-calcined powder, and anhydrous ethanol is 5:(1-3):(3-5), preferably 5:2:4; and / or, the milling time is 12-20 h, and the milling speed is 300-350 r / min, preferably 325 r / min. The purpose of the second ball milling is to obtain the finest possible powder particle size to ensure sufficient reaction between the powders during the formal sintering process; therefore, the second ball milling time should be extended as much as possible. The first and second ball millings utilize a planetary ball mill.

[0018] After the second ball milling, the resulting ball milled material is dried in an oven, ground, and then passed through an 80-mesh sieve. The preferred particle size of the resulting powder is 1-2 μm. In this invention, the particle size of the powder is controlled at 1-2 μm. If the particle size is too large, voids are easily left during pre-pressing and isostatic pressing, making it difficult to obtain high-density ceramics during subsequent sintering. If the second ball milling time is too long or the ball milling speed is too fast, the powder particle size will be too small, resulting in poor flowability, which is not conducive to pre-pressing.

[0019] Furthermore, in step S4, the pre-pressing involves applying a pressure of 0.5-1 MPa for preliminary shaping, resulting in a thickness of 1-2 mm and a diameter of 12 mm. The cold isostatic pressing includes: placing the pre-shaped powder block into a plastic package and vacuuming it, then placing it in an isostatic press and applying pressure at a holding pressure of 180-220 MPa for 4-6 minutes. By precisely controlling the powder particle size and isostatic pressing pressure within the above ranges, the final sintered sample can achieve optimal density and piezoelectric properties.

[0020] Furthermore, in step S6, the polarization includes: placing the sintered ceramic sheet coated with the electrode in silicone oil at 130-170°C, applying a polarization electric field of 15-20 kV / mm, and polarization time of 15-25 min.

[0021] Preferably, the silicone oil temperature is 150°C and the polarization time is 20 min.

[0022] Furthermore, the sintered bismuth calcium niobate-based ceramic material was polished to 0.5 mm, polished on both sides, and then coated with high-temperature silver paste. The silver firing conditions were controlled to be held at 850 ℃ for 15 min.

[0023] The present invention also provides an application of the doped and modified bismuth calcium niobate-based ceramic material described above, or the doped and modified bismuth calcium niobate-based ceramic material obtained by any of the above preparation methods, wherein the doped and modified bismuth calcium niobate-based ceramic material is used in the field of piezoelectric sensors.

[0024] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. The bismuth calcium niobate-based ceramic material provided by the present invention, based on the existing B-site W element doping, adopts equimolar doping of the A-site with Li, Ce and Nd, and introduces an equal amount of vacancies at the A-site. This not only significantly improves the density of the bismuth calcium niobate-based ceramic and enhances the polarization electric field of the bismuth calcium niobate-based ceramic during the polarization process, but also improves the piezoelectric coefficient of the bismuth calcium niobate-based piezoelectric ceramic.

[0025] 2. In this invention, the ion valence state of W element at the B site is +6. By doping with a suitable concentration of high-valence ions, the oxygen vacancy concentration in bismuth calcium niobate is reduced, thereby reducing the conductive holes inside the ceramic and improving the bulk resistivity of the ceramic.

[0026] 3. Due to Li + Ce 3+ and Nd 3+The ions have valences of +1, +3, and +3, respectively. Combined with A-site vacancies, the overall molar average valence of the composite at this ratio is slightly lower than +2, which can balance the B-site doping of +6 W to some extent. Co-doping of low-valence A-sites and high-valence B-sites can balance the overall valence state and fine-tune the oxygen vacancy concentration, thereby enabling bismuth calcium niobate-based ceramics to achieve improved piezoelectric properties while maintaining stable Curie temperatures. Furthermore, because the average ionic radius of the A-site dopant group is similar to that of Ca... 2+ The difference in ionic radii causes lattice distortion, which further separates the positive and negative charge centers, thereby enhancing the piezoelectric properties.

