A dc bias characteristic x7r ceramic dielectric material and a method for preparing the same

Abstract

The application discloses a DC bias characteristic X7R ceramic dielectric material and a preparation method thereof. A uniform core-shell structure barium titanate main crystal phase is constructed through an optimized two-step in-situ hydrothermal process, high-purity nano BaTiO3 is used as the core, Dy3+ doped BaTiO3 is used as the shell, rare earth-transition metal multi-element doping, a compounded glass phase and a segmented atmosphere sintering process are combined, the micro mechanism of the core-shell structure for inhibiting ferroelectric domain flipping is determined, the design logic and effect of the optimization process are determined, and technical problems such as uneven dispersion, homogeneous nucleation and residual impurities in the preparation of a traditional X7R ceramic core-shell structure are solved. The prepared X7R ceramic material has high bias stability, wide temperature stability and high reliability, and has extremely high engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of electronic functional ceramics technology, specifically relating to a DC bias characteristic X7R ceramic dielectric material and its preparation method. Background Technology

[0002] X7R ceramic dielectric material is one of the most widely used dielectric materials in the MLCC field. According to EIA standards, it must meet the requirement of a mass change rate of ≤±15% over a wide temperature range of -55℃ to 125℃, while also possessing suitable dielectric constant, low dielectric loss, and high insulation resistivity. It is widely used in high-end applications such as automotive electronics, industrial control, and communication base stations. As MLCCs upgrade towards ultra-thin dielectrics, miniaturization, and high voltage withstand, the DC electric field strength during device operation has increased significantly, making the inherent defects of traditional barium titanate-based X7R ceramics increasingly prominent.

[0003] Barium titanate, as a typical ferroelectric material, undergoes forced flipping of its intracrystalline ferroelectric domains under DC bias, leading to a sharp decay in its dielectric constant. Conventional X7R ceramics exhibit a capacitance decay rate as high as 15% to 40% under rated DC bias, severely impacting circuit stability. Existing modification techniques mostly employ single rare-earth doping or single glass phase additives, which can only locally optimize temperature drift characteristics and cannot simultaneously suppress ferroelectric domain flipping or repair grain boundary defects, resulting in limited improvement in DC bias stability. Some techniques attempt to introduce core-shell structures to improve bias performance, but these suffer from problems such as uneven core-shell coating, shell detachment, and impure crystal phases. Furthermore, the traditional one-step sintering process easily leads to abnormal grain growth and low density, further exacerbating dielectric loss and capacitance drift under bias. Moreover, the sintering temperature is generally higher than 1320℃, resulting in high energy consumption and poor compatibility with base metal electrodes.

[0004] Currently, while existing publicly available technologies attempt to improve bias characteristics through doping modification, they generally suffer from problems such as a single doping system, insufficient control over crystal phase structure, ambiguous core-shell structure construction, and poor process compatibility. These limitations prevent the synergistic optimization of achieving wide-temperature capacitance variation and low loss, making it difficult to meet the stringent performance requirements of high-end MLCCs. Therefore, developing X7R ceramic dielectric materials with excellent DC bias characteristics to overcome existing technological bottlenecks has significant engineering value and market implications. Summary of the Invention

[0005] This invention provides a DC bias-controlled X7R ceramic dielectric material and its preparation method, addressing the technical shortcomings of existing X7R ceramic dielectric materials, such as insufficient wide-temperature dielectric stability under DC bias, poor grain uniformity, and unclear core-shell structure. By employing an in-situ hydrothermal method to prepare a uniform core-shell structured barium titanate main crystal phase, a multi-component synergistic doping system, and a segmented atmosphere sintering process, the microscopic construction principle and bias stabilization mechanism of the core-shell structure are clarified. This achieves comprehensive optimization of DC bias stability, wide-temperature capacitive variation, dielectric loss, and sintering activity, filling the technological gap in high-bias-controlled stable X7R materials for high-end MLCCs.

[0006] In a first aspect, the present invention relates to an X7R ceramic dielectric material with DC bias characteristics, which, by mass percentage, comprises the following components: The core-shell structured barium titanate powder prepared by in-situ hydrothermal method contains 96.0%~97.5% rare earth composite dopant, 0.8%~1.5% transition metal oxide dopant, 0.3%~0.6% composite glass phase additive, 1.2%~2.0% composite glass phase additive, and 0.2%~0.5% sintering aid; the sum of the contents of the above components is 100%. The core-shell structured barium titanate powder has a core phase of high-purity BaTiO3 with a purity ≥99.9% and a particle size of 50~80nm, and a shell phase of Dy3+-doped BaTiO3 with a doping amount of 0.3%~0.8wt%. The shell layer thickness is 5~10nm, and the coating uniformity is ≥98%. The rare earth composite dopant is a mixture of Ho2O3 and Dy2O3 in a mass ratio of 1:0.6 to 1:1.2; the transition metal oxide dopant is a mixture of Nb2O5 and Ta2O5 in a mass ratio of 1:0.4 to 1:0.8; the composite glass phase aid is a mixture of borosilicate glass and zinc borosilicate glass in a mass ratio of 1:0.5 to 1:1; and the sintering aid is a mixture of SrCO3 and Al2O3.

