CaCu3Ti4O12 ceramics substituted by Mg for Ca were prepared by the solid state reaction method. The crystal structures, microstructures, and dielectric properties of the Ca1-xMgxCu3Ti4O12 ceramics were investigated. At lower doping concentrations, the substitution of Mg for Ca caused a decreased lattice constant, while at higher doping concentrations, some of the Mg dopants started to replace Ti and resulted in an increased lattice constant, and some could also replace Cu due to the similar ion radius between Mg and Cu ions. Mg doping was found to promote the grain growth of Ca1-xMgxCu3Ti4O12 ceramics during sintering. Grain boundary resistance of the Ca1-xMgxCu3Ti4O12 ceramics was found to be increased by Mg doping. Enhanced dielectric properties was observed in the Ca1-xMgxCu3Ti4O12 ceramics with x=0.05 for the frequency range from 1 kHz to 20 kHz. For other doping concentrations, the dielectric losses of Ca1-xMgxCu3Ti4O12 ceramics were generally lowered.
