Boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC and preparation method of boron-nitrogen co-doped barium titanate ceramic

Abstract

The invention relates to the technical field of electronic ceramic media, in particular to boron-nitrogen co-doped barium titanate ceramic for an X5R type MLCC and a preparation method of the boron-nitrogen co-doped barium titanate ceramic. The invention discloses a boron-nitrogen co-doped barium titanate ceramic for an X5R type MLCC and a preparation method of the boron-nitrogen co-doped barium titanate ceramic, and the preparation method comprises the following steps: synthesizing calcium and zirconium co-doped barium titanate nanocrystalline powder through hydrothermal coprecipitation; and uniformly coating the surface of the powder with a reaction precursor containing boron, nitrogen and fluorine elements by adopting a liquid-phase mechanochemical method, and carrying out spray drying to obtain the composite powder. The composite powder is mixed with self-made low-temperature glass powder and an organic carrier to prepare tape casting slurry, and a green body is prepared through tape casting, printing of a nickel inner electrode, lamination and isostatic pressing. According to the method, no rare earth element is added, low-temperature co-firing with a nickel electrode is achieved, the capacitance change rate of the prepared ceramic dielectric within the temperature range of-55-85 DEG C is smaller than or equal to + / -10%, the insulation resistance at 125 DEG C is larger than or equal to 6.21 * 10 < 11 > ohm, the ceramic dielectric has the high dielectric constant, low loss and high reliability, and a new material system is provided for rare-earth-free high-performance MLCC.

Description

Technical Field

[0001] This invention relates to the field of electronic ceramic dielectric technology, specifically to a boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs and its preparation method. Background Technology

[0002] Barium titanate-based dielectric ceramics are widely used as dielectric materials for multilayer ceramic capacitors (MLCCs) due to their high dielectric constant and excellent ferroelectric properties. The specifications X7R, X8R, and X5R refer to dielectric temperature stability requirements. For example, X7R requires capacitance variation of no more than ±15% within the range of -55℃ to 125℃, X8R extends to ±15% within 150℃, and X5R requires ±15% within the range of -55℃ to 85℃. In recent years, automotive-grade and high-reliability applications require dielectrics to maintain small capacitance variations over a wider temperature range, while also possessing high dielectric constants and low losses. However, achieving these properties typically requires multi-component doping modification of the barium titanate (BaTiO3) matrix and controlled sintering processes to obtain specific microstructures.

[0003] For example, CN120965309A discloses a method for preparing a defect-controlled barium titanate composite material. The preparation method includes the following steps: First, an appropriate amount of barium carbonate, titanium dioxide, nickel oxide, and dopant mixed powder are added to a ball mill jar for ball milling to obtain initial barium titanate composite particles. These particles are then dispersed in an aqueous solution of a growth inhibitor to react and form modified barium titanate composite powder. Subsequently, the obtained barium titanate composite powder is mixed with a binder, polyvinyl butyral, and pressed into a green blank. This blank is then cold isostatically pressed, sintered, annealed under a nitrogen atmosphere, and held at a certain temperature to obtain the defect-controlled barium titanate composite material. CN120717784A discloses a giant dielectric barium titanate-based ceramic dielectric material, its preparation method, and its application. The giant dielectric-based ceramic dielectric material includes barium titanate and doping elements, which are composed of Mg, Ca, RE, Al, and Si. The barium titanate content is 90~99.7 mol by molar percentage. The Mg content is 0.1~4 mol%, Ca content is 0.25~0.55 mol%, RE content is 0.1~3.5 mol%, Al content is 0.002~0.3 mol%, and Si content is 0.01~4.0 mol%. The ceramic dielectric material it provides has a small average grain size, a room temperature dielectric constant greater than 10⁴, exhibiting a giant dielectric constant, good dielectric stability over a wide temperature range, and a resistivity greater than 10⁹ Ω·cm. It employs a traditional solid-state process, making it suitable for large-scale industrialization. However, traditional techniques primarily rely on rare earth element doping to increase the Curie temperature and broaden the dielectric peak. Rare earth elements are expensive, their supply is limited, and they require high-temperature sintering above 1200℃, making co-firing with low-melting-point nickel internal electrodes impossible.

[0004] In summary, how to develop a novel barium titanate-based ceramic system that can achieve low-temperature sintering and co-firing with nickel electrodes, while ensuring high dielectric properties, wide temperature stability, and high reliability, and avoiding the use of expensive rare earth elements to reduce costs, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs and its preparation method, so as to solve the technical problems such as uneven doping and the contradiction between low temperature and high reliability in the prior art.

[0006] The specific technical solution is as follows: A boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC and its preparation method are disclosed. The preparation method involves preparing a composite precursor powder containing calcium, zirconium, boron, nitrogen and fluorine elements through hydrothermal co-precipitation and liquid phase coating processes. After tape casting and low-temperature co-firing with a nickel internal electrode, the precursor is triggered to react in situ at the grain boundaries during a specific cooling-holding stage to generate a composite insulating phase interwoven with hexagonal boron nitride and barium fluoride.

[0007] Furthermore, the hydrothermal coprecipitation involves simultaneously hydrolyzing and co-crystallizing barium, calcium, titanium, and zirconium sources in a nitrogen-protected alkaline hydrothermal environment to synthesize calcium and zirconium co-doped barium titanate nanoparticles with a perovskite (ABO3) structure in one step. During this process, calcium and zirconium ions enter the vertices (A-sites) and body center (B-sites) of the barium titanate lattice cube, respectively, during the initial nucleation stage, forming a chemically homogeneous pre-strained lattice framework. This lays the structural foundation for subsequent low-temperature sintering and performance control.

