Sodium bismuth titanate ceramic capacitor dielectric material and preparation method thereof

Abstract

The invention provides a sodium bismuth titanate ceramic capacitor dielectric material and a preparation method thereof, the chemical general formula of the sodium bismuth titanate ceramic capacitor dielectric material is (1-x) (0.7 Bi < 0.5 > Na < 0.5 > TiO < 3 >-0.3 K < 0.5 > Na < 0.5 > NbO < 3 >)-xSr < 0.7 > Bi < 0.2 > Ca < 0.1 > TiO < 3 >, x is a molar coefficient, and x is more than or equal to 0.1 and less than or equal to 0.18. According to the sodium bismuth titanate ceramic capacitor dielectric material, the high-polarization and high-energy-storage-density sodium bismuth titanate ceramic capacitor dielectric material is obtained through relaxation design and reduction of oxygen vacancy concentration.

Description

Technical Field

[0001] This invention belongs to the technical field of dielectric energy storage ceramic materials, specifically relating to a sodium bismuth titanate ceramic capacitor dielectric material and its preparation method. Background Technology

[0002] Ceramic capacitors are key energy storage components with wide applications in various fields such as electronics, power, defense, transportation, and new energy, playing a particularly important role in high-power pulse power supplies, energy storage devices, and frequency filters. These capacitors are typically composed of ceramic-based dielectric materials and electrode materials, with the performance of the dielectric material directly determining the capacitor's energy density, breakdown field strength, and operating efficiency.

[0003] Currently, ceramic-based dielectric materials are attracting increasing attention due to their excellent mechanical strength and thermal stability. Based on different dielectric polarization behaviors, ceramics can be classified into four types: linear dielectrics, ferroelectrics, relaxor ferroelectrics, and antiferroelectrics. Taking relaxor ferroelectrics as an example, due to the presence of highly dynamic polar nanoregions (PNRs) within them, they can rapidly respond to and align along the direction of an applied electric field, generating extremely high polarization intensity. However, after the electric field is removed, they can return to their initial state, exhibiting low remanent polarization intensity. This results in relaxor ferroelectrics possessing high effective energy storage density and excellent energy storage efficiency. Therefore, inducing relaxation behavior is a common method to improve the energy storage performance of ceramics.

[0004] Depending on the type of material, ceramic-based dielectrics include bismuth ferrite (BiFeO3, abbreviated as BF), barium titanate (BaTiO3, abbreviated as BT), and sodium bismuth titanate (Bi). 0.5 Na 0.5 TiO3 (BNT) and potassium sodium niobate (K 0.5 Na 0.5 TiO3 (KNN) and other materials possess high dielectric constants, strong polarization characteristics, and low dielectric losses. Among them, lead-free ceramic materials (BNTs), with their high saturation polarization and high Curie temperature, are gradually becoming an important direction in energy storage material research, especially showing superior application potential in harsh environments such as high temperature and high frequency. However, their large coercive electric field and low breakdown strength are the main bottlenecks limiting their energy storage performance. To address this, KNN, which can enhance ionic polarization and refine grain size, is introduced into BNTs to induce the transformation of BNTs from ferroelectric to relaxor, constructing BNT-KNN-based ceramics, which improves the breakdown field strength to some extent.

[0005] Although the introduction of KNN improves the performance of pure BNT matrix, low energy storage efficiency and poor stability remain significant limitations of BNT-KNN based ceramics. Therefore, improving energy storage density and optimizing dielectric properties and breakdown strength have become the core objectives of research on sodium bismuth titanate ceramic capacitors. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a sodium bismuth titanate ceramic capacitor dielectric material. By relaxation design and reducing the oxygen vacancy concentration, a sodium bismuth titanate ceramic capacitor dielectric material with high polarization and high energy storage density can be obtained.

[0007] This invention provides a bismuth sodium titanate ceramic capacitor dielectric material with the general chemical formula (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3, in which x The molar coefficient, x The value range is 0.1≤ x ≤0.18.

[0008] In the bismuth sodium titanate ceramic capacitor dielectric material provided by this invention, 0.7Bi is selected. 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 Using NbO3 (BNT-KNN) as the first matrix, relaxor units Sr are introduced into sodium titanate. 0.7 Bi 0.2 Ca 0.1 TiO3 (abbreviated as SBCT), in which Sr 3+ It can effectively suppress grain growth and induce strong relaxation behavior on the BNT-KNN matrix, thus exhibiting a fine hysteresis loop and improving energy storage performance; Bi 3+ It can replenish the Bi element that volatilizes in sodium bismuth titanate due to high-temperature sintering, preventing chemical composition shifts and the formation of a second phase; Ca 2+ This invention effectively reduces oxygen vacancy concentration, preventing the formation of conductive pathways within the structure due to increased oxygen vacancy concentration, which would lead to increased leakage current and decreased breakdown field strength. The invention provides a ceramic capacitor dielectric material that, through relaxation design and reduction of oxygen vacancy concentration, achieves a sodium bismuth titanate ceramic capacitor dielectric material with high polarization and high energy density.

