A preparation method of a niobium-doped barium titanate ceramic material with improved flexoelectric performance
By using a method for preparing barium titanate ceramic materials doped with niobium, the problem of weak flexural properties in existing ferroelectric materials has been solved, and high flexural coefficient and uniform grains have been achieved, making the materials suitable for practical applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-04
- Publication Date
- 2026-03-24
AI Technical Summary
Existing ferroelectric materials have weak flexural properties, complex manufacturing processes, and low yields, making them difficult to widely use in practical applications.
A method for preparing barium titanate ceramic materials doped with niobium is adopted, including solid-state sintering, pressing of the preform and annealing. The flexural properties are controlled by niobium doping, and semiconductor characteristics are introduced to improve the flexural coefficient of the material.
It significantly improves the flexural conductivity of niobium-doped barium titanate ceramics, reduces grain size and improves uniformity, lowers the Curie temperature of the material, and shortens the preparation cycle, enabling mass production.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of functional materials, and particularly relates to a method for regulating the flexoelectric property of barium titanate (BaTiO3) ceramic material by changing the doping ratio of niobium element. BACKGROUND
[0002] Functional materials are the core of new material development, and force-electric coupling functional materials can realize the conversion between mechanical energy and electrical energy, and are widely applied to filters, sensors, transducers, drivers and energy recovery systems. Force-electric coupling effects mainly include piezoelectric effect, electrostrictive effect and Maxwell effect; and the most widely used force-electric coupling effect is piezoelectric effect. However, piezoelectric materials will lose piezoelectricity above Curie temperature, and the piezoelectricity of lead-free piezoelectric materials is far less than that of lead-containing piezoelectric materials, and lead is an element that can cause damage to the human body and the environment. Therefore, researchers begin to look for other functional materials to replace piezoelectric materials, such as flexoelectric materials. Flexoelectric effect describes the interaction between dielectric polarization and strain gradient.
[0003] Since the strain gradient itself can break the center symmetry structure of the material, flexoelectric effect can exist in all dielectric materials; and the widely studied piezoelectric effect only exists in materials with crystal structure without symmetry center, and therefore, flexoelectric effect is a more widely used force-electric coupling effect than piezoelectric effect. This effect can be used to design some new functional materials and devices. In the research of flexoelectric effect, flexoelectric coefficient μ ijkl is one of the most important parameters used to describe the size of the flexoelectric property of the material, and early theories predict that the flexoelectric coefficient of the material is in the range of 10 -12 ~ 10 -11 C / m, and in recent years, the test results of the flexoelectric coefficient of ferroelectric materials are several orders of magnitude larger than the theoretical prediction, and ferroelectric materials are one of the most promising flexoelectric materials, and have a very wide application prospect in practical applications. However, the flexoelectric effect in current materials is still too weak compared with piezoelectric effect, and it is difficult to produce a relatively large strain gradient in macroscopic solid materials, thus limiting the practical application of flexoelectric effect.
[0004] Studies have shown that materials with high dielectric properties generally have relatively high flexoelectric coefficients. Since ferroelectric oxides have higher dielectric properties than ordinary dielectric materials, the materials with high flexoelectric coefficients obtained at present are basically ferroelectric materials. These materials mainly include BaTiO3-based ferroelectric materials, bismuth-containing ferroelectric materials, lead-containing ferroelectric materials, SrTiO3-based ferroelectric materials, LiNbO3-based ferroelectric materials, (Na, K) NbO3-based ferroelectric materials, and ferroelectric materials with tungsten bronze structure. The flexoelectric coefficient of the current ferroelectric oxide materials is as high as 10 -6 ~ 10-4 C / m, but the currently found materials with high flexoelectric properties (flexoelectric coefficient greater than 10 -4 C / m) have complicated preparation processes, long preparation period and low yield, and affect other properties of the materials. SUMMARY
[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of a niobium-doped barium titanate ceramic material with improved flexoelectric properties. The material preparation method provided by the present application is simple, has a short preparation period, can realize mass production, and does not affect other properties of the material.
