Microstructures of X7R type base-metal-electroded BaTiO3 capacitor materials prepared by duplex-structured process

Low temperature coefficient of capacitance (TCC) for the MgO/Y2O3 co-doped BaTiO3 materials can be achieved by a duplex-structured process. The results of structure refinement reveal that large amount of MgO species can not only suppress the grain growth but increase the volume fraction of cubic phase of paraelectric BaTiO3 at room temperature. Investigations of transmission electron microscopy (TEM) indicate that the detailed microstructure is extremely complicated for the BaTiO3 materials. The heavily doped constituents of the samples remained as fine grains with paraelectric phase, whereas the lightly doped constituents of the materials grew, resulting in a core-shell microstructure via the incorporation of the MgO species when the mixture of the two constituents was sintered. The unique dielectric constant (K)–temperature (T) characteristics of the samples are ascribed to the duplex structure of the samples, which contain fine grains of cubic structure and large grains of core-shell structure.