Electrical properties and microstructural characteristics of nonstoichiometric CaCu_3xTi₄O₁₂ ceramics

The influence of copper on the microstructure, electrical properties, resistances of grain and grain boundary of nonstoichiometric CaCu_3xTi₄O₁₂ ceramics, with x = 0.8, 0.9, 1.0, 1.1 and 1.2) prepared by solid state reaction were investigated. The second phase TiO₂ and CaTiO₃ are found in copper deficiency samples while CuO appears in the other samples. The grain size changes dramatically with the increase of copper. Frequency dependence dielectric permittivity exhibits that the deficient and excess of copper promote to a decrease of dielectric permittivity. Impedance complex plane shows both copper deficient and copper excess result in the increases of resistances of grain, grain boundary and contact resistance between electrode and ceramics.