[0027] 4. The element used for the A-site doping group is crucial. If only an alkaline earth metal element is used for A-site doping, while improving piezoelectric performance, it usually significantly reduces the Curie temperature. Co-doping of the A-site with an alkali metal element combined with a rare earth metal element improves piezoelectric performance without significantly reducing the Curie temperature. This is because the 4f electron configuration of the rare earth metal element forms a strong lattice bond, suppressing polarization relaxation at high temperatures. This invention employs co-doping of the A-site with an alkali metal element and a rare earth metal element, further improving the piezoelectric activity and thermal stability of bismuth calcium niobate ceramics.

[0028] 5. Introducing A-site vacancies: A small number of A-site vacancies can not only balance the valence state of doped groups, but also weaken the long-range lattice order, break the strict ab-plane polarization restriction of orthorhombic phases, thereby providing greater flexibility for polarization direction adjustment, reducing the polarization reversal energy barrier, and improving piezoelectric activity.

[0029] 6. The method for preparing the doped and modified bismuth calcium niobate ceramic material of the present invention can be obtained by ordinary ceramic preparation methods, with low preparation cost, simple process and suitability for large-scale industrial production. The piezoelectric properties of the doped and modified bismuth calcium niobate ceramic material are significantly improved compared with those of undoped bismuth calcium niobate ceramics, and its di value is improved while maintaining a high Curie point. 33 This has increased the efficiency by more than two times, advancing the application of high-temperature piezoelectric materials. Attached Figure Description

[0030] Figure 1 These are the X-ray diffraction patterns of bismuth niobate calcium-based ceramics in Examples 1-4 when x = 0.005-0.02.

[0031] Figure 2 These are the X-ray diffraction patterns of bismuth niobate calcium-based ceramics in Examples 5-8 when x = 0.02-0.04.

[0032] Figure 3 This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.005 in Example 1.

[0033] Figure 4This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.01 in Example 2.

[0034] Figure 5 This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.015 in Example 3.

[0035] Figure 6 This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.02 in Example 4.

[0036] Figure 7 This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.025 in Example 5.

[0037] Figure 8 This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.03 in Example 6.

[0038] Figure 9 This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.035 in Example 7.

[0039] Figure 10 This is a SEM image of the bismuth niobate calcium-based ceramic at x=0.04 in Example 8.

[0040] Figure 11 This is a SEM image of the pure bismuth niobate-based ceramic in Comparative Example 1.

[0041] Figure 12 The piezoelectric coefficient d of the bismuth niobate calcium-based ceramic sheet in Comparative Example 1 and Examples 1-5 33 The comparison. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0043] Example 1 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.005 is abbreviated as CBNW-0.5LCN.

[0044] Analytical purity solid raw materials, including 5.043 g CaCO3 powder, 23.6 g Bi2O3 powder, 13.325 g Nb2O5 powder, 0.0023 g Li2CO3 powder, 0.0109 g Ce2O3 powder, 0.0107 g Nd2O3 powder, and 0.2348 g WO3 powder, were weighed and prepared according to the traditional solid-phase reaction process. The raw materials were then mixed at a mass ratio of zirconia spheres, raw materials, and anhydrous ethanol of 5:2:4 (the same applies to the following examples). The mixture was ball-milled at 325 r / min for 12 h, dried through an 80-mesh sieve, and pre-calcined at 875 ℃ in air for 2 h. The pre-calcined powder was then mixed again at a mass ratio of zirconia spheres, powder, and anhydrous ethanol of 5:2:4 (the same applies to the following examples) and ball-milled at 325 r / min for 20 h. After drying and passing through an 80-mesh sieve, the material is pre-pressed and placed in an isostatic press at 200 MPa for 5 minutes to obtain a green compact. The green compact is then sintered in a furnace using a process involving heating to 900 °C at a rate of 3-5 °C / min, followed by heating to 1120-1200 °C at a rate of 2 °C / min, holding for 150 minutes, and finally cooling in the furnace. This yields a doped and modified bismuth-calcium niobate-based lead-free piezoelectric ceramic. The ceramic sample is polished to a thickness of 0.5 mm, coated with a high-temperature silver electrode, and immersed in silicone oil at 150 °C. It is then polarized for 20 minutes under a polarization field of 15-20 kV / mm, and its piezoelectric coefficient d is measured. 33 =11 pC / N.