[0008] Furthermore, the liquid phase coating process involves placing the calcium and zirconium co-doped barium titanate nanoparticles in an alcoholic solution containing triethyl borate, urea, and barium fluoride. Through the mechanochemical action generated by high-energy sand milling, the active components containing boron, nitrogen, and fluorine are uniformly bonded to the powder surface at the molecular level, forming an amorphous coating layer. Subsequently, the precursor composite powder with good flowability is obtained by spray drying.

[0009] Furthermore, the aforementioned low-temperature co-firing involves simultaneously sintering and densifying the cast green body and the nickel internal electrode at a temperature of 900-950°C in a reducing atmosphere using self-made zinc borosilicate glass powder as a low-temperature sintering aid. This temperature window is significantly lower than the sintering temperature of traditional rare-earth doped systems and also lower than the oxidation critical point of nickel, thus achieving good compatibility with low-cost nickel while ensuring complete densification of the ceramic body.

[0010] Furthermore, the in-situ reaction is carried out after the ceramic has been densified and sintered, by precisely controlling the cooling process within a temperature range of 800~900℃, so that the boron, nitrogen and fluorine components in the coating layer diffuse and enrich at the grain boundaries and undergo solid-phase chemical reactions, thereby directionally generating a continuous insulating interface phase composed of two-dimensional hexagonal boron nitride nanosheets and barium fluoride matrix.

[0011] Furthermore, the composite insulating phase is a continuous interface structure existing between barium titanate grains. This structure is formed by interweaving two-dimensional hexagonal boron nitride nanosheets as an insulating framework with barium fluoride as an oxygen vacancy scavenger, and its thickness is 2-3 nm.

[0012] A boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs and its preparation method thereof, comprising the following steps: S1: Deionized water, ethanol, Ba(OH)2·8H2O and Ca(OH)2 were added to the alloy hydrothermal reactor, heated to 80℃ and stirred for 30 minutes; then Ti(OC4H9)4 and Zr(OC4H9)4 were added dropwise at 0.5 parts / min. After the addition was completed, the reactor lid was sealed, nitrogen was purged to replace the air, and the temperature was raised and kept at 12 hours; after the reaction was completed, the mixture was filtered and the filter cake was dried for 8 hours to obtain Ca / Zr co-doped BaTiO3 nanopowder.

[0013] S2: The obtained Ca / Zr co-doped BaTiO3 nanopowder was fed into a sand mill, and anhydrous ethanol, triethyl borate, urea, BaF2 and 0.3mm zirconia beads were added as grinding media. The mixture was circulated and ground for 2 hours. Then the slurry was transferred into a centrifugal spray drying tower, the inlet and outlet air temperatures were set, and the powder was collected after instant drying to obtain BNF uniformly coated precursor powder.

[0014] S3: Add a mixture of quartz sand, H3BO3, and ZnO to the planetary ball mill jar; after drying, sieve the mixture, pour it into a crucible and melt for 30 minutes, then quench it in water to form glass slag. The slag is then crushed, coarsely crushed, and finally pulverized using an air jet mill to D. 50 =0.8µm, to obtain self-made ZnO-B2O3-SiO2 glass powder. The obtained precursor powder, self-made ZnO-B2O3-SiO2 glass powder, PVB-79 binder, DBP plasticizer and a mixed solvent of anhydrous ethanol and toluene in a 1:1 mass ratio were added to a centrifugal degassing machine and subjected to planetary ball milling; after vacuum degassing for 30 minutes, a casting slurry was obtained.

[0015] S4: The casting paste is used to prepare a green strip with a thickness of 3.0±0.2µm on a casting machine. After the green strip is dried with hot air, it is wound up and transferred to a clean room. Electrode patterns are printed using a printing machine with 250-mesh nickel electrode paste. The printed strip is then stacked 10 layers on a small laminating machine with lamination parameters of 80℃, 20MPa, and 10 minutes. After isostatic pressing, it is diced into 0402 green chips using a dicing machine. The green chips are first debonded in a tube furnace, then heated to achieve dense sintering, followed by uniform cooling and constant temperature. After that, the power is turned off and the furnace is cooled to room temperature. The ceramic wafers are deburred using a roller chamfering machine, then impregnated with end sealant, and electroplated with nickel-tin at 800℃ to obtain the boron-nitrogen co-doped barium titanate ceramic product for X5R type MLCCs.

[0016] Further, the Ca(OH)2 in S1 has a mass composition of 0.40~0.60 parts; the Zr(OC4H9)4 has a mass composition of 0.60~0.80 parts; and the heating and holding for 12 hours requires heating to 150~170℃.

[0017] Further, in S2, the triethyl borate, urea, and BaF2 have mass components of 0.40~0.60 parts, 0.20~0.40 parts, and 0.10~0.30 parts, respectively; the set inlet and outlet air temperatures are wherein the inlet air temperature is set to 170~190℃.

[0018] Furthermore, the self-made ZnO-B2O3-SiO2 glass powder mentioned in S3 is added at a mass ratio of 0.3~0.8 parts; the PVB-79 binder, DBP plasticizer, and the mixed solvent of anhydrous ethanol and toluene in a mass ratio of 1:1 are composed of 0.5~0.7 parts, 0.2~0.4 parts, and 5~7 parts, respectively; the planetary ball mill is set to a rotational linear velocity of 1~3 m / s and a revolution linear velocity of 4~6 m / s for 2~4 hours.

[0019] Furthermore, the heating and densification sintering described in S4 requires heating to 900~950℃; the uniform cooling and constant temperature setting is to cool to 800~900℃ at a rate of 1~3℃ / min and hold the temperature for 2~10 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) Uniform doping and reasonable structure: B, N and F doping is introduced by using precursor solution coating and spray drying to avoid the uneven doping caused by simple mixing. Ca and Zr are pre-solidified during the synthesis of nanoscale powder, which greatly reduces element segregation during sintering. The sintered ceramics exhibit a uniform and dispersed microstructure with uniform grain size distribution. Thin layers of h-BN and BaF2 phases continuously cover the grain boundaries, realizing a uniform nanoscale core-shell structure instead of the traditional large-size core-shell domain structure, ensuring the consistency of performance of ceramics from different batches and different rows.