[0009] This invention also provides a method for preparing the above-mentioned sodium bismuth titanate ceramic capacitor dielectric material, comprising the following steps: weighing Bi2O3, TiO2, Nb2O5, Na2CO3, K2CO3, SrCO3, and CaCO3 as raw materials according to the stoichiometric ratio of the general chemical formula and mixing them evenly; ball milling the raw materials once and pre-firing them at high temperature, then ball milling them a second time; granulating the pre-firing powder after the second ball milling to obtain granulated powder; dry pressing the granulated powder to obtain an initial green body; removing the binder from the initial green body to obtain a ceramic green body; sintering the ceramic green body after removing the binder to obtain the sodium bismuth titanate ceramic capacitor dielectric material.

[0010] In the preparation method of the bismuth sodium titanate ceramic capacitor dielectric material provided by this invention, BNT-KNN is selected as the first matrix, and oxides Bi2O3 and TiO2, as well as carbonates Na2CO3 and CaCO3, are added according to a predetermined chemical ratio. Sr is then deposited at a high temperature at the microscopic level. 3+ Bi 3+ Ca 2+ By integrating sodium bismuth titanate ceramic capacitor dielectric material into the main lattice of the matrix crystal and through relaxation design and reduction of oxygen vacancy concentration, high polarization and high energy storage density can be obtained.

[0011] Furthermore, in the step of weighing and uniformly mixing Bi₂O₃, TiO₂, Nb₂O₅, Na₂CO₃, K₂CO₃, SrCO₃, and CaCO₃ as raw materials according to the stoichiometric ratio of the general chemical formula, an excess molar fraction of Bi₂O₃ is added during weighing. Since a high-temperature sintering process is required, bismuth is easily volatilized at high temperatures; therefore, an excess of Bi₂O₃ is added during weighing to compensate for the volatilized Bi element.

[0012] Furthermore, the raw materials are ball-milled once, and the raw materials from the first ball milling are pre-fired at high temperature to obtain pre-fired powder. The pre-fired powder is then ball-milled a second time, and the pre-fired powder after the second ball milling is granulated to obtain granulated powder. In the first ball milling of the raw materials, the weighed raw materials are placed in a nylon ball mill jar, and an appropriate amount of anhydrous ethanol and zirconium oxide beads of different particle sizes are added as grinding media. In the second ball milling of the pre-fired powder, the pre-fired powder is placed in a nylon ball mill jar, and an appropriate amount of anhydrous ethanol and zirconium oxide beads of different particle sizes are added as grinding media. Performing the first and second ball milling breaks up agglomerates, obtaining finer particles and more uniformly mixed powder, which is beneficial for improving reactivity and the densification of the ceramic.

[0013] Furthermore, the raw materials are ball-milled once, and the ball-milled raw materials are pre-fired at high temperature to obtain pre-fired powder. The pre-fired powder is then ball-milled a second time, and the pre-fired powder after the second ball milling is granulated to obtain granulated powder. During the high-temperature pre-fired process, the ball-milled raw materials are held at 800-900℃ for 3 hours. After pre-fired, they are cooled to room temperature to obtain pre-fired powder. This process allows for a solid-state reaction between carbonates and oxides, pre-sintering to form the precursor of the target phase and decomposing volatile impurities, thereby improving powder purity and reactivity, and enhancing ceramic density.

[0014] Furthermore, the raw materials are ball-milled once, and the ball-milled raw materials are pre-fired at high temperature to obtain pre-fired powder. The pre-fired powder is then ball-milled a second time, and the pre-fired powder after the second ball milling is granulated to obtain granulated powder. In this step, an appropriate amount of binder is added to the pre-fired powder after the second ball milling, and the mixture is ground and then screened through a sieve to obtain granulated powder. Adding binder and screening through a sieve results in grains with uniform particle size, forming granulated powder with good flowability and uniform particle size, which facilitates subsequent tableting and effectively avoids cracking and delamination in ceramics.

[0015] Furthermore, in the step of dry pressing the granulated powder to obtain the initial green body, the granulated powder is weighed and placed in a mold, and pressure is applied in one direction to obtain the initial green body. Dry pressing the granulated powder causes the granulated powder to be tightly arranged under the action of external force, which improves the initial density of the green body and provides a stable structural basis for subsequent high-temperature sintering.

[0016] Furthermore, in the step of removing the binder from the initial green body to obtain the ceramic green body, the initial green body is heated to 300℃ and held at that temperature; then the temperature is raised from 300℃ to 55℃ and held at that temperature to obtain the ceramic green body. Thoroughly removing the binder from the initial green body prevents residual organic matter from deteriorating the final performance of the ceramic.

[0017] Further, in the step of sintering the debinded ceramic preform to obtain the sodium bismuth titanate ceramic capacitor dielectric material, the debinded ceramic preform is held at 1100-1180℃ with a heating rate controlled at 5-8℃ / min to obtain the sodium bismuth titanate ceramic capacitor dielectric material. Controlling the sintering temperature promotes sufficient grain growth and complete reaction of the raw materials, resulting in a dense perovskite structure within the ceramic.

