Preparation and dielectric properties of X9R core–shell BaTiO3 ceramics coated by BiAlO3–BaTiO3

The typical “core–shell” structure in BT ceramics can easily obtain double dielectric anomalies, which greatly improve the dielectric temperature stability for multilayer ceramic capacitors. In this paper, BaTiO3 particles were coated with 0.3BiAlO3–0.7BaTiO3 shell [xBT@(0.3BA–0.7BT)] by a sol–gel method. Core–shell structure was proved to exist in ceramic grains by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). High-temperature X9R dielectrics were obtained when x=0.3 and 0.2, with a high dielectric constant (~1200) and low dielectric loss (<2.0%). Furthermore, the impedance data was fitted by an effective 4RC equivalent circuit, which could be assigned to the core, the shell, the grain boundary, and the ceramic/internal electrode interface regions. The activation energy of the core was found to decrease with x decreasing, while opposite tendency exists in the shell and the grain boundary.