[0021] (2) Low-temperature sintering and high dielectric properties: The co-firing temperature is reduced to about 920℃ by using ZnO-B2O3-SiO2 glass phase sintering, which can be matched with nickel electrodes for co-firing. Although a glass phase is added, the dielectric constant is still high thanks to the adjustment of the lattice and appropriate grain size by Ca and Zr.

[0022] (3) Wide temperature stability: The synergistic effect of the dispersion phase transition caused by N and F co-doping and the grain boundary stress effect of h-BN significantly broadens the dielectric constant-temperature response peak of the material, and the dielectric stability of the material is greatly enhanced at high temperature.

[0023] (4) High insulation reliability: The grain boundary h-BN and BaF2 layers effectively block the migration of oxygen vacancies between grains, while fluorine ion compensation doping reduces the oxygen vacancy concentration in the lattice, significantly reducing leakage channels and enabling the ceramic to exhibit excellent insulation resistance under high temperature and high pressure. At the same time, the isovalent doping of Ca and Zr avoids the introduction of excessive mobile charges, and boron nitride itself is heat-resistant and non-conductive, comprehensively ensuring the stability and lifespan of the material under high temperature and high pressure. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating a boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs and its preparation method, according to the present invention.

[0025] Figure 2 This is a schematic diagram of the perovskite-type barium titanate crystal structure in Example 1 of the present invention.

[0026] Figure 3 The image shows the X-ray diffraction pattern of the ceramic obtained in Example 1 of this invention.

[0027] Figure 4 This is an HRTEM image of the ceramic grain boundaries in Embodiment 1 of the present invention.

[0028] Figure 5 This is a comparison chart of the experimental results of dielectric constant, dielectric loss, insulation resistance, and capacitance change rate in Experiment Example 1 of the present invention.

[0029] Figure 6 This is a comparison chart of the experimental results of the volumetric temperature characteristics of Example 1 of the present invention and Comparative Examples 1 and 2. Detailed Implementation

[0030] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0031] The technical solution designed by this invention to solve the existing problems includes the following key points: 1. Molecular-level precursor synthesis process Traditional processes rely on mechanical ball milling to mix commercially available barium titanate powder with dopant oxides, resulting in uneven elemental distribution and low sintering activity, necessitating diffusion driven by temperatures above 1300℃. This approach differs from traditional physical mixing methods, employing a chemical assembly path of hydrothermal co-precipitation followed by in-situ liquid-phase coating. The core principle is as follows: First, in a hydrothermal reactor, a pre-prepared titanium / zirconium composite hydroxide sol is uniformly mixed with barium and calcium salt solutions. During the mixing process, the Ba in the solution... 2+ and Ca 2+ The ions are then adsorbed onto the sol surface; under hydrothermal conditions at 160°C, these ions undergo dehydration condensation following the spatial template of the perovskite-type crystal structure (ABO3), such as... Figure 2 As shown, in this structure, Ba 2+ With smaller radius Ca 2+ Competition for large cation sites (A sites) located at the vertices of the lattice, Ti 4+ With larger radius Zr 4+ Competition occupies small cation sites (B sites) located at the lattice center, while O 2- These are located at the six face centers of the cubic lattice, a mechanism that ensures that dopant ions are embedded into the lattice in the initial stages of crystal growth. For example... Figure 3 As shown, all diffraction peaks can be precisely indexed to a pure perovskite structure, and no characteristic peaks of a second phase are observed. The (200) diffraction peak has a symmetrical and uniform shape without splitting, directly confirming that the material possesses a highly symmetrical cubic crystal structure at room temperature. This XRD result indicates that through a hydrothermal co-precipitation process, Ba... 2+ With Ti 4+ It has been successfully dissolved into the barium titanate lattice. The (Ba,Ca)(Ti,Zr)O3 crystal nuclei formed in this process, due to Ca 2+ A-site contraction and Zr 4+ The resulting B-site expansion produces symmetrical lattice strain, constructing a stable framework with intrinsic stress.

[0032] By utilizing mechanochemical energy in a sand mill, triethyl borate, urea, and BaF2 undergo molecular-level adsorption and partial chemical reactions on the powder surface, forming a uniform active shell. This process is not essentially physical mixing between particles, but rather a solid-liquid interface reaction based on mechanochemical activation. Driven by high-frequency shearing and collision mechanical energy, the powder surface lattice undergoes instantaneous distortion and bond breaking, forming highly active sites, primarily surface Ti-OH and coordinatingly unsaturated Ti. 4+ Simultaneously, triethyl borate undergoes partial alcoholysis and hydrolysis under the combined action of mechanical force and trace amounts of water, generating oligoboroxane intermediates containing BOB bonds. These active boron species rapidly condense with Ti-OH on the powder surface through their terminal -OH or -OC2H5 groups to form Ti-OB covalent bonds. Meanwhile, urea decomposes to provide NH3 / NH2. + The nitrogen element reacts with the B-OH groups on the surface of the boron species anchored above, introducing nitrogen into the surface layer; BaF2 nanoparticles are then anchored to the negatively charged surface through chemisorption. Therefore, B, N, and F elements are not mechanically attached as independent phases, but rather fixed to the powder surface in monolayers or a few atomic layers by forming chemical bonds with hydroxyl groups or metal sites on the powder surface. Thus, the final product is not a mixture, but a highly reactive precursor with a "core-shell structure," namely, a uniform (Ba,Ca)(Ti,Zr)O3 core and a molecular-level active layer of B, N, Ba, and F anchored to its surface by chemical bonds as a shell, with each component in molecular-level contact and a metastable state.