[0007] Barium titanate powder with a core-shell structure: 96.0%~97.5%, serving as the core functional phase. The core phase is high-purity BaTiO3 (purity ≥99.9%, particle size 50~80nm; excessively small particle size can easily lead to abnormal growth during sintering, while excessively large particle size reduces the uniformity of dielectric constant); the shell phase is Dy3+-doped BaTiO3 (doping amount 0.3%~0.8wt%, shell thickness 5~10nm). If the shell is too thin, it cannot form ferroelectric domain barriers; if it is too thick, it will reduce the overall dielectric constant. This thickness range can balance bias voltage stability and dielectric performance; the core-shell coating uniformity is ≥98%, with no bare core or shell agglomeration.

[0008] Rare earth composite dopant: 0.8%~1.5%, composed of holmium oxide (Ho2O3) and dysprosium oxide (Dy2O3) in a mass ratio of 1:0.6~1:1.2. The ionic radii of Ho3+ and Dy3+ are compatible with the A-site of BaTiO3, and synergistic doping can precisely control the degree of lattice distortion. This compound ratio can achieve a capacitive variation rate of ≤±11% from -55℃ to 125℃.

[0009] Transition metal oxide dopants: 0.3%~0.6%, composed of niobium pentoxide (Nb₂O₅) and tantalum pentoxide (Ta₂O₅) in a mass ratio of 1:0.4~1:0.8. Nb⁵⁺ and Ta⁵⁺ are high-valence donor dopants, which can fill oxygen vacancies and enhance grain boundary barriers. Excessive doping will reduce density, while insufficient doping will result in poor defect repair.

[0010] Composite glass phase additive: 1.2%~2.0%, composed of borosilicate glass and zinc borosilicate glass in a mass ratio of 1:0.5~1:1. Borosilicate glass optimizes grain boundary bonding strength, while zinc borosilicate glass lowers the sintering liquid phase formation temperature. The combination of the two can reduce the sintering temperature to 1240~1280℃, avoiding the grain boundary embrittlement problem caused by a single glass.

[0011] Sintering aid: 0.2%~0.5%, a mixture of strontium carbonate (SrCO3) and alumina (Al2O3). Sr2+ doping inhibits the radial growth of BaTiO3 grains, while Al2O3 refines the grains, working together to control the grain size within 150~250nm, thereby improving the ceramic density and bias stability.

[0012] Secondly, the present invention relates to a method for preparing the X7R ceramic dielectric material with DC bias characteristics, characterized by comprising two stages: pre-preparation of core-shell structured barium titanate and ceramic sintering, the specific steps of which are as follows: (1) Preparation of core-shell structured barium titanate powder Core phase synthesis: Using barium carbonate and titanium dioxide as raw materials, high-purity BaTiO3 core phase powder with a purity ≥99.9% and a particle size of 50~80nm was obtained by hydrothermal method; Shell coating: Pre-activation treatment: Disperse the core phase powder in an ethanol-water mixed solvent, add 0.1~0.2wt% ammonium polyacrylate as a dispersant, and ultrasonically vibrate for 30~50min to form a highly dispersed suspension; Gradient dropwise control: Prepare a mixed precursor solution of dysprosium nitrate, barium carbonate and tetrabutyl titanate according to the shell doping amount. Use a dual-feed system to dropwise the core phase suspension and NaOH alkaline solution with pH=13~13.5 at a rate of 0.4~0.6 mL / min. Maintain the pH of the reaction system at 12~13 throughout the process and control the temperature at 40~50℃. Hydrothermal crystallization: The mixed slurry is transferred into a hydrothermal reactor, first heated to 100-120℃ at 1-3℃ / min and held for 1-2 hours; then heated to 140-160℃ at 2-5℃ / min and held for 4-6 hours to complete the in-situ growth of the Dy3+ doped BaTiO3 shell. Post-processing enhancement: After the reaction was completed, the powder was washed by centrifugation with deionized water and anhydrous ethanol, then washed by centrifugation with dilute acetic acid, and vacuum dried to obtain core-shell structured barium titanate powder. (2) Preparation of ceramic dielectric materials Powder premixing and wet ball milling: Weigh each component according to the formula, add deionized water and ammonium polyacrylate dispersant, ball-to-material ratio 3:1~5:1, speed 300~400r / min, ball mill for 8~12h to obtain a uniform slurry; Segmented pre-calcination: After spray drying and granulation of the slurry, it is pre-calcined in segments at 450~500℃ for 2~3 hours and 850~900℃ for 3~4 hours to obtain pre-calcined powder; Dry pressing: Add polyvinyl alcohol binder to the pre-fired powder, dry press at 80~120MPa pressure, hold pressure for 30~60s to obtain green body; Segmented atmosphere sintering: The green body is held at 550~620℃ for debinding, held at 1050~1100℃ for densification, held at 1240~1280℃ for crystallization, and then rapidly cooled in the furnace to obtain the finished product.