[0018] The present invention also provides a ceramic capacitor comprising the above-mentioned sodium bismuth titanate ceramic capacitor dielectric material. The ceramic capacitor provided by the present invention exhibits high polarization and high energy storage density.

[0019] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0020] Figure 1This is a flowchart of the preparation method of the sodium bismuth titanate ceramic capacitor dielectric material in Example 2.

[0021] Figure 2 This is a flowchart of the capacitor preparation method using sodium bismuth titanate ceramic capacitor dielectric material in Example 3.

[0022] Figure 3 This is a comparison of XRD diffraction patterns of BNT-KNN-xSBCT ceramic and BNT-KNN matrix.

[0023] Figure 4 This is a SEM characterization image of the BNT-KNN-xSBCT (x = 0.16) ceramic from Example 3.

[0024] Figure 5 This is a graph showing the energy storage performance analysis of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3.

[0025] Figure 6 This is a fatigue stability analysis test diagram of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3.

[0026] Figure 7 This is a frequency stability analysis test diagram of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3.

[0027] Figure 8 This is a temperature stability analysis test chart of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3.

[0028] Figure 9 The following are the underdamped response curves, current density (CD), and power density (PD) analysis test graphs of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3.

[0029] Figure 10 The overdamping and discharge energy density (W) of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3 are discussed. dis )Analyze the test chart. Detailed Implementation

[0030] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and not intended to limit the scope of the invention. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the embodiments of the present invention, and not all structures.

[0031] Example 1 This embodiment provides a sodium bismuth titanate ceramic capacitor dielectric material, with the general chemical formula (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3, in which x The molar coefficient, x The value range is 0.1≤ x ≤0.18.

[0032] The sodium bismuth titanate ceramic capacitor dielectric material provided in this embodiment (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 In TiO3 (abbreviated as BNT-KNN-xSBCT), 0.7Bi is selected. 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 Using NbO3 (BNT-KNN) as the first matrix, relaxor units Sr are introduced into sodium titanate. 0.7 Bi 0.2 Ca 0.1 TiO3 (abbreviated as SBCT), in which Sr 3+ It can effectively suppress grain growth and induce strong relaxation behavior on the BNT-KNN matrix, thus exhibiting a fine hysteresis loop and improving energy storage performance; Bi 3+ It can replenish the Bi element that volatilizes in sodium bismuth titanate due to high-temperature sintering, preventing chemical composition shifts and the formation of a second phase; Ca 2+ This invention effectively reduces oxygen vacancy concentration, preventing the formation of conductive pathways within the structure due to increased oxygen vacancy concentration, which would lead to increased leakage current and decreased breakdown field strength. The invention provides a ceramic capacitor dielectric material that, through relaxation design and reduction of oxygen vacancy concentration, achieves a sodium bismuth titanate ceramic capacitor dielectric material with high polarization and high energy density.

[0033] In one embodiment, (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3 x The value is 0.1.

[0034] In one embodiment, (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3 x The value is 0.12.

[0035] In one implementation, (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3 x The value is 0.14.

[0036] In one implementation, (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3 x The value is 0.16.

[0037] In one implementation, (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3 x The value is 0.18.

[0038] Example 2 This embodiment provides a method for preparing the sodium bismuth titanate ceramic capacitor dielectric material of Example 1. Figure 1 This is a flowchart illustrating the preparation method of sodium bismuth titanate ceramic capacitor dielectric material. Please refer to it. Figure 1 The preparation method of sodium bismuth titanate ceramic capacitor dielectric material includes the following steps: Step S1: Weigh out Bi2O3, TiO2, Nb2O5, Na2CO3, K2CO3, SrCO3, and CaCO3 as raw materials according to the stoichiometric ratio of the general chemical formula and mix them evenly; Step S2: After ball milling the raw material once, it is pre-calcined at high temperature to obtain pre-calcined powder, and then ball milled a second time. The pre-calcined powder after the second ball milling is granulated to obtain granulated powder. Step S3: Dry press the granulated powder into an initial preform; Step S4: Remove the binder from the initial green body to obtain a ceramic green body; Step S5: Sinter the ceramic preform after glue removal to obtain sodium bismuth titanate ceramic capacitor dielectric material.

[0039] In the preparation method of the bismuth sodium titanate ceramic capacitor dielectric material provided by this invention, BNT-KNN is selected as the first matrix, and oxides Bi2O3 and TiO2, as well as carbonates Na2CO3 and CaCO3, are added according to a predetermined chemical ratio. Sr is then deposited at a high temperature at the microscopic level. 3+ Bi 3+ Ca 2+ By integrating sodium bismuth titanate ceramic capacitor dielectric material into the main lattice of the matrix crystal and through relaxation design and reduction of oxygen vacancy concentration, high polarization and high energy storage density can be obtained.

[0040] In step S1, according to the stoichiometric ratio of the general chemical formula, Bi₂O₃, TiO₂, Nb₂O₅, Na₂CO₃, K₂CO₃, SrCO₃, and CaCO₃ are weighed and mixed evenly. An excess of 5% molar fraction of Bi₂O₃ is added during weighing. Since a high-temperature sintering process is required, bismuth is easily volatilized at high temperatures; therefore, an excess of Bi₂O₃ is added during weighing to compensate for the volatilized Bi element.