[0045] Example 2 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.01 is abbreviated as CBNW-1LCN.

[0046] Analytical-grade solid raw materials, including 5.017 g CaCO3 powder, 23.592 g Bi2O3 powder, 13.322 g Nb2O5 powder, 0.0046 g Li2CO3 powder, 0.0218 g Ce2O3 powder, 0.0213 g Nd2O3 powder, and 0.2347 g WO3 powder, were weighed and prepared according to the traditional solid-phase reaction process. The raw materials were then mixed with anhydrous ethanol and ball-milled at 325 r / min for 12 h. After drying and passing through an 80-mesh sieve, the mixture was pre-calcined at 875 ℃ for 2 h. The pre-calcined powder was then ball-milled again at 325 r / min for 20 h, dried, passed through an 80-mesh sieve, and pre-pressed. The resulting powder was then placed in an isostatic press and held at 200 MPa for 5 minutes. After a period of time, a green body was obtained and placed in a furnace for sintering. The sintering process involved heating the green body to 900℃ at a rate of 3-5℃ / min, then heating it to 1120-1200℃ at a rate of 2℃ / min, holding it at that temperature for 150 min, and finally cooling it in the furnace to obtain doped and modified bismuth calcium niobate-based lead-free piezoelectric ceramics. The ceramic sample was polished to a thickness of 0.5 mm, coated with a high-temperature silver electrode, and placed in silicone oil at 150℃. It was then polarized for 20 min under a polarization electric field of 15-20 kV / mm, and its piezoelectric coefficient d was measured. 33 =13 pC / N.

[0047] Example 3 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.015 is abbreviated as CBNW-1.5LCN.

[0048] Analytical purity solid raw materials, including 4.991 g CaCO3 powder, 23.584 g Bi2O3 powder, 13.319 g Nb2O5 powder, 0.00701 g Li2CO3 powder, 0.0327 g Ce2O3 powder, 0.0319 g Nd2O3 powder, and 0.2347 g WO3 powder, were weighed and prepared according to the traditional solid-phase reaction process. The raw materials were then mixed with anhydrous ethanol and ball-milled at 325 r / min for 12 h. After drying and passing through an 80-mesh sieve, the mixture was pre-calcined at 875 ℃ for 2 h. The pre-calcined powder was then ball-milled again at 325 r / min for 20 h, dried, passed through an 80-mesh sieve, and pre-pressed. The resulting powder was then placed in an isostatic press and held at 200 MPa for 5 minutes. After a period of time, a green body was obtained and placed in a furnace for sintering. The sintering process involved heating the green body to 900℃ at a rate of 3-5℃ / min, then heating it to 1120-1200℃ at a rate of 2℃ / min, holding it at that temperature for 150 min, and finally cooling it in the furnace to obtain doped and modified bismuth calcium niobate-based lead-free piezoelectric ceramics. The ceramic sample was polished to a thickness of 0.5 mm, coated with a high-temperature silver electrode, and placed in silicone oil at 150℃. It was then polarized for 20 min under a polarization electric field of 15-20 kV / mm, and its piezoelectric coefficient d was measured. 33 =13.5 pC / N.

[0049] Example 4 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.02, is abbreviated as CBNW-2LCN.

