Defect-assisted core-shell control in rare-earth-doped BaTiO3 ceramics for high reliability BME MLCCs

This work investigates the microstructure, defect chemistry, internal stress distribution, and reliability of Y–Yb co-doped BaTiO 3 ceramics, in comparison with Y–Er co-doped counterparts. STEM–EDS reveals stronger grain-boundary segregation of Yb-containing species, forming core–shell structures. GPA further shows that lattice distortion is strongly localized within these dopant-rich shells, whereas grain cores remain comparatively relaxed. In contrast to the weakly bound A-site defect chemistry of Er, Y–Yb co-doping is associated with the formation of rare-earth (RE)–oxygen-vacancy-related defect centers likely involving both Ba and Ti sites, inducing a strongly distorted dopant-rich shell that effectively suppresses oxygen-vacancy migration and significantly enhances grain-boundary insulating behavior. Accordingly, Y–Yb co-doped compositions exhibit longer lifetime and improved reliability, with the optimized Yb2 sample showing an approximately 2.2-fold increase in mean time to failure (MTTF) compared to the baseline sample (Yb0), while compositions with moderate Yb content achieve the best combination of high breakdown strength (12.78 kV·mm⁻¹) and superior DC-bias stability. Overall, these findings identify moderate Y–Yb co-doping as an effective route to achieving a balanced improvement in permittivity, reliability, and miniaturization capability in next-generation high-reliability BME-MLCC materials.