[0033] 2. Low-temperature kinetic matching sintering process Traditional X5R materials rely on long-range diffusion of rare earth ions at high temperatures to form a "core-shell structure" to achieve their performance, leading to a severe contradiction between the sintering temperature and the applicable temperature of inexpensive nickel electrodes. This invention transforms the densification mechanism from solid-phase diffusion to liquid-phase viscous flow through a ZnO-B2O3-SiO2 low-temperature glass phase and precise atmosphere-temperature window control. The self-made ZnO-B2O3-SiO2 low-temperature glass phase has a mass ratio of B2O3:ZnO:SiO2 of 47:31:22. The composition of this glass phase is designed based on the structure and performance relationship of the borosilicate glass system. A high content of B2O3 ensures a low softening point; an appropriate amount of SiO2 provides the necessary high-temperature viscosity and stability; and the key component ZnO, as a network intermediate, can form ZnO4 structural units at temperatures above 900℃, significantly improving the polymerization degree of the glass network at high temperatures, thus resulting in a plateau region in its viscosity-temperature curve around 920℃. Therefore, through precise composition design, the softening point of this glass phase was lowered to 880°C, and it provides 10 at 920°C. 4 ~10 5The optimal viscosity at Pa·s. This glassy phase not only acts as a sintering aid, but its Zn... 2+ Furthermore, it bonds with the BaTiO3 interface, achieving densification of the liquid phase through viscous flow while actively pinning grain boundaries and stabilizing the microstructure.

[0034] Based on the aforementioned material system, this invention precisely matches the sintering temperature within the optimal window defined by the effective flow initiation temperature of the glass phase and the critical oxidation temperature of the nickel electrode. The principle is as follows: in a N2-5%H2 reducing atmosphere, the temperature is precisely controlled within a narrow process equilibrium window of 900-950℃. This window is based on three limiting conditions: its lower limit is determined by the effective liquid phase sintering initiation temperature of the ZnO-B2O3-SiO2 glass phase used; below this temperature, the liquid phase viscosity is too high, making densification impossible. Its upper limit is strictly limited by the critical oxidation temperature of the nickel internal electrode in the reducing atmosphere; above this temperature, electrode failure will occur. Simultaneously, this temperature window falls precisely within the optimal kinetic range where the organic components in the precursor have been completely thermally desorbed, while the ceramic grains have not yet entered the optimal kinetic range for rapid abnormal growth. Therefore, precisely controlling this temperature is a feasible path to achieve complete densification of the ceramic body through low-temperature liquid phase viscous flow, while ensuring the integrity of the electrode, utilizing the standard industrial capabilities of an atmosphere sintering furnace. This provides an ideal, defect-free, fine-grained matrix for subsequent in-situ grain boundary reactions to construct nanocomposite structures.

[0035] 3. In-situ grain boundary engineering process In traditional ceramics, grain boundaries are passive byproducts of random segregation of impurity elements during sintering, resulting in uneven composition and thickness, and are a weak point in performance. This invention, after densification, designs a non-equilibrium cooling-isothermal heat treatment mechanism, which is a diffusion-controlled multiphase interface reaction process. It utilizes the chemical potential gradient of pre-coated B, N, and F components at the grain boundaries in the precursor, driving their selective grain boundary segregation. Within a specific thermodynamic window of 850℃, these grain boundary-rich active species trigger a heterogeneous reaction with a dissolution and exudation mechanism.

[0036] First, amorphous B₂O₃ and nitrogen-containing decomposition products adsorb and partially eutectic on the surface of BaF₂ grains, forming a liquid-phase thin layer with a BON structure. Subsequently, thanks to the similarity in crystal structure and specific orientation relationship between the (111) crystal plane of BaF₂ and the (002) crystal plane of h-BN, the B and N atoms in this thin layer can rearrange in an orderly manner under the guidance of the crystal template, thus significantly reducing the nucleation energy barrier of h-BN. Finally, B and N atoms diffuse through the interface and grow epitaxially on the template, stacking layer by layer to form hexagonal boron nitride nanosheets with a typical layered structure. Throughout the process, BaF₂ not only serves as a fluorine source but also acts as a catalytic substrate for heterogeneous nucleation and a crystal growth template, ensuring the directional and uniform synthesis of h-BN nanosheets at the grain boundaries. Driven by the minimization of interfacial energy, this process ultimately self-assembles into a layered composite structure, actively constructing a continuous and uniform h-BN nanosheet-BaF₂ composite insulating grain boundary with a thickness of only 2-3 nanometers. To confirm this structure at the atomic scale, high-resolution transmission electron microscopy (HRTEM) analysis was performed in this invention. Figure 4 As shown in the figure, the region displaying continuous layered stripes corresponds to the hexagonal boron nitride phase, while the clusters of discrete stripes with different orientations and spacings correspond to barium fluoride nanoparticles. The lattice stripes of the two phases are directly connected at the interface, without any amorphous layer for separation. This observation is corroborated by the XRD phase analysis results, jointly confirming the formation of the h-BN / BaF2 composite grain boundary structure. This structure hinders carrier migration through its nanoscale physical barrier, broadens the dielectric temperature spectrum using localized stress generated by lattice distortion, and achieves defect stabilization through the specific binding of fluoride ions and oxygen vacancies. Ultimately, a high-performance insulating interface is created at the mesoscale, which is not found in traditional materials.

[0037] Example 1 Table 1 Raw Material Information Table A boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs and its preparation method thereof, comprising the following steps: S1: 45 parts deionized water, 15 parts ethanol, 24.8 parts Ba(OH)2·8H2O and 0.45 parts Ca(OH)2 were added to an alloy hydrothermal reactor, heated to 80℃ and stirred at 300 rpm for 30 minutes with an anchor stirrer; then 21.3 parts Ti(OC4H9)4 and 0.65 parts Zr(OC4H9)4 were added dropwise at 0.5 parts / min using a peristaltic pump. After the addition was completed, the reactor lid was sealed, nitrogen was purged to replace the air, and the temperature was raised to 160℃ and held for 12 hours; after the reaction was completed, the mixture was filtered through a Buchner funnel, and the filter cake was dried in an 80℃ forced-air drying oven for 8 hours to obtain 10 parts Ca / Zr co-doped BaTiO3 nanopowder.