[0013] Preferably, in the nucleus phase synthesis step, barium carbonate and titanium dioxide are dissolved in deionized water at a molar ratio of 1:1.005, ammonia is added to adjust the pH to 10-11, the mixture is transferred to a hydrothermal reactor, kept at 180-200℃ for 8-10 hours, centrifuged, washed, and vacuum dried to obtain high-purity BaTiO3 nucleus phase powder with a purity ≥99.9% and a particle size of 50-80nm.

[0014] Preferably, the post-treatment enhancement involves washing the product by centrifugation three times each with deionized water and anhydrous ethanol after the reaction, followed by washing it once with dilute acetic acid. The product is then vacuum dried to obtain core-shell structured barium titanate powder with a shell thickness of 5-10 nm.

[0015] Preferably, the spray drying granulation has an inlet air temperature of 180~200℃ and an outlet air temperature of 90~100℃.

[0016] Preferably, the segmented atmosphere sintering includes: slowly heating to 550-620°C at a rate of 3-5°C / min, holding at that temperature for 1-2 hours, and completely removing the polyvinyl alcohol binder; Low-temperature densification stage: Continue to raise the temperature to 1050~1100℃ at a rate of 2~3℃ / min, and hold for 2~3 hours to achieve initial densification; High-temperature crystallization stage: slowly raise the temperature to 1240~1280℃ at a rate of 1~2℃ / min, hold for 3~4 hours, and introduce a nitrogen-oxygen mixed atmosphere with an oxygen volume fraction of 5%~8%. Temperature control and cooling stage: rapidly cool down to 850~900℃ at a rate of 4~6℃ / min, and then cool down to room temperature with the furnace.

[0017] Core-shell structured barium titanate was prepared using a two-step in-situ hydrothermal process. The process was optimized through four steps: pre-activation, gradient addition, two-stage temperature-increasing crystallization, and post-treatment strengthening, ensuring uniform shell coating, intact core-shell structure, and absence of impurity phases. The specific steps are as follows: Preparation of nucleus phase powder: Barium carbonate (BaCO3) and titanium dioxide (TiO2) were dissolved in deionized water at a molar ratio of 1:1.005. Ammonia was added to adjust the pH to 10-11. The mixture was then transferred to a hydrothermal reactor and kept at 180-200℃ for 8-10 hours. After centrifugation, washing, and vacuum drying, high-purity BaTiO3 nucleus phase powder with a purity ≥99.9% and a particle size of 50-80 nm was obtained.

[0018] Pre-activation treatment: Disperse the core phase powder in an ethanol-water mixed solvent (volume ratio 1:1), add 0.1~0.2wt% wt% ammonium polyacrylate as a dispersant, and ultrasonically vibrate for 30~50 min to form a highly dispersed suspension, ensuring that the core phase particles are monodispersed and providing a substrate for uniform shell growth.

[0019] Gradient dropwise control: Prepare a mixed precursor solution of dysprosium nitrate, barium carbonate and tetrabutyl titanate according to the shell doping amount. Use a dual-feed system to dropwise the nucleus suspension and NaOH alkaline solution with pH=13~13.5 at a rate of 0.4~0.6mL / min. Maintain the pH of the reaction system at 12~13 throughout the process and control the temperature at 40~50℃ to avoid local supersaturation that may lead to homogeneous nucleation and ensure directional growth of the shell.

[0020] Hydrothermal crystallization: A two-stage heating process is adopted—first, the temperature is increased to 100-120℃ at a rate of 1-3℃ / min and held for 1-2 hours to promote the adsorption and spreading of the precursor on the surface of the nucleus phase; then, the temperature is increased to 140-160℃ at a rate of 2-5℃ / min and held for 4-6 hours to complete the in-situ growth of the Dy3+ doped BaTiO3 shell, thereby improving the bonding force and crystallinity between the shell and the nucleus phase.