[0041] In step S2, during the first ball milling of the raw materials, the weighed raw materials are placed into a nylon ball mill jar, and an appropriate amount of anhydrous ethanol and zirconia beads of different particle sizes are added as grinding media. The mixture is then ball milled for 20-24 hours. During the second ball milling of the pre-fired powder, the pre-fired powder is placed into a nylon ball mill jar, and an appropriate amount of anhydrous ethanol and zirconia beads of different particle sizes are added as grinding media. The mixture is then ball milled for 20-24 hours. Performing both the first and second ball milling processes breaks up agglomerates, resulting in finer, more uniformly mixed powders, which is beneficial for improving reactivity and the densification of the ceramic.

[0042] In step S2, the raw material from the first ball mill is pre-fired at a high temperature. The raw material is held at 800-900℃ for 3 hours for pre-firing, and then cooled to room temperature to obtain pre-fired powder. This process allows carbonates and oxides to undergo a solid-state reaction, pre-sintering to form a precursor of the target phase and decomposing volatile impurities, thereby improving powder purity and reactivity, and improving ceramic density.

[0043] In step S2, a suitable amount of polyvinyl alcohol solution as a binder, with a concentration of 5%, is added to the pre-fired powder that has undergone secondary ball milling. The powder is then ground using an agate mortar and sieved through a screen to obtain granulated powder. Adding the polyvinyl alcohol binder solution and sieving through a screen results in uniformly sized grains, forming granulated powder with good flowability and uniform particle size. This facilitates subsequent tableting and effectively prevents cracking and delamination in the ceramic.

[0044] In step S3, the granulated powder is weighed and placed in a mold, and pressure is applied in one direction to obtain an initial green body. The granulated powder is then dry-pressed to make the granulated powder tightly packed under the action of external force, thereby increasing the initial density of the green body and providing a stable structural basis for subsequent high-temperature sintering.

[0045] In step S4, the initial green body is heated to 300℃ and held at that temperature; then the temperature is increased from 300℃ to 550℃ and held at that temperature to obtain the ceramic green body. The initial green body is thoroughly debonded to prevent residual organic matter from deteriorating the final performance of the ceramic.

[0046] In step S5, the debinding ceramic preform is held at 1100-1180℃ with a heating rate controlled at 5-8℃ / min to obtain the sodium bismuth titanate ceramic capacitor dielectric material. Controlling the sintering temperature promotes full grain growth and complete reaction of the raw materials, resulting in a dense perovskite structure within the ceramic.

[0047] Example 3 This embodiment provides a method for preparing a dielectric material for a sodium bismuth titanate ceramic capacitor, including the following steps: Step S1: According to 0.84 (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)-0.16Sr 0.7 Bi 0.2 Ca 0.1Based on the stoichiometric ratio of the general chemical formula for TiO3, Bi2O3, TiO2, Nb2O5, Na2CO3, K2CO3, SrCO3, and CaCO3 were weighed and mixed evenly. The total mass of the raw materials was 10g, and an electronic balance with a weighing accuracy of 0.0001 was used. Since subsequent steps require a high-temperature sintering process, and bismuth is easily volatilized at high temperatures, an excess of 5% Bi2O3 was added during weighing.

[0048]

[0049] Step S2: After ball milling the raw material once, pre-calcining it at high temperature, and then ball milling it a second time, granulating the pre-calcined powder after the second ball milling to obtain granulated powder: S201: Ball mill the raw materials in one step. Weigh the raw materials (Bi2O3, TiO2, Nb2O5, Na2CO3, K2CO3, SrCO3, CaCO3) and place them in a nylon ball mill jar. Add an appropriate amount of anhydrous ethanol and zirconia beads of different particle sizes as grinding media. Ball mill at 400 r / min for 20-24 hours. After ball milling, dry in an 80℃ oven for 6 hours to obtain the pre-milled powder. The anhydrous ethanol level must ensure complete immersion of the raw material layer. The total mass ratio of raw materials to total zirconia beads is 1:3. The zirconia beads used are of three diameters: large (8-9 mm), medium (5-6 mm), and small (2-3 mm), with a quantity ratio of 1:2:3. This step significantly improves the fineness and component uniformity of the powder, avoids component segregation, and facilitates the full progress of subsequent reactions.

[0050] S202: High-temperature pre-sintering. After drying the pre-milled powder, it is gently ground in an agate mortar and pestle and placed in a semi-sealed alumina crucible. The crucible is heated to 800℃ in an air atmosphere in a muffle furnace and held for 3 hours at a rate of 5℃ / min. After completion, it is cooled to room temperature to obtain pre-sintered powder. This process allows for solid-state reactions between carbonates and oxides, pre-sintering to form precursors of the target phase and decomposing volatile impurities, thereby improving powder purity and reactivity, and enhancing ceramic density.

