A donor and acceptor co-doped barium titanate system high-stability and high-breakdown field strength dielectric ceramic and a preparation method thereof

Abstract

This invention relates to a high-stability and high-breakdown-field-strength dielectric ceramic based on a donor-acceptor co-doped barium titanate system and its preparation method. The raw materials are prepared into powder according to the following composition and molar ratio: based on BaTiO3 as 100 mol%, 0.1–0.3 mol% Yb₂O₃ or Gd₂O₃, 4–7 mol% NaNbO₃ or KNbO₃, 2–5 mol% ZnO, and 0.4–0.8 mol% CaZrO₃ are added. The prepared powder is then ground and dried to obtain a pre-formed powder. PVA is added dropwise, mixed, and granulated to obtain a granulated powder. This granulated powder is then pressed, debinded, and sintered at high temperature to obtain a ceramic capacitor sample. The ceramic sample exhibits a single perovskite structure, and its temperature stability meets the X8R standard; the room-temperature relative permittivity ε r >4000; Breakthrough field strength E b With a voltage greater than 14kV / mm, it is a ceramic material with great application potential.

Description

Technical Field

[0001] This invention pertains to the preparation technology of dielectric ceramic materials, specifically a method for preparing barium titanate-based temperature-stable and high-breakdown-field-strength ceramics. In particular, it relates to a high-stability and high-breakdown-field-strength dielectric ceramic based on a donor-acceptor co-doped barium titanate system, and its preparation method. Background Technology

[0002] With the increasing integration and intelligence of electronic information technology, ceramic capacitors are facing demands for miniaturization, high dielectric constant and stability, and high insulation performance in various fields. Integration means an ever-expanding operating temperature range for capacitors. Based on market applications, Class II dielectric ceramic capacitors have been classified according to their temperature variation. Currently, the most commercially competitive product is the X7R capacitor, which, based on 25℃, exhibits a capacitance change rate of no more than ±15% within the range of -55℃ to 125℃. The X8R capacitor, with even higher requirements for temperature stability (-55~+150℃, |ΔC / C...),... 25℃ Capacitors with a breakdown voltage of ≤±15% are also attracting significant attention. Furthermore, with the development of electronic information technology, small-sized ceramic capacitors require higher breakdown field strengths, but high breakdown field strength and high dielectric constant are mutually coupled. Therefore, it is essential to develop temperature-stable ceramic capacitors that simultaneously possess both high breakdown field strength and high dielectric constant.

[0003] Barium titanate (BaTiO3) has advantages such as high production volume, mature processing, high dielectric constant, and moderate Curie temperature. It has long been the most widely used high-dielectric ceramic material. However, pure BaTiO3 is a ferroelectric phase, with a capacitance-temperature change rate greater than 50% in the operating temperature range, exhibiting extremely poor temperature stability and low breakdown field strength. This poor temperature stability causes BaTiO3 ceramic capacitors to fail in extreme environments, further limiting its applications. Therefore, modification with different elements / compositions is necessary. The high temperature stability and high breakdown strength of ferroelectrics require transformation into a relaxor ferroelectric phase. Phase transitions are suppressed through thermal fluctuations, compositional fluctuations, structural fluctuations, and stress fluctuations. The domain structure transforms from ordered to disordered, and the phase transition process changes from an abrupt process to a continuous relaxation process, resulting in a lower and broader Curie peak, while simultaneously improving voltage withstand performance.

[0004] To ensure its dielectric constant, elements with low solid solubility in the BaTiO3 lattice, such as rare earth elements, can be introduced to form a core-shell structure. These elements have low solubility and slow diffusion rates in the BaTiO3 lattice, accumulating in large quantities in the outer layer of the grains. This preserves the ferroelectric core phase with high Curie temperature and high dielectric constant, while the outer layer is a relaxor ferroelectric shell phase with low Curie temperature. The capacitance-temperature curve of the core-shell structure typically exhibits two Curie peaks, corresponding to the core phase (high temperature) and the shell phase (low temperature), respectively. This characteristic also broadens the temperature stability range of BaTiO3-based ceramic capacitors. However, ions that readily form core-shell structures usually have different valences and ionic radii than the ions at the A and B sites in the BaTiO3 crystal structure. When these ions enter the BaTiO3 lattice, they create point defects, leading to an increase in charge carriers and a significant decrease in the ceramic breakdown field strength. To address this issue and obtain BaTiO3-based ceramic capacitors with high breakdown field strength and temperature stability, this invention employs a donor-acceptor co-doping scheme. This neutralizes the charge mismatch caused by single-element doping, thereby increasing the breakdown field strength. Simultaneously, co-doping helps to further enhance the solid solubility of the dopant element in the BaTiO3 lattice, preserving the high dielectric constant nucleus to a greater extent and improving the dielectric constant at high temperatures, thus achieving the X8R standard. Summary of the Invention

