A novel approach to achieve high dielectric permittivity and low loss tangent in CaCu3Ti4O12 ceramics by co-doping with Sm3+ and Mg2+ ions

A novel strategy to improve the dielectric properties of CaCu3Ti4O12 ceramics was proposed by co-doping with Sm3+ and Mg2+. Sm3+ substituted in Ca2+ sites can effectively suppress the grain growth, achieving a fine grained ceramic microstructure. Mg2+ was selected to be substituted into Cu2+ sites to enhance the grain boundary (GB) resistivity for reducing the loss tangent (tanδ). High dielectric permittivity ϵ′ ≈ 1.25 × 104 and low tanδ ≈ 0.039 at 1 kHz were successfully accomplished in a Ca0.925Sm0.05Cu2.70Mg0.30Ti4O12 ceramic. Non-Ohmic properties were also enhanced. A slight increase in Ti3+/Ti4+ ratio in (Sm + Mg) co-doped CaCu3Ti4O12 ceramics was confirmed by the X-ray absorption near edge structure. Changes in tanδ values for all the co-doped ceramics were very consistent with their variations in GB resistance. The dielectric and non-Ohmic properties of co-doped ceramics were significantly improved by tuning both the geometric and intrinsic factors, i.e., increasing the density of GB layer and enhancing the GB resistance, respectively.