[0051] S203: Granulation Treatment. A suitable amount of 5% polyvinyl alcohol solution is added to the pre-fired powder that has undergone secondary ball milling. The powder is then ground in an agate mortar for 30 minutes and sieved through a 120-mesh screen to obtain granulated powder with good flowability and uniform particle size. A binder polyvinyl alcohol solution is added and sieved again to obtain crystals with uniform particle size, forming granulated powder with good flowability and uniform particle size. This facilitates subsequent tableting and effectively prevents cracking and delamination in the ceramic.

[0052] Step S3: Dry-press the granulated powder to obtain the initial preform. 0.5g of granulated powder was weighed using an electronic balance and placed in a mold. A unidirectional pressure of 10MPa was applied for 1 minute to obtain a ceramic green body with a diameter of approximately 11mm and a thickness of approximately 1mm, ensuring that its morphology was regular and its density was uniform. Dry pressing of the granulated powder allowed the granules to be tightly packed under external force, increasing the initial density of the green body and providing a stable structural foundation for subsequent high-temperature sintering. Furthermore, granulation molding is a simple and low-cost operation, suitable for green bodies with simple shapes and small dimensions.

[0053] Step S4: Remove the glue from the initial body to obtain a ceramic body.

[0054] The dry-pressed ceramic blank is placed in a muffle furnace and the program is set as follows: the heating rate is controlled at 5℃ / min throughout the process, first heating from room temperature to 300℃ and holding for 60min; then heating from 300℃ to 550℃ and holding for 180min to ensure sufficient removal of binder and avoid organic residues that could lead to a deterioration in the final performance of the ceramic.

[0055] Step S5: Sinter the debinding ceramic preform to obtain the dielectric material of sodium bismuth titanate ceramic capacitor. Place the debinding ceramic preform in a muffle furnace and hold at 1100-1180℃ for 120 min, with a heating rate controlled at 5-8℃ / min, to obtain 0.84(0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)-0.16Sr 0.7 Bi 0.2 Ca 0.1 TiO3. The purpose of this step is to promote sufficient grain growth and complete reaction of the raw materials, resulting in a dense perovskite structure within the ceramic. To reduce bismuth volatilization at high temperatures, a buried sintering method is used. This involves laying a layer of BNT-KNN-xSBCT powder of the same composition on both the top and bottom of the ceramic body, calcining it at a constant temperature in air, and then naturally cooling it to room temperature. The sintering process promotes grain growth and complete phase structure formation, effectively reducing porosity and improving the mechanical strength and electrical properties of the ceramic.

[0056] To facilitate performance testing of the BNT-KNN-xSBCT ceramic prepared by the above method, the ceramic needs to be polished and the bottom and top electrodes electroplated to form a simple ceramic capacitor. Figure 2 This is a flowchart illustrating the capacitor fabrication process using sodium bismuth titanate ceramic capacitor dielectric material. Please refer to [link / reference]. Figure 2 The following steps are added after the preparation process of BNT-KNN-xSBCT ceramics: Step S6: Polish the dielectric material of the sodium bismuth titanate ceramic capacitor. The sintered 0.84 (0.7Bi)0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)-0.16Sr 0.7 Bi 0.2 Ca 0.1 The TiO3 ceramic sample was polished to a thickness of 0.2 mm using 1000-mesh green silicon carbide abrasive. To prevent the ceramic sheet from cracking due to excessive thinness, the abrasive was then replaced with 3000-mesh abrasive and polishing continued to approximately 0.1 mm thick, with alcohol sprayed onto the abrasive to maintain moisture during the process. Finally, a smooth, uniformly thick ceramic sheet was obtained. This step removes surface defects, ensuring the reliability and repeatability of the sample in performance testing.

[0057] Step S7: Prepare bottom and top electrodes on both sides of the dielectric material of the sodium bismuth titanate ceramic capacitor. Electrode preparation aims to impart good conductivity to the ceramic sample, typically by uniformly depositing a thin metal film on both sides of the ceramic sheet. Common electrode materials include gold (Au), silver (Ag), copper (Cu), and nickel (Ni). In this embodiment, Au is used as the electrode. There are various methods for depositing metal films, such as ion sputtering, magnetron sputtering, electron beam evaporation, pulsed laser deposition, ion beam deposition, and chemical vapor deposition. This embodiment uses ion sputtering, applying a high voltage of approximately 1500V in a vacuum environment to ionize the residual gas and form plasma. Ions in the plasma bombard the metal target under the influence of the electric field, causing target atoms to sputter and deposit onto the ceramic surface, forming a dense conductive film. The advantages of this method are strong adhesion between the film and the substrate, high deposition efficiency, and a uniform and dense film, ensuring the stability and reliability of the electrode.

[0058] The process of depositing the bottom electrode and the top electrode is as follows: First, the ceramic sheet obtained in step S6 is placed in a small ion sputtering instrument, and a vacuum is drawn to a vacuum degree of 2×10⁻⁶. -3 Pa, then introduce an appropriate amount of argon gas, at which point the vacuum level rises back to 2 × 10⁻⁶. - 1 Pa; Using Au as the target material, sputtering is performed on the target material with a sputtering current of 8 mA and a sputtering time of 50 seconds. The above sputtering operation is repeated 4 times to obtain the bottom electrode; then, a perforated mask is placed on the ceramic side without electrode plating, with a hole diameter of 1.5 mm. The above operation steps are repeated to obtain the top electrode.

