In this work, the influence of starting particle size and sintering conditions on the microstructures and dielectric properties of BaTiO3-based ceramics coated with 0.3Bi(Zn1/2Ti1/2)O-3-0.7BaTiO(3) were investigated to reveal the core-shell structure by using high resolution transmission electron microscopy technique coupled with energy-dispersive spectrometer analysis. The ion-diffusion behavior plays a critical role in the formation and evolution of the core-shell structure and, therefore, significantly influences the dielectric properties. When using starting powders containing BaTiO3 particles larger than 100 nm in size and sintering for shorter dwelling times (0.5-2.0 hours), a core-shell structure could be formed and retained owing to the limited diffusion behavior, enabling BaTiO3-based ceramics to meet the X8R specification for multilayer ceramic capacitors applications at high temperatures. However, when using 80 nm BaTiO3 nanopowders and further extending the dwelling time to 6.0 hours, more driving energy was provided to prompt ion diffusion, which led to the compositional inhomogeneity becoming homogenized.