[0050] Analytical-grade solid raw materials, including 4.965 g CaCO3 powder, 23.576 g Bi2O3 powder, 13.316 g Nb2O5 powder, 0.0093 g Li2CO3 powder, 0.0436 g Ce2O3 powder, 0.0426 g Nd2O3 powder, and 0.2346 g WO3 powder, were weighed and prepared according to the traditional solid-phase reaction process. The raw materials were then mixed with anhydrous ethanol and ball-milled at 325 r / min for 12 h. After drying and passing through an 80-mesh sieve, the mixture was pre-calcined at 875 ℃ for 2 h. The pre-calcined powder was then ball-milled again at 325 r / min for 20 h, dried, passed through an 80-mesh sieve, and pre-pressed. The resulting powder was then placed in an isostatic press and held at 200 MPa for 5 minutes. After a period of time, a green body was obtained and placed in a furnace for sintering. The sintering process involved heating the green body to 900℃ at a rate of 3-5℃ / min, then heating it to 1120-1200℃ at a rate of 2℃ / min, holding it at that temperature for 150 min, and finally cooling it in the furnace to obtain doped and modified bismuth calcium niobate-based lead-free piezoelectric ceramics. The ceramic sample was polished to a thickness of 0.5 mm, coated with a high-temperature silver electrode, and placed in silicone oil at 150℃. It was then polarized for 20 min under a polarization electric field of 15-20 kV / mm, and its piezoelectric coefficient d was measured. 33 =15.3 pC / N.

[0051] Example 5 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.025 is abbreviated as CBNW-2.5LCN.

[0052] Other conditions were the same as in Examples 1-4, except that the proportions of raw materials in the batching process were changed. After the resulting ceramic samples were polarized under the same conditions, their piezoelectric coefficient d was tested. 33 =13.7 pC / N.

[0053] Example 6 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 Bismuth calcium niobate ceramics modified with O9 and x=0.03 are abbreviated as CBNW-3LCN.

[0054] Other conditions were the same as in Examples 1-4, except that the proportions of raw materials in the batching process were changed. After the resulting ceramic samples were polarized under the same conditions, their piezoelectric coefficient d was tested. 33 =13.7pC / N.

[0055] Example 7 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 O 99 Bismuth calcium niobate ceramics modified with x=0.035 are referred to as CBNW-3.5LCN.

[0056] Other conditions were the same as in Examples 1-4, except that the proportions of raw materials in the batching process were changed. After the resulting ceramic samples were polarized under the same conditions, their piezoelectric coefficient d was tested. 333 =13.5 pC / N.

[0057] Example 8 Preparation of Ca 1-X (Li 0.25 Ce 0.25 Nd 0.25 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.04 is abbreviated as CBNW-4LCN.

[0058] Other conditions were the same as in Examples 1-4, except that the proportions of raw materials in the batching process were changed. After the resulting ceramic samples were polarized under the same conditions, their piezoelectric coefficient d was tested. 333 =12.3 pC / N.

[0059] Example 9 Preparation of Ca 1-X (Li 0.2 Ce 0.28 Nd 0.28 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.04 is abbreviated as CBNW-4LCN.

[0060] Other conditions were the same as in Examples 1-4, except that the proportion of raw materials in the batching process was changed. After the ceramic samples were polarized under the same conditions, they were tested and found to have a high piezoelectric coefficient.

[0061] Example 10 Preparation of Ca 1-X (Li 0.3 Ce 0.22 Nd 0.22 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.04 is abbreviated as CBNW-4LCN.

[0062] Other conditions were the same as in Examples 1-4, except that the proportion of raw materials in the batching process was changed. After the ceramic samples were polarized under the same conditions, they were tested and found to have a high piezoelectric coefficient.

[0063] Example 11 Preparation of Ca 1-X (Li 0.1 Ce 0.3 Nd 0.3 ) X Bi2Nb 1.96 W 0.04 O9, and the bismuth calcium niobate ceramic modified by doping with x=0.04 is abbreviated as CBNW-4LCN.

[0064] Other conditions were the same as in Examples 1-4, except that the proportion of raw materials in the batching process was changed. After the ceramic samples were polarized under the same conditions, they were tested and found to have a high piezoelectric coefficient.

[0065] Comparative Example 1 Bismuth calcium niobate ceramics conforming to the general chemical formula CaBi2Nb2O9 were prepared, abbreviated as CBN.