[0059] The following are the relevant performance tests performed on the dielectric material of the sodium bismuth titanate ceramic capacitor in Example 3: Figure 3This is a comparison of XRD diffraction patterns between BNT-KNN-xSBCT ceramics and the BNT-KNN matrix, where x ranges from 0.1 to 0.18. The test results were obtained using a X-ray diffractometer (model X'Pert PRO, PANalytical X). All samples exhibited a typical perovskite phase structure, with no obvious impurity peaks observed; only slight variations in peak shape were observed, indicating that within the doping range, Sr... 2+ Bi 3+ Ca 2+ The doped sample integrates well into the main lattice of BNT-KNN without disrupting the overall phase structure. Furthermore, compared to pure BNT-KNN, the doped sample exhibits enhanced diffraction peak intensity and a slightly reduced full width at half maximum (FWHM), indicating improved crystallinity and a more complete crystal structure. These results demonstrate that introducing SBCT can yield perovskite ceramics with uniform composition and stable structure, laying the foundation for further improvements in their electrical properties and energy storage characteristics.

[0060] Figure 4 This is a SEM image of the BNT-KNN-xSBCT (x = 0.16) ceramic from Example 3, obtained using a scanning electron microscope (ZEISS Gemini500). All samples were pore-free, exhibiting clear grain boundaries and a dense microstructure. Analysis using Nano Measurer software yielded an average particle size of 0.23 μm, attributed to the larger Sr ionic radius. 2+ (r = 1.44 Å) replaced Na with a smaller ionic radius. + (r = 1.39 Å) and Bi 3+ (r = 1.38 Å), which leads to a decrease in ion mobility, inhibits grain growth, and thus forms small-sized grains. Grain refinement can enrich grain boundaries, lengthen the breakdown path, and help improve the breakdown field strength and energy storage performance.

[0061] Figure 5 This is a graph showing the energy storage performance analysis of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3. The test results were obtained using a ferroelectric tester (Radiant Technology Ferroelectric Tester). Figure 5 (a) is a graph showing the variation of the unipolar PE loop of the BNT-KNN-xSBCT (x = 0.16) ceramic with the electric field. Figure 5 (b) shows the trends of energy storage density Wrec and efficiency η for the BNT-KNN-xSBCT (x = 0.16) ceramic. Please refer to [link / reference]. Figure 5 (a) and Figure 5(b) The dielectric material BNT-KNN-xSBCT (x = 0.16) of the sodium bismuth titanate ceramic capacitor achieved a capacitance of 6.7 J / cm at an electric field strength of 343 kV / cm. 3 The recyclable energy storage density and energy storage efficiency of 84.6% are superior to most BNT-based ceramics. Meanwhile, the polarization difference of the dielectric material BNT-KNN-xSBCT (x = 0.16) for this bismuth sodium titanate ceramic capacitor is 48.2 μC / cm. 2 This is a key factor in achieving high energy storage.

[0062] Continue using the ferroelectric apparatus for 0.84 (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)-0.16Sr 0.7 Bi 0.2 Ca 0.1 Stability tests were conducted on TiO3 ceramics.

[0063] Figure 6 This is a fatigue stability analysis test chart of the BNT-KNN-xSBCT (x = 0.16) ceramic from Example 3, in which... Figure 6 (a) is the PE hysteresis plot of BNT-KNN-xSBCT (x = 0.16) ceramic. Figure 6 (b) is a graph showing the trend of cycle number and efficiency for the BNT-KNN-xSBCT (x= 0.16) ceramic. Please refer to [link / reference]. Figure 6 The sample was subjected to long-cycle electrical fatigue testing at 25℃, 100Hz, and an electric field of 180kV / cm, with the number of cycles reaching 1×10⁻⁶. 6 The PE hysteresis loop of the sample remained stable under different cycle counts, and the polarization intensity did not show significant attenuation. Further calculations showed that the energy storage density of the ceramic changed by less than 1.9% and the energy storage efficiency fluctuated by less than 2.1% throughout the entire cycle. These results indicate that the sodium bismuth titanate ceramic capacitor dielectric material of this embodiment maintains excellent electrical stability under long-term cycling, exhibiting good fatigue resistance and reliability, and is suitable for long-term application in high-frequency, high-power capacitors.