[0021] The post-treatment enhancement process is as follows: After the reaction is completed, the powder is washed three times each with deionized water and anhydrous ethanol by centrifugation, and then washed once with dilute acetic acid by centrifugation. The powder is then vacuum dried to obtain core-shell structured barium titanate powder with a shell thickness of 5-10 nm, uniform coating without damage or impurities.

[0022] The entire process of core-shell powder pre-preparation, wet ball milling and mixing, segmented pre-firing, dry pressing and segmented atmosphere sintering is adopted to preserve the integrity of the core-shell structure. The specific steps are as follows: Powder premixing and wet ball milling: Weigh the self-made core-shell structured barium titanate powder, rare earth composite dopant, transition metal oxide dopant, composite glass phase additive and sintering aid according to the formula ratio, add deionized water and dispersant (ammonium polyacrylate, the amount added is 0.5%~0.8% of the total mass of powder), place in a planetary ball mill, ball-to-powder ratio of 3:1~5:1, speed of 300~400 r / min, ball mill for 8~12 h; low-speed ball milling is used to avoid core-shell structure breakage, and a uniformly dispersed slurry without agglomeration is obtained.

[0023] Segmented pre-calcination treatment: The ball-milled slurry is spray-dried and granulated (inlet air temperature 180~200℃, outlet air temperature 90~100℃) to obtain granulated powder with good flowability; then the granulated powder is placed in a muffle furnace for segmented pre-calcination: the first stage is held at 450~500℃ for 2~3h to slowly remove organic impurities and residual solvents and avoid rapid heating that could cause the core-shell structure to crack; the second stage is held at 850~900℃ for 3~4h to complete the solid-phase reaction and preliminary crystallization. After pre-calcination, the particle size uniformity of the powder is ≥95% and the core-shell structure remains intact.

[0024] Dry pressing: Add a binder (polyvinyl alcohol, 1.0%~1.5wt%) to the pre-fired powder, granulate it twice, and then dry press it with a pressing pressure of 80~120MPa and a holding pressure of 30~60s. Static pressing is used to avoid damage to the core-shell structure by shear force, and a green body with uniform density is obtained.

[0025] Segmented atmosphere sintering: The green blank is placed in an atmosphere sintering furnace, and sintering is carried out using gradient heating and atmosphere control. Temperature is controlled throughout the process to prevent the shell from melting and spreading. Specific process: Heating and debinding stage: slowly heat to 550~620℃ at 3~5℃ / min, hold for 1~2h to completely remove polyvinyl alcohol binder and prevent the green body from cracking due to excessive heating. Low-temperature densification stage: Continue to raise the temperature to 1050~1100℃ at 2~3℃ / min, hold for 2~3h, the glass phase additive forms a trace liquid phase, fills the intergranular gaps, achieves preliminary densification, and retains the core-shell interface structure; High-temperature crystallization stage: slowly raise the temperature to 1240~1280℃ at a rate of 1~2℃ / min, hold for 3~4h, and introduce a nitrogen-oxygen mixed atmosphere (oxygen volume fraction 5%~8%) to suppress oxygen vacancy generation, stabilize the core-shell crystal phase structure, and avoid excessive diffusion of shell elements. Temperature control and cooling stage: The temperature is rapidly reduced to 850-900℃ at a rate of 4-6℃ / min, and then cooled to room temperature with the furnace. The rapid cooling locks the stress at the core-shell interface, prevents ferroelectric domain relaxation, and further improves bias stability.

[0026] The beneficial effects of this invention are as follows: Through optimized in-situ hydrothermal process, high dispersion of nucleus phase and directional uniform growth of shell are achieved, with a core-shell coating uniformity of over 98%, no bare cores and no shell agglomeration; the shell and nucleus phase are chemically bonded and firmly combined, effectively suppressing forced flipping of ferroelectric domains under DC bias.