[0038] S2: Ten parts of the obtained nanoparticle powder were added to a sand mill, along with 20 parts of anhydrous ethanol, 0.48 parts of triethyl borate, 0.28 parts of urea, 0.12 parts of BaF2, and 0.3 mm zirconia beads as grinding media. The mixture was circulated and ground at 2000 rpm for 2 hours. Subsequently, the slurry was transferred to a centrifugal spray drying tower, with the inlet air temperature set to 180°C, the outlet air temperature to 85°C, and the rotary table speed to 24000 rpm. After instantaneous drying, the powder was collected to obtain 10.2 parts of BNF-coated precursor powder with a loose packing density of 0.42 g / cm³. 3 .

[0039] S3: Add 22 parts quartz sand, 47 parts H3BO3, and 31 parts ZnO to a planetary ball mill jar, mix at 300 rpm for 2 hours; after drying, pass through a 200-mesh sieve, pour into an alumina crucible, melt at 1000℃ for 30 minutes, water quench to form glass slag, crush the slag with a jaw crusher, coarsely crush it with an agate mortar, and then grind it to D using an air jet mill. 50 =0.8µm, to obtain self-made ZnO-B2O3-SiO2 glass powder. 10.2 parts of the obtained precursor powder, 0.5 parts of the self-made ZnO-B2O3-SiO2 glass powder, 0.6 parts of PVB-79 binder, 0.3 parts of DBP plasticizer, and 6 parts of a 1:1 mixture of anhydrous ethanol and toluene were added to a centrifugal degassing machine. The mixture was then ball-milled for 3 hours at a planetary speed of 2 m / s rotation and 5 m / s revolution. After vacuum degassing for 30 minutes, a casting slurry with a solid content of 54 wt% and a viscosity of 3.2 Pa·s was obtained.

[0040] S4: The casting paste is used to prepare a green strip with a thickness of 3.0±0.2µm on a casting machine. After drying the green strip with hot air at 90℃, it is wound up and transferred to a clean room. Electrode patterns are printed using a printing machine with 250-mesh nickel electrode paste. The printed strip is then laminated 10 times on a small laminator with lamination parameters of 80℃, 20MPa, and 10 minutes. After isostatic pressing, it is diced into 0402 green chips using a dicing machine. The green chips are first debonded at 350℃ in a tube furnace, then heated to 920℃ for dense sintering. Subsequently, the temperature is lowered to 850℃ at 2℃ / min and held at that temperature for 6 hours. This allows the B2O3-urea-BaF2 to form an h-BN nanosheet-BaF2 composite phase in situ at the grain boundaries. At the same time, F- passivates oxygen vacancies, forming 2~3nm insulating grain boundaries. This results in a capacitance change of ≤±10% within -55~150℃ and an insulation resistance of ≥8×10 at 125℃. 11Ω. The microstructure of the ceramic samples was characterized using HRTEM. First, electron-transparent thin films were prepared in specific regions of the ceramic cross-section using focused ion beam technology. Subsequently, the overall morphology and elemental distribution contrast of the grain boundaries were observed under field emission transmission electron microscopy using a high-angle annular dark-field imaging mode. Then, HRTEM was used to obtain atomic lattice fringes of the grain boundary region to resolve its crystal structure. HRTEM revealed that the interface phase was composed of interwoven h-BN nanosheets and BaF2. The ceramic wafers were deburred using a tumbler chamfering machine, then impregnated with end-capping slurry and electroplated with nickel-tin at 800℃ to obtain the boron-nitrogen co-doped barium titanate ceramic product for X5R type MLCCs.

[0041] Example 2 The preparation method is the same as in Example 1, except that: S1: 0.45 parts Ca(OH)2 are replaced with 0.40 parts Ca(OH)2; 0.65 parts Zr(OC4H9)4 are replaced with 0.60 parts Zr(OC4H9)4; heating to 160℃ is replaced with heating to 150℃; S2: Replace 0.48 parts triethyl borate, 0.28 parts urea, and 0.12 parts BaF2 with 0.40 parts triethyl borate, 0.20 parts urea, and 0.10 parts BaF2; replace the set air inlet temperature of 180°C with the set air inlet temperature of 170°C; S3: Replace 0.5 parts of self-made ZnO-B2O3-SiO2 glass powder with 0.3 parts of self-made ZnO-B2O3-SiO2 glass powder; replace 0.6 parts of PVB-79 binder, 0.3 parts of DBP plasticizer and 6 parts of anhydrous ethanol and toluene in a 1:1 mass ratio with 0.5 parts of PVB-79 binder, 0.2 parts of DBP plasticizer and 5 parts of anhydrous ethanol and toluene in a 1:1 mass ratio with 5 parts of anhydrous ethanol and toluene in a 1:1 mass ratio with 5 parts of DBP plasticizer; replace 3 hours of planetary ball milling with a rotational linear velocity of 2 m / s and a revolution linear velocity of 5 m / s with 2 hours of planetary ball milling with a rotational linear velocity of 1.5 m / s and a revolution linear velocity of 4 m / s. S4: The process of heating to 920℃ for dense sintering is replaced with heating to 900℃ for dense sintering; the process of cooling to 850℃ at 2℃ / min and holding at that temperature for 6 hours is replaced with cooling to 800℃ at 1℃ / min and holding at that temperature for 2 hours. All other steps are the same.