[0064] Figure 7 This is a frequency stability analysis test chart of the BNT-KNN-xSBCT (x = 0.16) ceramic from Example 3, in which... Figure 7 (a) is a graph showing the variation of energy storage performance of BNT-KNN-xSBCT (x = 0.16) ceramic at different frequencies. Figure 7(b) is a graph showing the efficiency variation trend of the BNT-KNN-xSBCT (x = 0.16) ceramic at different frequencies. Please refer to [link / reference]. Figure 7 The energy storage performance of the sample was evaluated at different frequencies (10 Hz, 50 Hz, 100 Hz, 200 Hz, 500 Hz, and 1000 Hz) under conditions of 25 ℃ and 180 kV / cm. The test results showed that the P-E loop morphology of the sample remained intact as the frequency of the applied electric field increased, with only slight changes in polarization intensity and loop area. Quantitative analysis indicated that the energy storage density fluctuated by less than 2.6% at each frequency, and the maximum variation in energy efficiency did not exceed 5.1%. These results demonstrate that the material has strong adaptability to frequency perturbations and can maintain stable energy storage output and conversion efficiency in the low-frequency to kilohertz range, making it suitable for wideband applications.

[0065] Figure 8 This is a temperature stability analysis test chart of the BNT-KNN-xSBCT (x = 0.16) ceramic from Example 3. Figure 8 This is a graph showing the energy storage performance of BNT-KNN-xSBCT (x = 0.16) ceramic at different temperatures. Figure 8 (b) shows the efficiency trend of BNT-KNN-xSBCT (x = 0.16) ceramic at different temperatures. The energy storage performance of the sample was tested in the range of 25℃ to 130℃ at 100 Hz and 180 kV / cm, specifically at 25℃, 50℃, 75℃, 100℃, 110℃, 120℃, and 130℃. Experimental results show that the overall morphology of the P-E loop remains stable with increasing temperature, without significant distortion or polarization attenuation. Calculation results show that the fluctuation range of energy storage density is less than 2.8%, and the change in energy efficiency is less than 4.4%. Therefore, the ceramic dielectric material of this embodiment can maintain excellent electrical properties over a wide temperature range, exhibiting outstanding thermal stability and environmental adaptability, providing a guarantee for its long-term application under complex working conditions.

[0066] Figure 9 The figures show the underdamped response curve, current density (CD), and power density (PD) analysis test results of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3. Figure 9 (a) is the underdamped response curve of the BNT-KNN-xSBCT (x = 0.16) ceramic. Figure 9 (b) shows the current density (CD) and power density (PD) analysis results for the BNT-KNN-xSBCT (x = 0.16) ceramic. Please refer to [link / reference]. Figure 9As the applied electric field gradually increased from 10 kV / cm to 110 kV / cm, the maximum amplified current of the sample increased from 1.1 A to 20.3 A, exhibiting typical field dependence. Further, according to the formula:

[0067]

[0068] Where S is the effective electrode area, the calculation results show that the peak current density of the sample reaches 2583 A / cm at 110 kV / cm. 2 The corresponding power density is as high as 142MW / cm². 3 This indicates that ceramics can achieve a fast and strong discharge effect, and have both high current output capability and power density, showing their application potential in high-power pulse energy storage devices.

[0069] Figure 10 The overdamping and discharge energy density (W) of the BNT-KNN-xSBCT (x = 0.16) ceramic in Example 3 are discussed. dis )Analyze the test chart, among which, Figure 10 (a) is the overdamping curve of the BNT-KNN-xSBCT (x = 0.16) ceramic. Figure 10 (b) is the discharge energy density (W) dis Analyze the test chart. Please refer to [link / reference]. Figure 10 As the applied electric field strength gradually increases, the discharge current curve exhibits a typical single-peak characteristic, with the peak value increasing with the increase of the electric field. No obvious oscillation signal appears, indicating that the system is in an overdamped state. Calculations are based on the formula:

[0070] Where R (218Ω) and V represent the load and ceramic volume, respectively, the results show that Wdis reaches 13.4 J / cm at 130 kV / cm. 3 Simultaneously, the effective discharge time t 0.9 The time required for the ceramic to release 90% of its energy is 63 ns, indicating that the ceramic can achieve efficient energy release in a very short time.

[0071] Example 4 This embodiment provides a method for preparing sodium bismuth titanate ceramic capacitor dielectric material. The main steps are similar to those in Embodiment 3, with the main difference being: Step S1: According to 0.9 (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)-0.1Sr0.7 Bi 0.2 Ca 0.1 Based on the stoichiometric ratio of the general chemical formula for TiO3, Bi2O3, TiO2, Nb2O5, Na2CO3, K2CO3, SrCO3, and CaCO3 were weighed and mixed evenly. The total mass of the raw materials was 10g, and an electronic balance with a weighing accuracy of 0.0001 was used. Since subsequent steps require a high-temperature sintering process, and bismuth is easily volatilized at high temperatures, an excess of 5% Bi2O3 was added during weighing.

[0072]

[0073] Example 5 This embodiment provides a sodium bismuth titanate ceramic capacitor dielectric material, with the general chemical formula (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3, in which x Take 0.12 ， The dielectric material of the sodium bismuth titanate ceramic capacitor is 0.88 (0.7Bi). 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)-0.12Sr 0.7 Bi 0.2 Ca 0.1 TiO3.