[0027] Rare-earth composite doping precisely controls the lattice constant, combined with a complete core-shell structure, and the synergistic effect of specific ratios of transition metal oxide dopants, composite glass phase additives, and sintering aids. This achieves a mass change rate of ≤±11% over a wide temperature range of -55℃ to 125℃, superior to the X7R standard of ≤±15%. The dielectric constant remains stable at 2400~2600, with a dielectric loss ≤0.012, no sudden temperature drift, and a capacitance decay rate (20V / μm) of less than 9% under DC bias, while the dielectric constant retention rate (20V / μm) under DC bias is higher than 90%, significantly improving performance stability. It combines high bias stability, wide temperature stability, and high reliability, fully meeting the stringent application requirements of high-end MLCCs in automotive electronics, industrial control, and 5G communications. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the preparation process of an X7R ceramic dielectric material with DC bias characteristics disclosed in an embodiment of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1: A method for preparing X7R ceramic dielectric material with DC bias characteristics, such as Figure 1 As shown, it includes: Preparation of nucleus phase powder: Barium carbonate (BaCO3) and titanium dioxide (TiO2) were dissolved in deionized water at a molar ratio of 1:1.005. Ammonia was added to adjust the pH to 10.5. The mixture was then transferred to a hydrothermal reactor and kept at 180℃ for 9 hours. After centrifugation, washing, and vacuum drying, high-purity BaTiO3 nucleus phase powder with a purity ≥99.9% and a particle size of 60nm was obtained.

[0032] Pre-activation treatment: Disperse the nucleus powder in an ethanol-water mixed solvent (volume ratio 1:1), add 0.1wt% ammonium polyacrylate as a dispersant, and sonicate for 30 min to form a highly dispersed suspension.

[0033] Gradient dropwise control: A mixed precursor solution of dysprosium nitrate, barium carbonate and tetrabutyl titanate was prepared according to the shell doping amount. A dual-feed system was used to dropwise the core phase suspension and the NaOH alkaline solution with pH=13 at a rate of 0.5 mL / min. The pH of the reaction system was maintained at 12 throughout the process, and the temperature was controlled at 40℃.

[0034] Hydrothermal crystallization: A two-stage heating process is adopted—first, the temperature is increased to 100℃ at 1℃ / min and held for 1h to promote the adsorption and spreading of the precursor on the nucleus surface; then, the temperature is increased to 150℃ at 2℃ / min and held for 5h.

[0035] The post-treatment enhancement process is as follows: After the reaction is completed, the powder is washed three times each with deionized water and anhydrous ethanol by centrifugation, and then washed once with dilute acetic acid by centrifugation. The powder is then vacuum dried to obtain core-shell structured barium titanate powder with a shell thickness of 7 nm. The powder is uniformly coated without damage or impurities.

[0036] Powder premixing and wet ball milling: Weigh the self-made core-shell structured barium titanate powder, rare earth composite dopant, transition metal oxide dopant, composite glass phase additive and sintering aid according to the formula ratio. The composition includes 96.0% barium titanate powder with a core-shell structure, 1.2% Ho2O3 and Dy2O3 composite dopant (mass ratio 1:0.8), 0.6% Nb2O5 and Ta2O5 composite dopant (mass ratio 1:0.6), 1.8% composite glass phase aid (borosilicate: zinc borosilicate glass = 1:0.7), and 0.4% SrCO3 and Al2O3 sintering aid.

[0037] Add deionized water and dispersant (ammonium polyacrylate, added at 0.5% of the total powder mass), place in a planetary ball mill, ball-to-material ratio 3:1, speed 350 r / min, and ball mill for 8 hours.

[0038] Segmented pre-calcination treatment: The ball-milled slurry is spray-dried and granulated (inlet air temperature 180℃, outlet air temperature 100℃) to obtain granulated powder with good flowability; then the granulated powder is placed in a muffle furnace for segmented pre-calcination: the first stage is held at 480℃ for 2 hours to slowly remove organic impurities and residual solvents, avoiding rapid heating that could cause the core-shell structure to crack; the second stage is held at 880℃ for 4 hours to complete the solid-phase reaction and preliminary crystallization.

[0039] Dry pressing: Add binder (polyvinyl alcohol, 1.0% wt%) to the pre-calcined powder, granulate twice, and then dry press. The pressing pressure is 80 MPa and the holding pressure is 60 s.

[0040] Segmented atmosphere sintering: Temperature rise and de-adhesion stage: slowly heat to 550℃ at 3℃ / min and hold for 2 hours; Low-temperature densification stage: Continue to increase the temperature to 1050℃ at a rate of 3℃ / min, and hold for 3 hours; High-temperature crystallization stage: slowly increase the temperature to 1260℃ at a rate of 2℃ / min, hold for 3 hours, and introduce a nitrogen-oxygen mixed atmosphere (oxygen volume fraction 6%). Temperature control and cooling stage: rapidly cool down to 850℃ at 6℃ / min, and then cool down to room temperature with the furnace.