[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:
[0007] A preparation method of a niobium-doped barium titanate ceramic material with improved flexoelectric properties, comprising the following steps:
[0008] (1) Preparation of niobium-doped barium titanate powder
[0009] First, dry the BaTiO3 and Nb2O5 powders in an oven, then according to the stoichiometric ratio of the components of the ceramic sample required, calculate the mass of each chemical raw material required for each component, and consider the purity of the chemicals when calculating; then pour the weighed raw materials into a polytetrafluoroethylene ball mill tank containing agate balls, add anhydrous ethanol as the ball milling medium, and perform ball milling on a planetary ball mill; 1-x Nb x O3(0<x<0.05), calculate the mass of each chemical raw material required for each component, and consider the purity of the chemicals when calculating; then pour the weighed raw materials into a polytetrafluoroethylene ball mill tank containing agate balls, add anhydrous ethanol as the ball milling medium, and perform ball milling on a planetary ball mill;
[0010] The well-mixed powders are solid-phase sintered at 1050℃ to 1150℃ for 2h to 3h, which is to make the raw materials chemically react at high temperature to generate the required BaTi 1-x Nb x O3 ceramic crystal phase;
[0011] The sintered powders are further ball-mixed to obtain niobium-doped barium titanate powder;
[0012] (2) Preparation of the to-be-used green body
[0013] Mix and grind the niobium-doped barium titanate powder and the polyvinyl alcohol solution with a mass concentration of 5wt% to 10wt% according to a mass ratio of niobium-doped barium titanate powder to polyvinyl alcohol of 100:1 to 200:1, put the granules into a mold with a diameter of 40mm, and use a hydraulic press to uniaxially press the granules into a green body at a pressure of 200-300MPa; put the green body into a muffle furnace and heat it at 500℃ to 600℃ for 3h to 5h to obtain a to-be-used green body;
[0014] (3) solid phase sintering to prepare the niobium doped barium titanate ceramic
[0015] Put the embryo to be used into a muffle furnace, heat to 1300-1350℃ at a heating rate of 3-5℃ / min, and keep for 3-5h to obtain the niobium doped barium titanate ceramic;
[0016] (4) annealing treatment of the niobium doped barium titanate ceramic
[0017] Put the sintered niobium doped barium titanate ceramic into a muffle furnace, and perform annealing treatment at 800-1000℃ for 6-10h to eliminate the oxygen vacancies caused in the ceramic preparation process.
[0018] The niobium doped barium titanate ceramic material has a niobium doping ratio of 0-5%.
[0019] If the flexoelectric coefficient of the niobium doped barium titanate ceramic material is to be measured, the sintered niobium doped barium titanate ceramic is cut into a cuboid beam structure before the annealing treatment.
[0020] The niobium element doping is a donor doping, which introduces semiconductor characteristics. The niobium element doping can also reduce the Curie temperature of the material and inhibit the growth of ceramic grains, and increase the uniformity of the ceramic grain size. When the niobium doping concentration is 0.2%, the flexoelectric coefficient of the niobium doped barium titanate ceramic ranges from 23 to 380μC / m, and the flexoelectric performance of the optimal component is 20 times higher than that of the pure barium titanate ceramic. The average grain size is reduced from 5.00μm to 1μm, and the ceramic with nanoscale grain size is successfully prepared.
[0021] The beneficial technical effects of the present application are embodied in the following aspects:
[0022] The flexoelectric effect is a force-electric coupling effect induced by strain gradient, which has the characteristics of not being limited by the symmetry of crystal materials and size effect compared with the piezoelectric effect, and has important application potential in micro-nano sensing and driving and energy recovery. However, the flexoelectric performance of ferroelectric materials still cannot replace the piezoelectric effect, so it is necessary to enhance the flexoelectric effect of the material for practical application. Compared with reducing the size of the ceramic to enhance the flexoelectric performance, the method of regulating the flexoelectric performance by niobium element doping is simple to operate, has a wider application range, and is helpful to form fine-grained ceramics with high density. With the doping of niobium element, the grain size of barium titanate ceramic is reduced from 5.00μm to 1μm, and the flexoelectric coefficient is increased from 15.8μC / m to 380.0μC / m. The niobium element doping is a donor doping, which introduces semiconductor characteristics. The niobium element doping can also reduce the Curie temperature of the material and inhibit the growth of ceramic grains, and these factors will have a significant impact on the flexoelectric effect of barium titanate ceramic. Attached Figure Description
[0023] Figures 1(a), 1(b), 1(c), and 1(d) are microstructure diagrams of barium titanate ceramics with different niobium doping ratios prepared in Examples 1, 2, 3, and Comparative Example 1, respectively. Figure 2 The flexural coefficient μ of barium titanate ceramics with different niobium doping ratios at room temperature 12 picture.