[0042] Example 3 The preparation method is the same as in Example 1, except that: S1: 0.45 parts Ca(OH)2 are replaced with 0.60 parts Ca(OH)2; 0.65 parts Zr(OC4H9)4 are replaced with 0.80 parts Zr(OC4H9)4; heating to 160℃ is replaced with heating to 170℃; S2: Replace 0.48 parts triethyl borate, 0.28 parts urea, and 0.12 parts BaF2 with 0.80 parts triethyl borate, 0.40 parts urea, and 0.30 parts BaF2; replace the set air inlet temperature of 180°C with the set air inlet temperature of 190°C; S3: 0.5 parts of self-made ZnO-B2O3-SiO2 glass powder were replaced with 0.8 parts of self-made ZnO-B2O3-SiO2 glass powder; 0.6 parts of PVB-79 binder, 0.3 parts of DBP plasticizer and 6 parts of anhydrous ethanol and toluene in a 1:1 mass ratio were replaced with 0.8 parts of PVB-79 binder, 0.5 parts of DBP plasticizer and 7 parts of anhydrous ethanol and toluene in a 1:1 mass ratio; planetary ball milling at a rotational linear velocity of 2 m / s and a revolution linear velocity of 5 m / s for 3 hours was replaced with planetary ball milling at a rotational linear velocity of 3 m / s and a revolution linear velocity of 6 m / s for 4 hours; S4: The process of heating to 920℃ for dense sintering is replaced with heating to 950℃ for dense sintering; the process of cooling to 850℃ at 2℃ / min and holding at that temperature for 6 hours is replaced with cooling to 900℃ at 5℃ / min and holding at that temperature for 10 hours. All other steps are the same.

[0043] Comparative Example 1 The preparation method is the same as in Example 1, except that: S1: The steps of adding 0.45 parts Ca(OH)2 and 0.65 parts Zr(OC4H9)4 are omitted, and there is no co-doping of Ca and Zr; All other steps are the same.

[0044] Comparative Example 2 S2: The steps of adding 0.48 parts triethyl borate, 0.28 parts urea, and 0.12 parts BaF2 are omitted; All other steps are the same.

[0045] Comparative Example 3 The preparation method is the same as in Example 1, except that: S2: Omit the step of adding 0.12 parts of BaF2; All other steps are the same.

[0046] Comparative Example 4 The preparation method is the same as in Example 1, except that: S3: The steps of preparing and adding the self-made ZnO-B2O3-SiO2 glass powder are omitted; All other steps are the same.

[0047] Comparative Example 5 The preparation method is the same as in Example 1, except that: S4: The process of heating to 920℃ for dense sintering and then cooling down to 850℃ at 2℃ / min and holding the temperature for 6 hours is replaced with heating to 920℃ for dense sintering and then cooling down to room temperature at 2℃ / min, omitting the step of heating to 850℃ and holding the temperature for 6 hours. All other steps are the same.

[0048] Experimental Example 1 The barium titanate ceramic products prepared in Examples 1-3 and Comparative Examples 1-5 were measured: (1) Dielectric constant εr: Referring to GB / T 2693 "Fixed Capacitors for Electronic Equipment - Part 1: General Specification", barium titanate ceramic products were made into circular pieces with a diameter of 10 mm and a thickness of 0.5 mm, and both sides were coated with silver electrodes. The capacitance value was tested using a precision impedance analyzer at a frequency of 1 kHz, a test voltage of 1.0 Vrms, and a temperature of 25 °C. The room temperature dielectric constant was calculated based on the measured capacitance, sample thickness, and electrode area. Three samples of the finished product were used for the experiment, and the average value of the results was taken.

[0049] (2) Dielectric loss tanδ: Referring to GB / T 2693 "Fixed Capacitors for Electronic Equipment—Part 1: General Specification", barium titanate ceramic products were made into circular pieces with a diameter of 10 mm and a thickness of 0.5 mm, with silver electrodes on both sides. A precision impedance analyzer was used, with test conditions of frequency 1 kHz, test voltage 1.0 Vrms, and temperature 25 °C. Before the test, the system was calibrated at all ports using open circuit, short circuit, and a low-loss standard air capacitor. The residual loss of the system was recorded. In a shielded environment, the test voltage was set to 0.5 Vrms, and a parallel equivalent circuit mode was used to scan the frequency from 100 Hz to 1 MHz. The dielectric loss value of the final sample has been reduced by the residual loss of the system. Three finished products were tested, and the average value of the results was taken.

[0050] (3) Capacitive-Temperature Characteristics: Referring to GB / T 2693 "Fixed Capacitors for Electronic Equipment—Part 1: General Specification", barium titanate ceramic products were made into circular pieces with a diameter of 10 mm and a thickness of 0.5 mm, with silver electrodes on both sides. They were placed in a programmable high and low temperature test chamber and measured using a precision impedance analyzer and high and low temperature coaxial test leads at 1 kHz, 1.0 Vrms, and a temperature range of -55 to 150 °C. The temperature was varied at a rate of 0.5 °C / min, and measurements were taken after stabilizing at each characteristic temperature point for 30 minutes. The capacitance value C at 25 °C was used. 25 Using this as a baseline, calculate the rate of change of capacitance ΔC / C at each point. 25 Three batches of finished products were tested, and the average value of the results was taken.

[0051] (4) Insulation resistance: Referring to GB / T 2693 "Fixed capacitors for electronic equipment—Part 1: General specifications", the barium titanate ceramic product was made into a disc with a diameter of 10 mm and a thickness of 0.5 mm, with silver electrodes on both sides. The ceramic disc was tested using a high resistance meter and a three-terminal shielded fixture. After the sample was pretreated in a 125℃ oven for 24 hours, a 100V DC test voltage was applied at 125℃, and the stable value was read after charging for 60 seconds. Three samples of the finished product were tested, and the average value was taken.