[0041] Example 2: A method for preparing an X7R ceramic dielectric material with DC bias characteristics includes: Preparation of nucleus phase powder: Barium carbonate (BaCO3) and titanium dioxide (TiO2) were dissolved in deionized water at a molar ratio of 1:1.005. Ammonia was added to adjust the pH to 11. The mixture was then transferred to a hydrothermal reactor and kept at 190℃ for 8 hours. After centrifugation, washing, and vacuum drying, high-purity BaTiO3 nucleus phase powder with a purity ≥99.9% and a particle size of 80nm was obtained.

[0042] Pre-activation treatment: Disperse the nucleus powder in an ethanol-water mixed solvent (volume ratio 1:1), add 0.2wt% ammonium polyacrylate as a dispersant, and sonicate for 50 min to form a highly dispersed suspension.

[0043] Gradient dropwise control: A mixed precursor solution of dysprosium nitrate, barium carbonate and tetrabutyl titanate was prepared according to the shell doping amount. A dual-feed system was used to dropwise the core phase suspension and the NaOH alkaline solution with pH=13.5 at a rate of 0.4 mL / min. The pH of the reaction system was maintained at 13 throughout the process, and the temperature was controlled at 50℃.

[0044] Hydrothermal crystallization: A two-stage heating process is adopted—first, the temperature is increased to 120℃ at 3℃ / min and held for 2 hours to promote the adsorption and spreading of the precursor on the nucleus surface; then, the temperature is increased to 140℃ at 2℃ / min and held for 6 hours.

[0045] The post-treatment enhancement process is as follows: After the reaction is completed, the powder is washed three times each with deionized water and anhydrous ethanol by centrifugation, and then washed once with dilute acetic acid by centrifugation. The powder is then vacuum dried to obtain core-shell structured barium titanate powder with a shell thickness of 10 nm, uniform coating without damage or impurities.

[0046] Powder premixing and wet ball milling: Weigh the self-made core-shell structured barium titanate powder, rare earth composite dopant, transition metal oxide dopant, composite glass phase additive and sintering aid according to the formula ratio. The composition includes 97.5% barium titanate powder with a core-shell structure, 0.8% Ho2O3 and Dy2O3 composite dopant (mass ratio 1:0.8), 0.3% Nb2O5 and Ta2O5 composite dopant (mass ratio 1:0.6), 1.2% composite glass phase aid (borosilicate: zinc borosilicate glass = 1:0.7), and 0.2% SrCO3 and Al2O3 sintering aid.

[0047] Add deionized water and dispersant (ammonium polyacrylate, added at 0.5% of the total powder mass), place in a planetary ball mill, ball-to-material ratio 5:1, speed 400 r / min, and ball mill for 12 h.

[0048] Segmented pre-calcination treatment: The ball-milled slurry is spray-dried and granulated (inlet air temperature 200℃, outlet air temperature 90℃) to obtain granulated powder with good flowability; then the granulated powder is placed in a muffle furnace for segmented pre-calcination: the first stage is held at 450℃ for 3 hours to slowly remove organic impurities and residual solvents, avoiding rapid heating that could cause the core-shell structure to crack; the second stage is held at 850℃ for 4 hours to complete the solid-phase reaction and preliminary crystallization.

[0049] Dry pressing: Add binder (polyvinyl alcohol, 1.0% wt%) to the pre-fired powder, granulate twice, and then dry press. The pressing pressure is 120 MPa and the holding pressure is 30 s.

[0050] Segmented atmosphere sintering: Temperature rise and de-adhesion stage: slowly heat to 550℃ at 3℃ / min and hold for 2 hours; Low-temperature densification stage: Continue to increase the temperature to 1050℃ at a rate of 3℃ / min, and hold for 3 hours; High-temperature crystallization stage: slowly increase the temperature to 1260℃ at a rate of 2℃ / min, hold for 3 hours, and introduce a nitrogen-oxygen mixed atmosphere (oxygen volume fraction 6%). Temperature control and cooling stage: rapidly cool down to 900℃ at 6℃ / min, and then cool down to room temperature with the furnace.

[0051] Comparative Example 1: In the preparation of the core and shell, the pre-activation treatment was omitted (no sonication, no dispersant added, the core phase was directly dispersed in an ethanol-water mixed solvent), and the rest of the preparation process was the same as in Example 1.

[0052] Comparative Example 2: In the core-shell preparation, gradient drop addition control was eliminated. The mixed precursor solution and alkali solution were poured into the core phase suspension at one time, and the drop rate was not controlled. The rest of the preparation process was the same as in Example 1.