[0024] Figure 3 XRD patterns of barium titanate ceramics with different niobium doping ratios. Detailed Implementation
[0025] To further understand the present invention, the preparation method of the niobium-doped barium titanate ceramic material with improved flexural properties provided by the present invention will be described below with reference to embodiments and comparative examples. The scope of protection of the present invention is not limited to the following embodiments.
[0026] The flexural electrical effect was measured as follows: silver paste was applied to the upper and lower surfaces of the sample, with an area A of 15 mm². 2 A silver electrode was used, and copper wires were connected to the electrode with silver paste. The transverse flexural conductivity of the niobium-doped barium titanate ceramic sample was then measured. The transverse flexural conductivity was tested using the three-point bend method. A sinusoidal force with a frequency of 1 Hz was applied to the center of the upper surface of the niobium-doped barium titanate ceramic sample beam. The span of the three-point bend was L = 10 mm. Strain along the length direction and a strain gradient along the thickness direction were observed in the sample. The average strain gradient along the thickness direction was... Where δ is the displacement of the sample center and a is the half-length of the electrode. The polarization charge Q is detected using a charge amplifier and oscilloscope, and the average polarization P can be obtained by P = Q / A. Based on the strain gradient of the sample and the flexural electrical signal measured on the electrode, the transverse flexural electrical coefficient μ is obtained. 12 .
[0027] The materials used in the following examples are described below: BaTiO3 (99.9% pure, Shanghai Wokai Pharmaceutical Co., Ltd.) and Nb2O5 (99.9% pure, Shanghai Maclean Biochemical Technology Co., Ltd.).
[0028] Example 1
[0029] (1) Preparation of niobium-doped barium titanate powder
[0030] BaTiO3(99.9% pure, Shanghai Woke Pharmaceutical Co., Ltd.) and Nb2O5(99.9% pure, Shanghai Maikelin Biochemical Technology Co., Ltd.) powders were dried in an oven, and then BaTiO3 and Nb2O5 powders were weighed according to a molar ratio of 1:0.001. The weighed raw materials were then poured into a polytetrafluoroethylene ball mill tank containing agate balls, and anhydrous ethanol was added as a ball milling medium. After 24 h of planetary ball milling, the mixture was dried and placed in a muffle furnace for solid phase sintering at 1050°C for 2 h. The sintered powder was then ball milled to obtain a niobium-doped barium titanate powder.
[0031] (2) Preparation of a green body
[0032] The niobium-doped barium titanate powder and a polyvinyl alcohol solution with a mass concentration of 5 wt% were mixed and ground in a mortar at a mass ratio of 10:1 to form granules that could pass through a 60-mesh sieve. The granules were placed in a mold with a diameter of 40 mm, and a hydraulic press was used to uniaxially press the granules into a green body at a pressure of 200 MPa. The thickness of the green body was 2 mm. The green body was placed in a muffle furnace and heated at 500°C for 3 h to remove the binder in the green body, thereby obtaining a green body.
[0033] (3) Preparation of a niobium-doped barium titanate ceramic by solid phase sintering
[0034] The green body was placed in a muffle furnace and heated to 1300°C at a heating rate of 3°C / min, and then annealed for 3 h to obtain a niobium-doped barium titanate ceramic. The grain is a small crystal with an irregular shape that makes up a polycrystal. The grain size is an important factor in the microstructure of the ceramic and has a significant impact on the mechanical and electrical properties of the material. In this application, the average grain size of the ceramic was obtained by selecting 400 to 600 grains in the SEM image and measuring their sizes, and then performing Gaussian fitting on the data. According to the SEM image in Figure 1(a), the average grain size of the barium titanate ceramic with a niobium doping ratio of 0.2% was 1.00 μm.
