Influence of sintering atmosphere on dielectric properties and microstructure of CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) ceramics were sintered in the mixed gases flow of O2 and N2 with different volume ratios by the solid state reaction method, the volume ratios were strictly controlled by a gas mixture proportioner during sintering. The effects of different volume fractions of O2 (x) on the microstructure and dielectric properties of CCTO ceramics were investigated. The appearance of Cu4O3 phase in the XRD patterns when x≥20%, suggests that a chemical reaction had occurred between Cu2O and O2. The Gibbs energy of formation of CCTO was closely related to the ternary phase relations of system CaO–CuO/Cu2O–TiO2, and the decrease of x promoted the decomposition of CCTO. All the samples showed high dielectric constant (≥5×103) in a broad frequency range from 20 Hz to 100 kHz, which decreased gradually with increasing x. Cole–Cole plots of conductivity suggested that the resistivity of grain and grain boundary both increased with increasing x. With the variation in the conductivity of grain boundary which is caused by the increasing x.