[0053] Comparative Example 3: In the core-shell preparation, the two-stage hydrothermal heating was eliminated, and a one-step heating process was adopted (heating to 150℃ at 2℃ / min and holding for 5h). The 100℃ holding adsorption was omitted. The remaining core-shell preparation processes (pre-activation, gradient addition, post-treatment), ceramic formulation, and preparation process were consistent with Example 1. Objective: To verify the effect of the two-stage heating on the bonding force between the shell and the core, and the crystallinity.

[0054] Comparative Example 4 The composition of the core-shell structured barium titanate powder was 96.0%, Ho2O3 and Dy2O3 composite dopant was 1.2% (mass ratio 1:0.3), Nb2O5 and Ta2O5 composite dopant was 0.6% (mass ratio 1:1), composite glass phase aid was 1.8% (borosilicate: zinc borosilicate glass = 1:1.3), and SrCO3 and Al2O3 sintering aid was 0.4%. The remaining preparation process was the same as in Example 1.

[0055] Comparative Example 5 The composition includes 94.0% barium titanate powder with a core-shell structure, 2.2% Ho2O3 and Dy2O3 composite dopant (mass ratio 1:0.8), 0.6% Nb2O5 and Ta2O5 composite dopant (mass ratio 1:0.6), 2.8% composite glass phase additive (borosilicate: zinc borosilicate glass = 1:0.7), and 0.4% SrCO3 and Al2O3 sintering aid.

[0056] Comparative Example 6 In the core-shell preparation, the shell thickness was controlled to 13nm (exceeding the 5~10nm optimization range) by adjusting the amount of precursor feed. The rest of the preparation process was the same as in Example 1.

[0057] Comparative Example 7 Segmented atmosphere sintering: directly heat to 1260℃ at a slow rate of 2℃ / min, hold for 3h, and introduce a nitrogen-oxygen mixed atmosphere (oxygen volume fraction 6%); temperature control and cooling stage: rapidly cool to 850℃ at a rate of 6℃ / min, and then cool to room temperature with the furnace. The rest of the preparation process is the same as in Example 1.

[0058] The performance data of Examples 1-2 and Comparative Examples 1-7 of the present invention are shown in Table 1.

[0059] Table 1: Performance data of Examples 1-2 and Comparative Examples 1-7

[0060] Examples 1-2 demonstrate excellent performance across all aspects, meeting the X7R standard and exhibiting outstanding DC bias stability, thus verifying the feasibility and rationality of the optimized core-shell fabrication process and overall technical solution. Comparative Example 1 (without pre-activation): Nuclear phase aggregation leads to uneven shell coating, and a decrease in dielectric constant and density, verifying the key role of pre-activation treatment in nuclear phase dispersion and shell uniformity; Comparative Example 2 (without gradient dropping): The dielectric loss increased significantly, verifying the necessity of gradient dropping to suppress homogeneous nucleation and ensure directional growth of the shell; Comparative Example 3 (without two-stage heating): The shell and core are loosely bonded, and the performance fluctuates greatly, verifying the importance of two-stage heating in improving the crystallinity and bonding strength of the shell; Comparative Examples 4-5 (with altered materials and formulation): Density decreased, and all indicators were significantly reduced, validating the rationality of the component ratio.

[0061] Comparative Example 6 (shell thickness exceeds the standard): The dielectric constant decreased significantly, and the overall performance was inferior to the example, verifying the rationality of the shell thickness optimization range of 5~10nm.

[0062] Comparative Example 7 (segmented atmosphere sintering changed to one-step sintering): the dielectric constant decreased significantly, and all indicators were significantly reduced. Gradient heating + atmosphere-controlled sintering proved that temperature control throughout the process can avoid shell melting and diffusion, and further improve bias stability.

[0063] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A DC bias characteristic X7R ceramic dielectric material, characterized in that, It consists of the following components by mass percentage: The core-shell structured barium titanate powder prepared by in-situ hydrothermal method contains 96.0%~97.5% rare earth composite dopant, 0.8%~1.5% transition metal oxide dopant, 0.3%~0.6% composite glass phase additive, 1.2%~2.0% composite glass phase additive, and 0.2%~0.5% sintering aid; the sum of the contents of the above components is 100%. The core-shell structured barium titanate powder has a core phase of high-purity BaTiO3 with a purity ≥99.9% and a particle size of 50~80nm, and a shell phase of Dy with a doping amount of 0.3%~0.8wt%. 3+ BaTiO3 doping, shell thickness 5~10nm, coating uniformity ≥98%; The rare earth composite dopant is a mixture of Ho2O3 and Dy2O3 in a mass ratio of 1:0.6 to 1:1.2; the transition metal oxide dopant is a mixture of Nb2O5 and Ta2O5 in a mass ratio of 1:0.4 to 1:0.8; the composite glass phase aid is a mixture of borosilicate glass and zinc borosilicate glass in a mass ratio of 1:0.5 to 1:1; and the sintering aid is a mixture of SrCO3 and Al2O3.