[0074] Example 6 This embodiment provides a sodium bismuth titanate ceramic capacitor dielectric material, with the general chemical formula (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3, in which x Take 0.18 ， The dielectric material of the sodium bismuth titanate ceramic capacitor is 0.82 (0.7Bi). 0.5 Na 0.5 TiO3-0.3K 0.5 Na0.5 NbO3)-0.18Sr 0.7 Bi 0.2 Ca 0.1 TiO3.

[0075] This invention is not limited to the above-described embodiments. If any modifications or variations to this invention do not depart from the spirit and scope of this invention, and if such modifications and variations fall within the scope of the claims and equivalent technologies of this invention, then this invention also intends to include such modifications and variations.

Claims

1. A dielectric material for sodium bismuth titanate ceramic capacitors, characterized in that: The general chemical formula of the dielectric material of the sodium bismuth titanate ceramic capacitor is (1- x (0.7Bi) 0.5 Na 0.5 TiO3-0.3K 0.5 Na 0.5 NbO3)- x Sr 0.7 Bi 0.2 Ca 0.1 TiO3, in which x The molar coefficient, x The value range is 0.1≤ x ≤0.

18.

2. A method for preparing the sodium bismuth titanate ceramic capacitor dielectric material according to claim 1, characterized in that, Includes the following steps: According to the stoichiometric ratio of the general chemical formula, weigh out Bi2O3, TiO2, Nb2O5, Na2CO3, K2CO3, SrCO3, and CaCO3 as raw materials and mix them evenly; The raw material is ball-milled once and then pre-calcined at high temperature to obtain pre-calcined powder. Then it is ball-milled a second time, and the pre-calcined powder after the second ball milling is granulated to obtain granulated powder. The granulated powder is dry-pressed to obtain an initial preform; The initial green body is debinded to obtain a ceramic green body; The ceramic preform after debinding is sintered to obtain sodium bismuth titanate ceramic capacitor dielectric material.

3. The method for preparing sodium bismuth titanate ceramic capacitor dielectric material according to claim 2, characterized in that: In the step of weighing and mixing Bi2O3, TiO2, Nb2O5, Na2CO3, K2CO3, SrCO3, and CaCO3 as raw materials according to the stoichiometric ratio of the general chemical formula, an excess of Bi2O3 is added during weighing.

4. The method for preparing sodium bismuth titanate ceramic capacitor dielectric material according to claim 2, characterized in that: In the process of ball milling the raw material once, pre-calcining the raw material obtained from the first ball milling at high temperature to obtain pre-calcined powder, ball milling the pre-calcined powder a second time, and granulating the pre-calcined powder after the second ball milling to obtain granulated powder, the raw material is weighed and put into a nylon ball milling jar during the first ball milling, and an appropriate amount of anhydrous ethanol and zirconium oxide beads of different particle sizes are added as grinding media for ball milling. When performing secondary ball milling on pre-calcined powder, the pre-calcined powder is put into a nylon ball mill jar, and an appropriate amount of anhydrous ethanol and zirconium oxide beads of different particle sizes are added as grinding media for ball milling.

5. The method for preparing sodium bismuth titanate ceramic capacitor dielectric material according to claim 2, characterized in that: In the process of ball milling the raw material once, pre-calcining the ball-milled raw material at high temperature to obtain pre-calcined powder, ball milling the pre-calcined powder a second time, and granulating the pre-calcined powder after the second ball milling to obtain granulated powder, the raw material pre-calcined at high temperature during the ball milling process is held at 800-900℃ for pre-calcination, and then cooled to room temperature after completion to obtain pre-calcined powder.

6. The method for preparing sodium bismuth titanate ceramic capacitor dielectric material according to claim 2, characterized in that: The raw material is ball-milled once, and the raw material from the first ball milling is pre-calcined at high temperature to obtain pre-calcined powder. The pre-calcined powder is then ball-milled a second time, and the pre-calcined powder after the second ball milling is granulated to obtain granulated powder. In the second ball milling process, an appropriate amount of binder is added to the pre-calcined powder that has undergone the second ball milling, and the powder is ground and then screened through a sieve to obtain granulated powder.

7. The method for preparing sodium bismuth titanate ceramic capacitor dielectric material according to claim 2, characterized in that: In the step of dry pressing granulated powder to obtain an initial preform, the granulated powder is weighed and placed in a mold, and pressure is applied in one direction to obtain the initial preform.

8. The method for preparing sodium bismuth titanate ceramic capacitor dielectric material according to claim 2, characterized in that: In the step of removing the binder from the initial green body to obtain the ceramic green body, the initial green body is heated to 300℃ and held at that temperature; then the temperature is raised from 300℃ to 550℃ and held at that temperature to obtain the ceramic green body.

9. The method for preparing sodium bismuth titanate ceramic capacitor dielectric material according to claim 2, characterized in that: In the step of sintering the debonded ceramic preform to obtain the sodium bismuth titanate ceramic capacitor dielectric material, the debonded ceramic preform is held at 1100-1180℃ with a heating rate controlled at 5-8℃ / min to obtain the sodium bismuth titanate ceramic capacitor dielectric material.

10. A ceramic capacitor, characterized in that: Includes the sodium bismuth titanate ceramic capacitor dielectric material as described in claim 1.

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