Significantly improving the giant dielectric properties of CaCu3Ti4O12 ceramics by co-doping with Sr2+ and F- ions

Improved dielectric properties of CaCu3Ti4O12 ceramics were produced by co-doping with Sr2+/F- cation/anions. The grain sizes of the Ca1-xSrxCu3Ti4O12-xFx ceramics were considerably decreased, producing a large amount of insulating grain boundary (GB) layers. Optimized dielectric properties with a high dielectric permittivity of ε′∼6.44 × 104 and a low loss tangent (tanδ∼0.030) were produced. The non-Ohmic properties also improved. The Schottky barrier height (ΦB) of the GBs increased by co-doping with Sr2+/F- ions. The electrical properties of the semiconducting grains changed slightly. Accordingly, the increase in the total GB resistance (Rgb) significantly decreased the tanδ and increased the breakdown electric field. The increased Rgb resulted from the improved intrinsic properties of the GBs (that is, ΦB increased) and the controlled microstructure (that is, the insulating GB layers increased). The macroscopic giant dielectric and electrical properties were described using an internal barrier layer capacitor model related to the Schottky barrier height at the GBs.