[0052] (5) Capacitance change rate: Referring to IEC 60384-9 "Fixed capacitors for electronic equipment - Part 9: Class 2 multilayer ceramic fixed capacitors", the barium titanate ceramic product was made into a disc with a diameter of 10 mm and a thickness of 0.5 mm, with silver electrodes on both sides. The sample was placed in a high-temperature aging chamber at 150℃ and subjected to accelerated stress of 100V DC voltage for 1000 hours of durability testing. After the test, the capacitance value was measured at room temperature, and the capacitance change rate was calculated as (capacitance value after aging - initial capacitance value) / initial capacitance value × 100%. Three finished products were tested, and the average value was taken.

[0053] Table 2 Comparison of experimental results of Examples 1-3 and Comparative Examples 1-5 The experimental results of Examples 1-3 and Comparative Examples 1-5 are shown in Table 2 and Figure 5 , 6 As shown, the barium titanate ceramic product obtained by this invention exhibits comprehensive and excellent overall performance under completely rare-earth-free conditions: its dielectric constant is as high as 3041, while its dielectric loss is as low as 0.82%, achieving a balance between high energy storage and low loss; within a wide temperature range of -55℃ to 150℃, the maximum forward bias of the capacitor is +9.41%, and the maximum negative bias is -6.98%, with stability significantly better than the X5R standard; its insulation resistance at 125℃ reaches 8.03 × 10⁻⁶. 11 After 1000 hours of rigorous aging at 150℃ / 100V, its capacitance decreased by only -5.02%, which was determined to be the optimal implementation point.

[0054] Example 2, by reducing the doping amount, decreasing the BNF coating agent, and weakening the sintering and grain boundary reaction intensity, resulted in insufficient integrity and effectiveness of the in-situ generated h-BN-BaF2 composite grain boundaries. This reduced the grain boundaries' ability to "capture and block" oxygen vacancies, directly manifesting as a simultaneous decline in insulation resistance and anti-aging performance. Example 3, by increasing the doping amount, adding more BNF coating agent, and strengthening the sintering and grain boundary reaction intensity, aimed to further improve performance. However, data showed that while its dielectric constant and insulation resistance were better than Example 2, they did not surpass Example 1, and anti-aging performance showed a decline. This indicates that excessive enhancement of process parameters may have led to side reactions or microstructure imbalances.

[0055] Due to the lack of key technologies, the overall performance of Comparative Examples 1-5 was reduced to varying degrees compared to the Examples. Comparative Example 1, lacking Ca and Zr co-doping, failed to form a pre-strained crystal framework within the material, resulting in a significant increase in the temperature range and failure to meet the X5R standard. This result strongly demonstrates that Ca and Zr co-doping is an indispensable structural foundation for constructing high-dielectric, wide-temperature-stable material systems. Comparative Example 2 omitted the B, N, and F element coating steps, cutting off the material source for the entire in-situ grain boundary reaction. This directly resulted in the material failing to generate any h-BN-BaF2 composite grain boundary phase after sintering, with the grain boundaries reverting to ordinary high-defect states. The insulation resistance and capacitance change rate decreased significantly, and the dielectric properties and temperature stability also deteriorated simultaneously. This proves that BNF precursor coating is a necessary prerequisite for triggering the subsequent functionalized grain boundary formation, thereby fundamentally improving device reliability. Comparative Example 3 omitted the addition of a fluorine source during the preparation process, preventing the formation of a complete h-BN-BaF2 composite phase in the in-situ reaction. The grain boundaries severely lacked fluorine ions for effectively chemically anchoring oxygen vacancies. Although some B and N elements were retained, the insulation resistance and capacitance change rate were at the same inferior level as the completely uncoated Comparative Example 2, far from reaching the performance level of the embodiment. This confirms that F element is not an optional dopant, but an essential core component for constructing high-performance composite grain boundaries and realizing the chemical trapping function of oxygen vacancies. Without F, even with B and N, it is impossible to construct functional grain boundaries with high reliability. Comparative Example 4 did not use the self-made ZnO-B2O3-SiO2 low-temperature glass powder in the preparation process, which changed the densification temperature window of the material and may not be able to achieve sufficient sintering at 920℃, resulting in a decrease in microstructure uniformity. At the same time, the lack of the transition layer and pinning effect provided by this specific glass phase at the grain boundaries led to poor grain growth and grain boundary structure stability, which was directly reflected in its increased dielectric loss, deteriorated temperature stability, and significantly reduced insulation resistance. This comparative result proves that the self-made ZnO-B2O3-SiO2 low-temperature glass powder is not a general sintering aid, but rather a means to achieve low-temperature densification. The key functional components that regulate the microstructure of grain boundaries and match the BNF precursor and subsequent in-situ reactions were identified. Comparative Example 5 omitted the grain boundary engineering step of cooling to 850℃ and holding it at that temperature for 6 hours. As a result, the B, N, and F elements already present in the precursor could not undergo the designed in-situ chemical reaction at the grain boundary, thus failing to generate the h-BN-BaF2 composite grain boundary phase. The insulation resistance of the final material decreased significantly, proving that cooling-holding is the switch that actively triggers and completes the synthesis of functional grain boundaries.

[0056] In summary, this invention, through the innovative introduction of a boron-nitrogen-fluorine ternary synergistic doping system and the combination of a specific low-temperature co-firing process and controlled in-situ grain boundary reactions, successfully prepared a completely rare-earth-free barium titanate ceramic dielectric for X5R-type MLCCs. This dielectric dielectric can be co-fired with nickel electrodes at low temperatures and exhibits high dielectric constant, low loss, excellent temperature stability, and ultra-high reliability. Compared with existing technologies, this invention significantly reduces raw material costs, eliminates the dependence of high-performance MLCCs on rare-earth resources, and greatly improves the device's lifespan and reliability under high temperature and high pressure, demonstrating promising prospects for industrial production and a competitive advantage in the market.