2. A method for preparing the X7R ceramic dielectric material with DC bias characteristics as described in claim 1, characterized in that, The process includes two stages: pre-preparation of core-shell barium titanate and ceramic sintering. The specific steps are as follows: (1) Preparation of core-shell structured barium titanate powder Core phase synthesis: Using barium carbonate and titanium dioxide as raw materials, high-purity BaTiO3 core phase powder with a purity ≥99.9% and a particle size of 50~80nm was obtained by hydrothermal method; Shell coating: Pre-activation treatment: Disperse the core phase powder in an ethanol-water mixed solvent, add 0.1~0.2wt% ammonium polyacrylate as a dispersant, and ultrasonically vibrate for 30~50min to form a highly dispersed suspension; Gradient dropwise control: Prepare a mixed precursor solution of dysprosium nitrate, barium carbonate and tetrabutyl titanate according to the shell doping amount. Use a dual-feed system to dropwise the core phase suspension and NaOH alkaline solution with pH=13~13.5 at a rate of 0.4~0.6 mL / min. Maintain the pH of the reaction system at 12~13 throughout the process and control the temperature at 40~50℃. Hydrothermal crystallization: The mixed slurry is transferred to a hydrothermal reactor, first heated to 100-120℃ at 1-3℃ / min and held for 1-2 hours; then heated to 140-160℃ at 2-5℃ / min and held for 4-6 hours to complete the crystallization process. 3+ In-situ growth of BaTiO3-doped shells; Post-processing enhancement: After the reaction was completed, the powder was washed by centrifugation with deionized water and anhydrous ethanol, then washed by centrifugation with dilute acetic acid, and vacuum dried to obtain core-shell structured barium titanate powder. (2) Preparation of ceramic dielectric materials Powder premixing and wet ball milling: Weigh each component according to the formula, add deionized water and ammonium polyacrylate dispersant, ball-to-material ratio 3:1~5:1, speed 300~400r / min, ball mill for 8~12h to obtain a uniform slurry; Segmented pre-calcination: After spray drying and granulation of the slurry, it is pre-calcined in segments at 450~500℃ for 2~3 hours and 850~900℃ for 3~4 hours to obtain pre-calcined powder; Dry pressing: Add polyvinyl alcohol binder to the pre-fired powder, dry press at 80~120MPa pressure, hold pressure for 30~60s to obtain green body; Segmented atmosphere sintering: The green body is held at 550~620℃ for debinding, held at 1050~1100℃ for densification, held at 1240~1280℃ for crystallization, and then rapidly cooled in the furnace to obtain the finished product.

3. The preparation method according to claim 2, characterized in that, In the nucleus phase synthesis step, barium carbonate and titanium dioxide are dissolved in deionized water at a molar ratio of 1:1.005, ammonia is added to adjust the pH to 10-11, the mixture is transferred to a hydrothermal reactor, kept at 180-200℃ for 8-10 hours, centrifuged, washed, and vacuum dried to obtain high-purity BaTiO3 nucleus phase powder with a purity ≥99.9% and a particle size of 50-80nm.

4. The preparation method according to claim 2, characterized in that, The post-treatment enhancement process involves washing the product three times each with deionized water and anhydrous ethanol, followed by washing it once with dilute acetic acid. The product is then vacuum dried to obtain core-shell structured barium titanate powder with a shell thickness of 5-10 nm.

5. The preparation method according to claim 2, characterized in that, The inlet air temperature for the segmented pre-calcination spray drying granulation is 180~200℃, and the outlet air temperature is 90~100℃.

6. The preparation method according to claim 2, characterized in that, The segmented atmosphere sintering includes: slowly heating to 550-620℃ at a rate of 3-5℃ / min, holding at that temperature for 1-2 hours, and completely removing the polyvinyl alcohol binder. Low-temperature densification stage: Continue to raise the temperature to 1050~1100℃ at a rate of 2~3℃ / min, and hold for 2~3 hours to achieve initial densification; High-temperature crystallization stage: slowly raise the temperature to 1240~1280℃ at a rate of 1~2℃ / min, hold for 3~4 hours, and introduce a nitrogen-oxygen mixed atmosphere with an oxygen volume fraction of 5%~8%. Temperature control and cooling stage: rapidly cool down to 850~900℃ at a rate of 4~6℃ / min, and then cool down to room temperature with the furnace.

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