Dielectrics with high dielectric constant, low dielectric loss, and good temperature stability are essential for BaTiO₃-based MLCCs to meet the escalating demands of 5G communication technologies. However, challenges remain in further optimizing dielectric properties due to the correlation between these parameters. This study proposes a synergistic design strategy that overcomes this limitation through the coupling of compositional gradient control and nano-domain engineering. An optimized 900 ℃ pre-sintering process enables precise structural regulation, forming a tetragonal barium titanate core surrounded by a dopant-enriched graded compositional-gradient shell structure. Atomic-scale analysis confirms that the gradient design achieves directional distribution of Y/Mg/Mn dopants, stabilizes the highly tetragonal core, and confines oxygen vacancy-related defects to the shell region. This defect-localization effect suppresses long-range vacancy migration, thereby significantly enhancing insulation resistance and breakdown strength. Concurrently, the formation of relaxor-like polar nanodomains not only contributes to high dielectric constant but also optimizes the temperature stability of dielectric constant. Ultimately, the prepared ceramic materials exhibit a high dielectric constant (ε_r > 2200), excellent thermal stability meeting X8R standards (−55–150 ℃, ΔC/C_25℃ ≤ ±15%), and enhanced breakdown strength (> 6.7 kV/mm). This finding implies that the synergistic regulation of compositional gradients and nano-domain engineering may be a promising strategy for designing both high capacitance and robust reliability dielectric materials and provides a broad opportunity for the development of other dielectric materials.

As a highly reliable dielectric material, the study of BaTiO₃ ceramic grain boundary defects is very important for the reliability of multilayer ceramic capacitors (MLCC). In this paper, a series of amphoteric rare earth element Dy-doped BaTiO₃ ceramics (Dy: 0.2, 0.5, 1.0, 2.0, and 5.0 mol%) were prepared by the solid-phase method, and the effects of the defect types induced by the differences in the doping sites of the rare earth element Dy on the crystal-boundary defect of BaTiO₃ ceramics were investigated. The results indicate that ceramic doped with 0.2 mol% Dy₂O₃ exhibit a grain size of 330 nm, conductivity activation energy of 1.534 eV, grain boundary barrier of 0.4645 eV, bandgap of 3.193 eV, and oxygen vacancy concentration of 32.67 %. Notably, this composition demonstrates higher grain boundary activation energy and barrier potential among the investigated systems. The enhanced insulating properties of grain boundaries align with the stringent requirements for high-reliability dielectric materials. The defect analysis reveals that when Dy³⁺ doping is below 1.0 mol%, Dy³⁺ substitutes Ti⁴⁺ ions to form acceptor doping, generating oxygen vacancies as donor states. This increases carrier concentration within the system, reduces grain boundary activation energy and barrier potential, consequently diminishing impedance capability. In contrast, at Dy³⁺ concentrations exceeding 1.0 mol%, partial Dy³⁺ replaces Ba²⁺ to form donor doping, inducing barium vacancies due to charge compensation. These vacancies trap electrons, enhance effective acceptor states, and elevate grain boundary activation energy and barrier potential. This study demonstrates the significant role of grain boundary defects in the grain boundary barriers of rare earth doped BaTiO₃ ceramics, providing a way to achieve high reliability of BaTiO₃-based MLCCs.

As electronic devices continue to miniaturize, improving the dielectric performance and reliability of Multilayer Ceramic Capacitors (MLCC) during ultra-thin layer development has become a critical challenge. This study achieved significant optimization of BaTiO₃-based ceramic dielectric layers in ultra-thin MLCCs through precise control of the "core-shell" structure. Research shows that adjusting Ho doping concentration can effectively regulate the characteristics of the "core-shell" structure, thereby optimizing the dielectric performance and reliability indicators of MLCCs. When the Ho doping concentration reaches 1.5 mol%, the shell concentration increases significantly, and the material exhibits excellent dielectric properties: room temperature dielectric constant reaches 3820, dielectric loss remains below 2.0%, and demonstrates outstanding temperature stability with a temperature coefficient of capacitance not exceeding 15% within the -55 ℃ to 100 ℃ range. Notably, when Ho doping increases to 2 mol%, although the increased shell thickness leads to changes in the core-shell ratio resulting in slightly decreased dielectric performance, the material's insulation resistance improves significantly, enhancing overall reliability. This study systematically elucidates the structure-property relationships among Ho doping concentration, "core-shell" structural characteristics, and material performance, providing important theoretical guidance and experimental foundation for the structural design and performance optimization of ultra-thin MLCC dielectric materials. These findings hold significant scientific and practical value for advancing the development of next-generation high-performance MLCCs.

the development of X9R type (−55 to 200℃, ΔC/C_25℃≤ ±15%) high-performance ceramic dielectric materials has been accelerated by the advancement in high-capacity and high-temperature stability of Multilayer Ceramic Capacitors (MLCCs). In this study, the conventional solid-state reaction method was employed to systematically investigate the effects of the individual and synergistic doping of rare earth elements Dy and Ho on the phase structure, microstructure, and dielectric properties of 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃–0.02Nb₂O₅ ceramics. As a result, a wide-temperature stable X9R type BaTiO₃-based ceramic dielectric material was successfully prepared. The experimental results indicate that the ceramic grains of rare earth elements Dy and Ho exhibit a typical “core-shell” structure, demonstrating good temperature stability. The optimal dielectric performance is achieved at room temperature when Dy = 0.75 mol% and Ho = 0.25 mol% are synergistically doped, with the highest dielectric constant reaching 1725, and the temperature coefficient of capacitance (TCC, −55 ℃ ~200 ℃) ≤ 15%. The material 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃–0.02Nb₂O₅–0.75Dy₂O₃–0.25Ho₂O₃, with its high dielectric constant and excellent X9R type temperature characteristics, is a promising candidate for high-temperature MLCC applications.