[0066] Analytical-grade solid raw materials, 4.1923 g CaCO3 powder, 19.54 g Bi2O3 powder, and 11.1007 g Nb2O5 powder, were prepared according to the traditional solid-phase reaction process. The raw materials were then mixed with anhydrous ethanol and ball-milled at 325 r / min for 12 h. After drying and passing through an 80-mesh sieve, the mixture was pre-calcined at 875 ℃ for 2 h. The pre-calcined powder was then ball-milled again at 325 r / min for 20 h, dried, passed through an 80-mesh sieve, and pre-pressed. The resulting green body was placed in an isostatic press and held at 200 MPa for 5 min to obtain a green body. The green body was then sintered in a furnace using the following process: heating to 900 ℃ at a rate of 3-5 ℃ / min, then heating to 1120-1200 ℃ at a rate of 2 ℃ / min, and holding at that temperature for 150 minutes. After cooling in the furnace for 20 minutes, the doped and modified bismuth calcium niobate-based lead-free piezoelectric ceramic was obtained. The ceramic sample was polished to a thickness of 0.5 mm, a high-temperature silver electrode was coated on the surface, and it was placed in silicone oil at 150°C and polarized for 20 minutes under a polarization electric field of 15-20 kV / mm. Its piezoelectric coefficient d was then measured. 33 ≈6 pC / N.

[0067] Figure 1 and Figure 2 The XRD patterns of bismuth niobate calcium-based ceramics with x = 0.005–0.02 and x = 0.025–0.04 are shown. All diffraction peaks are consistent with the standard card PDF#49-0608, and no impurity phases were found, indicating that no second phase was formed. The shift of the main peak shows that with the increase of doping concentration, all diffraction peaks gradually shift to higher angles. This is also one of the signs that small-sized dopant groups have entered the crystal lattice to form a solid solution. All elements have entered the crystal lattice to form a solid solution, and the space group is A. 21 am.

[0068] Figures 3 to 10 The images show SEM images of bismuth niobate calcium-based ceramics with doping levels of x = 0.005-0.04. Figure 11 The images show SEM images of pure bismuth calcium niobate. Comparison reveals that, firstly, the grain size is significantly reduced after doping, which is beneficial for improving ceramic density. Secondly, pure CBN exhibits the typical plate-like grain morphology of bismuth layered piezoelectric ceramics with obvious anisotropy. After doping, the anisotropy of the ceramic grains is significantly reduced, and the grains tend to grow isotropically. This typically brings two benefits: firstly, isotropically grown ceramic grains are beneficial for improving ceramic density; secondly, isotropically grown grains can weaken the restriction of the layered structure on spontaneous polarization intensity, which is beneficial for improving spontaneous polarization and thus improving the piezoelectric coefficient of the ceramic.

[0069] Figure 12The piezoelectric coefficients of pure bismuth calcium niobate and bismuth calcium niobate-based ceramics with doping amounts of x = 0.005-0.04 were compared. The piezoelectric properties of the bismuth calcium niobate-based ceramics after doping were significantly improved compared to those of pure bismuth calcium niobate. Among them, the ceramic sample with x = 0.02 had the best piezoelectric properties, which were more than twice those of pure bismuth calcium niobate.

[0070] In summary, the piezoelectric properties of the doped and modified bismuth niobate-calcium-based piezoelectric ceramics described in this invention are significantly improved, with the optimal piezoelectric coefficient d0 being achieved. 33 The pC / N ratio is 15.3 (x=0.02), which is much higher than the 6 pC / N ratio of pure bismuth calcium niobate ceramic. The multi-element co-doped modified bismuth calcium niobate ceramic material of this invention is a lead-free piezoelectric ceramic material with a layered structure of bismuth calcium niobate, and its Curie temperature is around 950℃. The piezoelectric properties are... 33 It can reach 15.3 pC / N and has good high-temperature stability. Its piezoelectric properties only depolarize when it reaches the Curie point, and it has good application prospects in high-temperature fields such as aerospace and steelmaking.

[0071] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A doped and modified bismuth niobate calcium-based ceramic material, characterized in that, The chemical general formula of the calcium bismuth niobate-based ceramic material is: Ca 1-X (M a Ce b Nd c ) X Bi2Nb 1.96 W 0.04 O9, where M represents an alkali metal element, 0 < a + b + c < 1, and a + 3b + 3c < 2, 0.005 ≤ x ≤ 0.

