Non-Ohmic and dielectric properties of Ba-doped CaCu3Ti4O12 ceramics

The microstructure, dielectric and electrical properties of Ca_1?x Ba _x Cu₃Ti₄O₁₂ (where x = 0, 0.025, and 0.05) ceramics were investigated. Our microstructural analyses revealed that Ba²⁺ doping ions preferentially form in a secondary phase, and are not introduced into the CaCu₃Ti₄O₁₂ lattice. Grain growth rate of CaCu₃Ti₄O₁₂ ceramics was significantly inhibited by the Ba-related secondary phase particles, resulting in a large decrease in their mean grain size. The dielectric permittivity of CaCu₃Ti₄O₁₂ ceramics decreased with increasing Ba content. Their loss tangent decreased after addition of CaCu₃Ti₄O₁₂ with 2.5 mol% of Ba²⁺, and increased with increasing Ba contents to 5.0 mol%. The nonlinear coefficient and breakdown field of the Ca_1?x Ba _x Cu₃Ti₄O₁₂ ceramics were significantly enhanced by adding 2.5 mol% of Ba²⁺, followed by a slight decrease as Ba²⁺ concentration was increased to 5.0 mol%. Using impedance spectroscopy analysis, it was revealed that variations in dielectric and non-Ohmic properties are associated with electrical response of grain boundaries. This supports the internal barrier layer capacitor model.