Claims

1. A method for preparing boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs, comprising ceramic powder synthesis, green body fabrication, high-temperature sintering, end electrode fabrication and post-treatment, characterized in that, The synthesis of the ceramic powder consists of doped powder preparation and grinding reaction treatment. The doped powder preparation adopts a hydrothermal co-precipitation method. Based on the perovskite crystal structure, Ca is added during the early stage of crystal growth. 2+ Ions and Zr 4+ Ions are co-doped into the barium titanate lattice to construct a pre-strained lattice framework with intrinsic stress; the grinding reaction treatment is to prepare a core-shell structure precursor powder by cyclic grinding with the participation of multiple element additives. The core-shell structure is based on the doped powder as the core and the active layer of B, N, Ba and F elements anchored on the surface of the core by chemical bonds as the shell. The green fabrication process involves adding a glass phase additive during the preparation of the casting slurry; the high-temperature sintering process involves setting the sintering temperature to 900-950℃, and then holding the temperature at 800-900℃ before cooling down to form a composite phase of h-BN and BaF2 and insulating grain boundaries.

2. The preparation method of boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC as described in claim 1, characterized in that, The hydrothermal coprecipitation method specifically involves: using barium hydroxide octahydrate as the barium source, calcium hydroxide as the calcium source, tetrabutyl titanate as the titanium source, and tetrabutyl zirconate as the zirconium source, performing simultaneous hydrolysis and co-crystallization reactions in an alkaline hydrothermal environment under nitrogen protection to synthesize calcium / zirconium co-doped barium titanate nanopowder with a perovskite structure in one step; the multi-element additive is composed of triethyl borate, urea, and barium fluoride.

3. The preparation method of boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC as described in claim 1, characterized in that, The glass phase additive is composed of a ZnO-B2O3-SiO2 ternary system glass powder, wherein the mass ratio of each component is ZnO:B2O3:SiO2=47:31:

22.

4. The preparation method of boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC as described in claim 1, characterized in that, Includes the following steps: S1: Deionized water, ethanol, barium hydroxide octahydrate and calcium hydroxide were added to a container, heated and stirred; then tetrabutyl titanate and tetrabutyl zirconate were added dropwise at a uniform rate. After the addition was completed, the container was sealed, nitrogen was purged to replace the air, and then the temperature was raised and maintained; after the reaction was completed, the mixture was filtered and the filter cake was dried to obtain calcium / zirconium co-doped barium titanate nanopowder. S2: The obtained calcium / zirconium co-doped barium titanate nanopowder was circulated and ground with anhydrous ethanol, triethyl borate, urea, and barium fluoride; then the slurry was spray-dried, the inlet and outlet air temperatures were set, and the powder was collected after instantaneous drying to obtain a precursor powder uniformly coated with boron-nitrogen-fluorine. S3: The obtained boron-nitrogen-fluorine uniformly coated precursor powder, self-made zinc oxide barium oxide-silicon oxide low-temperature glass powder and organic casting aid are ball-milled and then vacuum degassed to obtain casting slurry; S4: The cast slurry is formed into a green strip, dried, and then the electrode pattern is printed and laminated. After isostatic pressing, the green chips are cut into blanks; the green chips are then debonded and densified in a protective atmosphere, followed by a controlled cooling-isothermal heat treatment process, and finally cooled to room temperature. After the end electrodes are prepared, the boron-nitrogen co-doped barium titanate ceramic product for X5R type MLCC is obtained.

5. The preparation method of boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC as described in claim 4, characterized in that, The mass ratio of barium hydroxide octahydrate and calcium hydroxide in S1 is 41.3~62; the mass ratio of tetrabutyl titanate and tetrabutyl zirconate is 26.6:35.5; the heating and heat preservation requires heating to 150~170℃.

6. The preparation method of boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC as described in claim 4, characterized in that, The mass ratio of triethyl borate, urea, and barium fluoride in S2 is 4:2:1 to 8:4:3; the set inlet and outlet air temperatures are wherein the inlet air temperature is set to 170 to 190°C.

7. The preparation method of boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC as described in claim 4, characterized in that, The self-made zinc oxide, barium oxide, and silicon oxide low-temperature glass powder and organic casting aid mentioned in S3 have a mass ratio of 3:57 to 8:83; the ball milling is set to a rotational linear velocity of 1 to 3 m / s and a revolution linear velocity of 4 to 6 m / s for 2 to 4 hours.

8. The preparation method of boron-nitrogen co-doped barium titanate ceramic for X5R type MLCC as described in claim 4, characterized in that, The densification sintering described in S4 requires heating to 900~950℃; the cooling-constant temperature heat treatment procedure is set to cool to 800~900℃ at a rate of 1~3℃ / min and hold at that temperature for 2~10 hours.

9. A boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs according to any one of claims 1 to 8, characterized in that, The boron-nitrogen co-doped barium titanate ceramic comprises the following components in parts by weight: 100 parts barium titanate, 45 parts deionized water, 35 parts anhydrous ethanol, 24.8 parts barium hydroxide octahydrate, 0.40-0.60 parts calcium hydroxide, 21.3 parts tetrabutyl titanate, 0.60-0.80 parts tetrabutyl zirconate, 0.70-1.50 parts multi-element additives, 0.3-0.8 parts glass phase additives, and 5.7-8.3 parts organic casting aids.

10. The boron-nitrogen co-doped barium titanate ceramic for X5R type MLCCs as described in claim 9, characterized in that, The barium titanate ceramic has a dielectric constant ≥ 2963, dielectric loss ≤ 0.87%, temperature-capacitance characteristic ≤ ±15%, and insulation resistance ≥ 6.21 × 10⁻⁶. 11 Ω and capacitance change rate ≥ -6.51%.

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