[0035] (4) Cutting of the niobium-doped barium titanate ceramic
[0036] The sintered niobium-doped barium titanate ceramic wafer was cut into a beam with dimensions of 25 mm x 8 mm x 1.5 mm.
[0037] (5) Annealing treatment of the ceramic
[0038] Since the niobium-doped barium titanate ceramic is prone to generate oxygen vacancies at high temperatures, a high concentration of oxygen vacancies can significantly increase the electrical conductivity of the ceramic. In this case, the dielectric and flexoelectric coefficients will be greater than the intrinsic values, so it is necessary to perform annealing treatment on the cut niobium-doped barium titanate ceramic to eliminate the oxygen vacancies caused during the preparation of the ceramic. The cut niobium-doped barium titanate ceramic was placed in a muffle furnace and annealed at 800°C for 6 h.
[0039] (6) Coating electrode
[0040] The surface of the niobium-doped barium titanate ceramic sample was coated with silver paste with an area of 15 mm 2 The copper wire was connected to the electrode with silver paste. The silver paste coated sample was dried at 100°C for 15h, and then was put into a muffle furnace for electrode firing at 550°C for 30min.
[0041] The flexoelectric coefficient was measured by the three-point bending method to be 379.66μC / m.
[0042] Example 2
[0043] (1) Preparation of niobium-doped barium titanate powder
[0044] The BaTiO3(99.9% pure, Shanghai Woke Pharmaceutical Co., Ltd.) and Nb2O5(99.9% pure, Shanghai Maikelin Biochemical Technology Co., Ltd.) powders were dried in an oven, and then BaTiO3and Nb2O5powders were weighed according to a molar ratio of 1:0.002. The weighed raw materials were then poured into a polytetrafluoroethylene ball mill tank containing agate balls, and anhydrous ethanol was added as a ball milling medium. After ball milling in a planetary ball mill for 24h, the mixture was dried and put into a muffle furnace for solid phase sintering at 1100°C for 2.5h. Then the sintered powder was ball milled to obtain the niobium-doped barium titanate powder.
[0045] (2) Preparation of green body
[0046] The niobium-doped barium titanate powder and a polyvinyl alcohol solution with a mass concentration of 8wt% were mixed and ground in a mortar according to a mass ratio of 10:1 to form granules that could pass through a 60 mesh sieve. The granules were placed into a mold with a diameter of 40mm, and a hydraulic press was used to uniaxially press the granules into a green body at a pressure of 250MPa. The thickness of the green body was 2mm. The green body was placed into a muffle furnace and heated at 550°C for 4h to remove the binder, thereby obtaining the green body.
[0047] (3) Solid phase sintering to prepare niobium-doped barium titanate ceramic
[0048] The green body was placed into a muffle furnace and heated to 1325°C at a heating rate of 4°C / min, and then was kept at this temperature for 4h to obtain the niobium-doped barium titanate ceramic. The SEM image of Fig. 1(b) shows that the average grain size of the barium titanate ceramic with a niobium doping ratio of 0.4% was 0.74μm.
[0049] (4) Cutting of niobium-doped barium titanate ceramic
[0050] The sintered niobium-doped barium titanate ceramic wafer was cut into a beam with dimensions of 25mm x 8mm x 1.5mm.
[0051] (5) Annealing treatment of niobium-doped barium titanate ceramics
[0052] The cut niobium-doped barium titanate ceramics were placed in a muffle furnace and annealed at 900℃ for 8 hours to eliminate oxygen vacancies caused during the ceramic preparation process.
[0053] (6) Coated electrodes
[0054] Silver paste was applied to the upper and lower surfaces of the niobium-doped barium titanate ceramic sample, with a total area of 15 mm². 2 A silver electrode was prepared, and a copper wire was connected to the electrode using silver paste. The sample coated with silver paste was dried at 100°C for 15 hours. After drying, it was placed in a muffle furnace and held at 550°C for 30 minutes to prepare the electrode.
[0055] Its flexural conductivity was measured to be 184.78 μC / m using the three-point bending method.