[0005] The purpose of this invention is to modify barium titanate material by co-doping with donors (trivalent gadolinium ions, trivalent ytterbium ions, or pentavalent niobium ions) and acceptors (monovalent sodium ions or monovalent potassium ions), while adding other additives (zirconia and zinc oxide) to form a formulation system. This process involves high-temperature solid-state reaction sintering to prepare dielectric ceramics with wide temperature stability, high breakdown field strength, and high dielectric constant. This provides a simple, low-cost, and high-performance method for preparing ceramic capacitor materials.

[0006] This invention is achieved through the following technical solution:

[0007] A high-stability and high-breakdown-field-strength dielectric ceramic based on a donor-acceptor co-doped barium titanate system, wherein the ceramic formulation comprises, based on 100 mol% BaTiO3:

[0008]

[0009] The present invention discloses a method for preparing a high-stability and high-breakdown-field-strength dielectric ceramic based on a donor-acceptor co-doped barium titanate system, comprising the following steps:

[0010] (1) Preparation of ceramic powder: Prepare the powder according to the composition and molar ratio of the raw materials: based on BaTiO3 as 100mol%, add 0.1-0.3mol% Yb2O3 or Gd2O3, 4-7mol% NaNbO3 or KNbO3, 2-5mol% ZnO, and 0.4-0.8mol% CaZrO3. The prepared powder is ground and mixed using anhydrous ethanol as the grinding medium. After drying, it is passed through a 30-100 mesh sieve to obtain a uniformly mixed pre-prepared powder.

[0011] (2) Powder granulation and green body forming: PVA aqueous solution with a content of 5-10% by mass is added dropwise to the pre-made powder obtained in step (1), and the amount added is 6-8% of the powder mass ratio. The PVA solution and powder are mixed evenly by dropwise addition, and then granulated by grinding to obtain granulated powder. The obtained granulated powder is pressed and formed by the dry molding method of electronic ceramics. The formed ceramic green body is heated to 400-800℃ and kept at the temperature for 0.5-1h for debinding.

[0012] (3) Sintering of ceramics: The ceramic blank after debinding in step (2) is sintered at high temperature to obtain ceramic capacitor samples.

[0013] In step (1), the grinding and mixing are carried out using a planetary ball mill, with a grinding time of 4-6 hours and a rotation speed of 350-400 r / min.

[0014] In step (2), the pressure applied by the dry forming method is 200MPa-400MPa, resulting in a circular blank.

[0015] In step (3), the sintering temperature is 1160℃-1180℃. During the heating process, the heating rate is 3-5℃ / min when the temperature is less than or equal to 1000℃ and 1-2℃ / min when the temperature is greater than 1000℃. After holding at the sintering temperature for 1.5-2.5h, the furnace is cooled.

[0016] The raw materials include

[0017] BaTiO3 (base material, 100 mol%)

[0018] Donors: Gd₂O₃, Yb₂O₃ (addition amount: 0.1–0.3 mol%)

[0019] Acceptors: NaNbO3, KNbO3 (added at 4-7 mol%)

[0020] Other additives include CaZrO3 (0.4–0.8 mol%) and ZnO (2–5 mol%). This ceramic capacitor has a single perovskite structure.