04.

2. The doped and modified bismuth niobate calcium-based ceramic material according to claim 1, characterized in that, M is one of the elements Li, Na, and K, 0.7 <a+b+c<1,1.6<a+3b+3c<2。 3. A method for preparing the doped and modified bismuth niobate calcium-based ceramic material according to any one of claims 1-2, characterized in that, Includes the following steps: S1. Calculate and weigh the raw materials according to the stoichiometric ratio of elements other than oxygen in the general chemical formula. The raw materials include Ca source, Bi source, Nb source, M source, Ce source, Nd source and W source, and all contain oxygen. Then, perform a wet ball milling to mix them to obtain a primary ball milling material. S2. After drying the primary ball milling material, sieve it and perform pre-sintering to obtain pre-sintered powder. S3. The pre-calcined powder is subjected to secondary wet ball milling to obtain secondary ball milled material; S4. After drying the secondary ball milling material, sieve it, pre-press it into shape, and then perform cold isostatic pressing to obtain a green body. S5. The green blank is sintered to obtain a sintered ceramic sheet; S6. Polish both sides of the sintered ceramic sheet and coat it with electrodes, then apply voltage to polarize it to obtain a doped and modified bismuth niobate calcium-based ceramic material.

4. The method for preparing the doped and modified bismuth niobate calcium-based ceramic material according to claim 3, characterized in that, In step S1, the Ca source is CaCO3 powder, the Bi source is Bi2O3 powder, the Nb source is Nb2O5 powder, the M source is M carbonate powder, the Ce source is Ce2O3 powder, the Nd source is Nd2O3 powder, and the W source is WO3 powder.

5. The method for preparing the doped and modified bismuth niobate calcium-based ceramic material according to claim 3, characterized in that, In step S1, the solvent used in the primary wet ball milling is anhydrous ethanol, and the milling medium is zirconia balls; the mass ratio of zirconia balls, raw material and anhydrous ethanol is 5:(1-3):(3-5). And / or, the ball milling time is 12-20 h, and the ball milling speed is 300-350 r / min.

6. The method for preparing the doped and modified bismuth niobate calcium-based ceramic material according to claim 3, characterized in that, In step S2, the pre-sintering atmosphere is air, the temperature is 850 ℃-900 ℃, and the holding time is 2-3 hours. And / or, in step S5, the sintering atmosphere is air, the temperature is 1120 ℃-1200 ℃, and the holding time is 2-3 hours.

7. The method for preparing the doped and modified bismuth niobate calcium-based ceramic material according to claim 3, characterized in that, In step S3, the solvent used in the secondary wet ball milling is anhydrous ethanol, and the milling medium is zirconia balls; the mass ratio of zirconia balls, pre-calcined powder and anhydrous ethanol is 5:(1-3):(3-5). And / or, the ball milling time is 12-20 h, and the ball milling speed is 300-350 r / min.

8. The method for preparing the doped and modified bismuth niobate calcium-based ceramic material according to claim 3, characterized in that, In step S4, the pre-compression molding involves applying a pressure of 0.5-1 MPa to perform preliminary molding; The holding pressure of the cold isostatic pressing is 180-220 MPa, and the holding time is 4-6 min.

9. The method for preparing the doped and modified bismuth niobate calcium-based ceramic material according to claim 3, characterized in that, In step S6, the polarization includes: placing the sintered ceramic sheet coated with the electrode in silicone oil at 130-170 °C, applying a polarization electric field of 15-20 kV / mm, and polarization time of 15-25 min.

10. The application of a doped and modified bismuth calcium niobate-based ceramic material according to claim 1 or 2, or a doped and modified bismuth calcium niobate-based ceramic material obtained by the preparation method according to any one of claims 3-9, characterized in that, The doped and modified bismuth niobate calcium-based ceramic material is used in the field of piezoelectric sensors.

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