[0056] Example 3
[0057] (1) Preparation of niobium-doped barium titanate powder
[0058] BaTiO3 (99.9% pure, Shanghai Wokai Pharmaceutical Co., Ltd.) and Nb2O5 (99.9% pure, Shanghai Maclean Biochemical Technology Co., Ltd.) powders were dried in an oven. Then, BaTiO3 and Nb2O5 powders were weighed at a molar ratio of 1:0.003. The weighed raw materials were poured into a polytetrafluoroethylene ball mill jar containing agate balls, and anhydrous ethanol was added as the milling medium. After ball milling for 24 hours in a planetary ball mill, the powders were dried and placed in a muffle furnace for solid-state sintering at 1150℃ for 3 hours. The sintered powders were then ball-milled again to obtain niobium-doped barium titanate powder.
[0059] (2) Preparation of embryos for use
[0060] Niobium-doped barium titanate powder and a 10 wt% polyvinyl alcohol solution were mixed and ground in a mortar at a mass ratio of 10:1 to form granules that could pass through a 60-mesh sieve. The granules were then placed in a 40 mm diameter mold and pressed into a preform using a hydraulic press at a pressure of 300 MPa. The preform was 2 mm thick. The preform was then placed in a muffle furnace and held at 600 °C for 5 hours to remove the binder, resulting in the preform ready for use.
[0061] (3) Preparation of niobium-doped barium titanate ceramics by solid-state sintering
[0062] The preform was placed in a muffle furnace and heated to 1350℃ at a heating rate of 5℃ / min, and held at that temperature for 5 hours to obtain niobium-doped barium titanate ceramic. The SEM image in Figure 1(c) shows that the average grain size of the barium titanate ceramic with a niobium doping ratio of 0.6% is 0.73 μm.
[0063] (4) Niobium-doped barium titanate ceramic cutting
[0064] The sintered ceramic discs were cut into beams with dimensions of 25mm × 8mm × 1.5mm.
[0065] (5) Annealing treatment of niobium-doped barium titanate ceramics
[0066] The cut niobium-doped barium titanate ceramics were placed in a muffle furnace and annealed at 1000℃ for 10 hours to eliminate oxygen vacancies caused during the ceramic preparation process.
[0067] (6) Coated electrodes
[0068] Silver paste was applied to the upper and lower surfaces of the niobium-doped barium titanate ceramic sample, with a total area of 15 mm². 2 A silver electrode was prepared, and a copper wire was connected to the electrode using silver paste. The sample coated with silver paste was dried at 100°C for 15 hours. After drying, it was placed in a muffle furnace and held at 550°C for 30 minutes to prepare the electrode.
[0069] Its flexural conductivity was measured to be 22.95 μC / m using the three-point bending method.
[0070] Comparative Example 1
[0071] (1) Preparation of barium titanate preforms
[0072] BaTiO3 (99.9% pure, Shanghai Wokai Pharmaceutical Co., Ltd.) powder was dried in an oven, and then mixed with a 5wt% polyvinyl alcohol solution in a mortar at a mass ratio of 10:1 to granulate, so that the granules could pass through a 60-mesh sieve. The granules were placed in a mold with a diameter of 40 mm and pressed into a preform with a pressure of 200 MPa using a hydraulic press. The preform thickness was 2 mm. The preform was placed in a muffle furnace and kept at 500℃ for 3 hours to remove the binder in the preform, and the preform was ready for use.
[0073] (2) Solid-state sintering for ceramic preparation
[0074] The preforms were placed in a muffle furnace and heated to 1300℃ at a heating rate of 3℃ / min, and held at that temperature for 3 hours to obtain niobium-doped barium titanate ceramics with different proportions. The SEM image in Figure 1(d) showed that the average grain size of the barium titanate ceramics was 5.00 μm.
[0075] (3) Ceramic cutting
[0076] The prepared ceramic discs were cut into beams with dimensions of 25mm × 8mm × 1.5mm.
[0077] (4) Annealing the ceramics
[0078] The fired ceramics are placed in a muffle furnace and annealed at 800℃ for 6 hours to eliminate oxygen vacancies caused during the ceramic preparation process.