[0021] The chemical composition, microstructure, temperature stability, and breakdown field strength of the BaTiO3-based ceramic capacitor obtained in this invention were characterized and tested. It was found that the ceramic sample has a single perovskite structure with uniform grain size distribution, and its temperature stability meets the X8R standard. The room temperature relative permittivity ε... r >4000; room temperature dielectric loss tanδ approximately 1.00%; volume resistivity ρ v >10 12 Ω·cm, breakdown field strength E b With a voltage greater than 14kV / mm, it is a ceramic material with high temperature stability, high breakdown field strength, and great application potential.

[0022] In summary, this invention provides a method for preparing barium titanate-based temperature-stable and high-breakdown-field-strength ceramics. The donor-acceptor co-doping of core-shell BaTiO3-based ceramics neutralizes the charge mismatch caused by single-element doping, resulting in significantly improved temperature stability and breakdown field strength compared to traditional single-doped core-shell BaTiO3-based ceramics. The synthesized samples exhibit a capacitance-temperature change rate within -15% to +15% in the temperature range of -55℃ to 150℃, meeting the requirements of X8R capacitors. Furthermore, the defects generated at the A-site and B-site by some of the dopant ions, as well as the large-area core phase structure, further enhance the dielectric constant of the BaTiO3-based ceramics; the relative permittivity of the prepared samples exceeds 4000 at room temperature. This invention is simple to operate, has a short preparation cycle, low cost, and produces BaTiO3-based ceramics with uniform microstructure and excellent temperature stability and high breakdown field strength. Attached Figure Description

[0023] Figure 1 The X-ray diffraction (XRD) images of the dielectric ceramic capacitor samples prepared in Examples 1-4 show that the ceramic sample has a single perovskite structure. After sintering, all samples are well calibrated with the PDF card and have no impurities. The phase transformation of the ceramic can be observed with the help of XRD.

[0024] Figure 2 The images are scanning electron microscope (SEM) images of the dielectric ceramic capacitor samples prepared in Examples 1-4, showing that the ceramic samples have a uniform fine-grained structure with grain sizes between 0.3-0.6 nm. SEM can be used to observe the microstructure and sintering density of ceramics.

[0025] Figure 3 These are the dielectric constant / dielectric loss-temperature curves of the ceramic capacitor samples prepared in Examples 1-4. The dielectric constant is greater than 4000, the loss is less than 2%, and the temperature stability meets X8R. Detailed Implementation

[0026] Example 1:

[0027] (1) Preparation of ceramic powder: The raw materials were prepared according to the composition of the ceramic capacitor, with the following composition: BaTiO3-0.10mol%Gd2O3-4mol%NaNbO3-3.5mol%ZnO-0.65mol%CaZrO3. 30g BaTiO3, 0.047g Gd2O3, 0.84g NaNbO3, 0.37g ZnO, and 0.15g CaZrO3 were weighed out respectively. The prepared powder was thoroughly ground and mixed using anhydrous ethanol as the grinding medium, dried, and then passed through a 30-mesh sieve to obtain a uniformly mixed raw material.

[0028] (2) Powder granulation and green body forming: Add 8% PVA aqueous solution by mass to the pre-formed powder obtained in step (1), the amount added being 6% of the powder by mass. Mix the PVA solution and powder evenly by drop addition, and granulate thoroughly to obtain the pre-formed powder. Load the pre-formed powder into a circular pressing mold, apply a pressure of 200 MPa using a pressing machine and hold the pressure for a period of time to obtain a circular ceramic green body. Heat the ceramic green body to 600℃ at a heating rate of 1℃ / min and hold for 0.5 hours to remove the binder and water from the green body, and then allow it to cool naturally to room temperature.

