The core-shell structure in ultrafine X7R dielectric ceramics

Based on a hydrothermal barium titanate powder, temperature stable dielectrics which meet the X7R specification were developed for the use of Multilayer Capacitors (MLCs). By establishing a chemical inhomogeneity within individual grains the ferroelectric to paraelectric transition peak is diffused and the material has a unique core-shell microstructure with a pure or lightly doped ferroelectric core and a highly doped paraelectric shell. As dielectric layers in MLCs decrease in size so does the grain size. This study investigates the sintering mechanism and core-shell structure in submicron grains.