Formation mechanism of core–shell structures in Mg-doped BaTiO ₃ -based ceramics for high-temperature MLCCs application

Enhancing the thermal stability of dielectric ceramics is crucial for maintaining the reliability of multilayer ceramic capacitors (MLCCs) under fluctuating thermal environments. While core–shell structuring has proven effective in mitigating temperature-dependent permittivity variations, the role of dopant chemistry in governing its formation and associated dielectric stability remains insufficiently understood. In this study, 0.9BaTiO 3 –0.1(Bi 0.5 Na 0.5 )TiO 3 ceramics co-modified with 2.0 mol% Nb 2 O 5 were fabricated via a conventional solid-state method, and different amounts of MgO or MgCO 3 were introduced to systematically investigate the effects of dopant chemistry and incorporation behavior on the microstructure and dielectric properties. Comparative structural analysis revealed that MgO and MgCO 3 exhibited significantly different influence on core–shell structure evolution. MgO, due to its high reactivity and rapid diffusion during sintering, facilitated compositional homogenization and impeded the formation of distinct core–shell structures, thereby leading to a deteriorated temperature coefficient of capacitance (TCC). In contrast, MgCO 3 decomposed progressively during sintering, allowing for delayed and controlled incorporation of Mg 2+ ions, which promotes the development of well-defined core–shell architectures and preserves compositional gradients within grains. As a result, only the MgCO 3 -doped ceramics satisfied the X9R specification, exhibiting excellent dielectric thermal stability over the temperature range of −55 to 200 °C. These results highlight the importance of dopant chemistry and diffusion behavior in controlling core–shell structures and enhancing the thermal stability of lead-free ceramics for high-temperature MLCCs applications.