[0029] (3) Sintering of ceramics: The ceramic blank after debinding in step (2) was heated to 1000℃ at a heating rate of 5℃ / min, and then heated to 1160℃ at a heating rate of 2℃ / min. The sample was sintered at this temperature for 2 hours, and then naturally cooled to room temperature to obtain a BaTiO3-based ceramic capacitor sample. The phase structure of the synthesized sample is shown in the attached figure. Figure 1 As shown, the structure is a single perovskite with no other impurities. Significant dispersion occurs on the (101) and (110) crystal planes near 31°, the (002) and (200) crystal planes near 45°, and the (112) and (211) crystal planes near 56°, indicating that the synthesized sample has transformed from a ferroelectric to a relaxor ferroelectric. The morphology and structure are shown in the attached figure. Figure 2 As shown, the average grain size is 0.48 μm. The internal stress of the fine-grained structure is beneficial to improving temperature stability. Simultaneously, the larger proportion of grain boundaries reduces the probability of grain breakdown, thereby increasing the breakdown field strength, and the insulation performance of the sample is also optimized. Dielectric performance test results are attached. Figure 3 As shown, the temperature stability meets the X8R requirements, the dielectric constant is greater than 4000 at room temperature, and the loss is less than 2% throughout the entire test range, with a room temperature loss of around 1.00%. The dielectric constants of the ceramic capacitors all exhibit double Curie peaks, indicating that the samples have formed a core-shell structure. The insulation performance is shown in Appendix Table 1, with a breakdown field strength reaching 18.0 kV / mm.

[0030] Example 2:

[0031] (1) Preparation of ceramic powder: The raw materials were prepared according to the composition of the ceramic capacitor. The raw materials were prepared according to the following composition: BaTiO3-0.2mol% Gd2O3-5mol% KNbO3-2mol% ZnO-0.4mol% CaZrO3. 30g BaTiO3, 0.093g Gd2O3, 1.16g KNbO3, 0.21g ZnO and 0.092g CaZrO3 were weighed out respectively. The prepared powder was thoroughly ground and mixed using anhydrous ethanol as the grinding medium. After drying, it was passed through a 50-mesh sieve to obtain a uniformly mixed raw material.

[0032] (2) Powder granulation and green body forming: Add 8% PVA aqueous solution by mass to the pre-formed powder obtained in step (1), the amount added being 7% of the powder by mass. Mix the PVA solution and powder evenly by drop addition, and granulate thoroughly to obtain the pre-formed powder. Load the pre-formed powder into a circular pressing mold, apply a pressure of 300 MPa using a pressing machine and hold the pressure for a period of time to obtain a circular ceramic green body. Heat the ceramic green body to 600℃ at a heating rate of 1℃ / min and hold for 0.5 hours to remove the binder, so as to remove the water and binder from the green body, and then let it cool naturally to room temperature.

[0033] (3) Sintering of ceramics: The ceramic blank after debinding in step (2) was heated to 1000℃ at a heating rate of 5℃ / min, and then heated to 1170℃ at a heating rate of 2℃ / min. The sample was sintered at this temperature for 1.5 h, and then naturally cooled to room temperature to obtain a BaTiO3-based ceramic capacitor sample. The phase structure of the synthesized sample is shown in the attached figure. Figure 1 As shown, the structure is a single perovskite with no other impurities. Significant dispersion occurs on the (101) and (110) crystal planes near 31°, the (002) and (200) crystal planes near 45°, and the (112) and (211) crystal planes near 56°, indicating that the synthesized sample has transformed from a ferroelectric to a relaxor ferroelectric. The morphology and structure are shown in the attached figure. Figure 2 As shown, the average grain size is 0.46 μm. The fine-grained structure significantly improves the temperature stability and breakdown field strength of the sample, and its insulation performance is also optimized. Dielectric performance test results are attached. Figure 3 As shown, the temperature stability meets the X8R requirements, the dielectric constant is greater than 4000 at room temperature, and the loss is less than 2% throughout the entire test range, with a room temperature loss of around 1.00%. The dielectric constants of the ceramic capacitors all exhibit double Curie peaks, indicating that the samples have formed a core-shell structure. The insulation performance is shown in Appendix Table 1, with a breakdown field strength reaching 17.0 kV / mm.

[0034] Example 3:

[0035] (1) Preparation of ceramic powder: The raw materials were prepared according to the composition of the ceramic capacitor. The raw materials were prepared according to the following composition: BaTiO3-0.25mol%Yb2O3-6mol%NaNbO3-4mol%ZnO-0.6mol%CaZrO3. 30g BaTiO3, 0.13g Yb2O3, 1.27g NaNbO3, 0.42g ZnO and 0.14g CaZrO3 were weighed out respectively. The prepared powder was thoroughly ground and mixed using anhydrous ethanol as the grinding medium. After drying, it was passed through a 50-mesh sieve to obtain a uniformly mixed raw material.