[0079] (5) Coating electrodes
[0080] Apply silver paste to the upper and lower surfaces of the sample, covering an area of 15 mm. 2 A silver electrode was prepared, and a copper wire was connected to the electrode using silver paste. The sample coated with silver paste was dried at 100°C for 15 hours. After drying, it was placed in a muffle furnace and held at 550°C for 30 minutes to prepare the electrode.
[0081] Its flexural conductivity was measured to be 15.79 μC / m using the three-point bending method.
[0082] Figures 1(a), 1(b), 1(c), and 1(d) are SEM images of the surface of a 0.2% Nb-doped BaTiO3 ceramic from Example 1, a 0.4% Nb-doped BaTiO3 ceramic from Example 2, a 0.6% Nb-doped BaTiO3 ceramic from Example 3, and a BaTiO3 ceramic from Comparative Example 1, respectively. It can be seen that this invention successfully prepared ceramics with high-density nanoscale grains and uniform grain size distribution. Figure 3 It can be seen that all samples have a tetragonal perovskite structure and no second phase is generated.
[0083] Figure 2 The flexural conductivity of barium titanate ceramics was studied as a function of niobium doping ratio. When the niobium doping concentration was 0.2%, the flexural conductivity reached 380 μC / m, a 20-fold increase compared to pure barium titanate ceramics. Furthermore, the average grain size decreased from 5.00 μm to 1 μm, successfully fabricating ceramics with nanoscale grains. The use of niobium as a donor doping element introduces semiconductor properties. Niobium doping also lowers the Curie temperature, inhibits grain growth, and increases grain size uniformity, all of which significantly influence the flexural conductivity of barium titanate ceramics.
[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing niobium-doped barium titanate ceramic materials with improved flexural electrical properties, characterized in that, The specific steps are as follows: (1) Preparation of niobium-doped barium titanate powder First, dry the BaTiO3 and Nb2O5 powders in an oven, then adjust the BaTiO3 powder according to the required stoichiometric ratio of the ceramic sample components. 1-x Nb x O3, where 0 < x < 0.004, calculate the mass of each chemical raw material required for each component, taking into account the purity of the chemical raw materials during the calculation; then pour the weighed raw materials into a ball mill jar, add anhydrous ethanol as the ball milling medium, and ball mill on a ball mill. The thoroughly mixed powder is then subjected to solid-state sintering at 1050℃ to 1150℃ for 2 to 3 hours, allowing the raw materials to undergo a chemical reaction at high temperature to generate the desired BaTi. 1-x Nb x O3 ceramic crystal phase; The sintered powder is then ball-milled and mixed to obtain niobium-doped barium titanate powder. (2) Preparation of embryos for use Niobium-doped barium titanate powder and a polyvinyl alcohol solution with a mass concentration of 5 wt% to 10 wt% are mixed, ground, and granulated at a mass ratio of 100:1 to 200:
1. The granules are then uniaxially pressed into preforms in a mold. The preforms are placed in a muffle furnace and held at 500°C to 600°C for 3 to 5 hours to obtain the preforms ready for use. (3) Preparation of niobium-doped barium titanate ceramics by solid-state sintering The blank to be used is placed in a muffle furnace and heated to 1300℃ to 1350℃ at a heating rate of 3℃ / min to 5℃ / min, and held for 3h to 5h to obtain niobium-doped barium titanate ceramic. (4) Annealing treatment of niobium-doped barium titanate ceramics The sintered niobium-doped barium titanate ceramics are placed in a muffle furnace and annealed at 800℃ to 1000℃ for 6 to 10 hours to eliminate oxygen vacancies caused during the preparation of niobium-doped barium titanate ceramics. The flexural conductivity of niobium-doped barium titanate ceramics ranges from 23 μC / m to 380 μC / m.
2. The method for preparing niobium-doped barium titanate ceramic material with improved flexural electrical properties according to claim 1, characterized in that: First, the sintered niobium-doped barium titanate ceramic is cut into a cuboid beam structure, the flexural conductivity of the niobium-doped barium titanate ceramic material is measured, and then it is annealed.
3. The method for preparing niobium-doped barium titanate ceramic material with improved flexural electrical properties according to claim 1, characterized in that: In step (1), the purity of barium titanate and niobium oxide powder is ≥99.9% and the particle size is 100nm.