[0036] (2) Granulation and molding of ceramic powder: PVA aqueous solution with a content of 8% by mass is added dropwise to the pre-formed powder obtained in step (1), the amount added being 7% of the powder mass ratio. The PVA solution and powder are mixed evenly by dropwise addition, and then granulated by thorough grinding to obtain pre-formed powder. The pre-formed powder is loaded into a circular pressing mold, and a pressure of 350MPa is applied using a pressing machine and the pressure is held for a sufficient period of time to obtain a circular ceramic blank. The ceramic blank is heated to 600℃ at a heating rate of 1℃ / min and held at that temperature for 1 hour to remove the binder, so as to remove the water and binder from the blank, and then naturally cooled to room temperature.

[0037] (3) Sintering of ceramics: The ceramic blank after debinding in step (2) was heated to 1000℃ at a heating rate of 5℃ / min, and then heated to 1170℃ at a heating rate of 2℃ / min. The sample was sintered at this temperature for 2.5 h, and then naturally cooled to room temperature to obtain BaTiO3-based ceramic capacitor samples. The phase structure of the synthesized samples is shown in the attached figure. Figure 1 As shown, the structure is a single perovskite with no other impurities. Significant dispersion occurs on the (101) and (110) crystal planes near 31°, the (002) and (200) crystal planes near 45°, and the (112) and (211) crystal planes near 56°, indicating that the synthesized sample has transformed from a ferroelectric to a relaxor ferroelectric. The morphology and structure are shown in the attached figure. Figure 2 As shown, the average grain size is 0.43 μm. Thanks to the internal stress and high grain boundary density of the fine grains, the temperature stability and breakdown field strength of the sample are optimized, and the insulation performance is also improved. The dielectric performance test results are attached. Figure 3 As shown, the temperature stability meets the X8R requirements, the dielectric constant is greater than 4000 at room temperature, and the loss is less than 2% throughout the entire test range, with a room temperature loss of around 1.00%. The dielectric constants of the ceramic capacitors all exhibit double Curie peaks, indicating that the samples have formed a core-shell structure. The insulation performance is shown in Appendix Table 1, with a breakdown field strength reaching 15.8 kV / mm.

[0038] Example 4:

[0039] (1) Preparation of ceramic powder: The raw materials were prepared according to the composition of the ceramic capacitor. The raw materials were prepared according to the following composition: BaTiO3-0.3mol%Yb2O3-7mol%KNbO3-5mol%ZnO-0.8mol%CaZrO3. 30g BaTiO3, 0.15g Yb2O3, 1.62g KNbO3, 0.52g ZnO and 0.18g CaZrO3 were weighed out respectively. The prepared powder was thoroughly ground and mixed using anhydrous ethanol as the grinding medium. After drying, it was passed through a 100-mesh sieve to obtain a uniformly mixed raw material.

[0040] (2) Powder granulation and green body forming: Add 8% PVA aqueous solution by mass to the pre-formed powder obtained in step (1), the amount added being 8% of the powder mass ratio. Mix the PVA solution and powder evenly by drop addition, and granulate thoroughly to obtain the pre-formed powder. Load the pre-formed powder into a circular pressing mold, apply a pressure of 400MPa using a pressing machine and hold the pressure for a period of time to obtain a circular ceramic green body. Heat the ceramic green body to 600℃ at a heating rate of 1℃ / min and hold for 1 hour to remove the binder, so as to remove the water and binder from the green body, and then let it cool naturally to room temperature.

[0041] (3) Sintering of ceramics: The ceramic blank after debinding in step (2) was heated to 1000℃ at a heating rate of 5℃ / min, and then heated to 1180℃ at a heating rate of 2℃ / min. It was then sintered at this temperature for 2.5 h to allow the reaction to proceed, and then naturally cooled to room temperature to obtain BaTiO3-based ceramic capacitors. The morphology and structure are shown in the attached figure. Figure 2 As shown, the average grain size is 0.41 μm. The fine grains and high grain boundary density improve the temperature stability and breakdown field strength of the sample, and also optimize the insulation performance. Dielectric property test results are attached. Figure 3 As shown, the temperature stability meets the X8R requirements, the dielectric constant is greater than 4000 at room temperature, and the loss is less than 2% throughout the entire test range, with a room temperature loss of around 1.00%. The dielectric constants of the ceramic capacitors all exhibit double Curie peaks, indicating that the samples have formed a core-shell structure. The insulation performance is shown in Appendix Table 1, with a breakdown field strength reaching 16.2 kV / mm.

[0042] Table 1 Insulation performance of Examples 1 to 4

[0043]

[0044] Appendix Table 1 shows the insulation performance of Examples 1 to 4, with dielectric loss tanδ < 1% and volume resistivity ρ. v More than 10 12 Ω·cm. Breakdown field strength E b>15kV / mm. The above examples demonstrate the capacitance-temperature stability and breakdown field strength of this BaTiO3-based ceramic capacitor.

[0045] The preparation technology of this invention differs from others in that BaTiO3-based ceramics achieve an X8R standard while possessing a dielectric constant of over 4000 and a breakdown field strength exceeding 15kV / mm. Compared to other X8R capacitors, it exhibits a higher dielectric constant and superior insulation performance. The process is simple, and the raw material cost is low, making it an ideal temperature-stable capacitor material. This invention has been preferably described through examples. Those skilled in the art can clearly modify or appropriately alter and combine the technical methods described herein without departing from the content, spirit, and scope of this invention to achieve the technology of this invention. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A high-stability and high-breakdown-field-strength dielectric ceramic based on a donor-acceptor co-doped barium titanate system, characterized in that, The dielectric ceramic formulation consists of BaTiO3 at 100 mol% as follows: BaTiO3 100mol% Yb₂O₃ or Gd₂O₃ 0.1~0.3 mol% 4~7 mol% NaNbO3 or KNbO3 ZnO 2~5 mol% CaZrO3 0.4~0.8 mol% The ceramic has a single perovskite structure with uniform grain size distribution, and its capacitance-temperature stability meets the X8R standard; the room temperature relative permittivity ε r >4000; room temperature dielectric loss tanδ approximately 1.00%; volume resistivity ρ v >10 12 Ω·cm, breakdown field strength E b >14kV / mm.

2. The method for preparing a high-stability and high-breakdown-field-strength dielectric ceramic of a donor-acceptor co-doped barium titanate system as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of ceramic powder: Prepare the powder according to the composition and molar ratio of the raw materials: with BaTiO3 as 100mol%, add 0.1~0.3mol% Yb2O3 or Gd2O3, 4~7mol% NaNbO3 or KNbO3, 2~5mol% ZnO, and 0.4~0.8mol% CaZrO3. The prepared powder is ground and mixed using anhydrous ethanol as the grinding medium. After drying, it is passed through a 30-100 mesh sieve to obtain a uniformly mixed pre-prepared powder. (2) Powder granulation and green body forming: Add 5-10% PVA aqueous solution by mass to the pre-made powder obtained in step (1), the amount added is 6-8% of the powder mass ratio, and mix the PVA solution and powder evenly by adding dropwise. Grind and granulate to obtain granulated powder. Press the obtained granulated powder into shape using the dry molding method of electronic ceramics. Heat the shaped ceramic green body to 400-800℃ and keep it at that temperature for 0.5-1h to remove the glue. (3) Sintering of ceramics: The ceramic blank after debinding in step (2) is sintered at high temperature to obtain ceramic capacitor samples.

3. The preparation method according to claim 2, characterized in that, In step (1), a planetary ball mill is used for grinding and mixing. The grinding time is 4-6 hours and the rotation speed is 350-400 r / min.

4. The preparation method according to claim 2, characterized in that, In step (2), the pressure applied by the dry forming method is 200MPa-400MPa, resulting in a circular blank.

5. The preparation method according to claim 2, characterized in that, In step (3), the sintering temperature is 1160℃-1180℃. During the heating process, the heating rate is 3-5℃ / min when the temperature is less than or equal to 1000℃ and 1-2℃ / min when the temperature is greater than 1000℃. After holding at the sintering temperature for 1.5-2.5h, the furnace is cooled.

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