Enhanced non-Ohmic properties and giant dielectric response of (Sm plus Zn) co-doped CaCu3Ti4O12 ceramics

The non Ohmic and giant dielectric properties of CaCu3Ti4O12 and Ca0.925Sm0.05Cu3-xZnxTi4O12 (x = 0.0-0.10) ceramics prepared by a modified sol-gel method were studied. Influences of (Sm+Zn) co-dopants on the crystalline structure and microstructure of CaCu3Ti4O12 ceramics were investigated. The lattice parameter value was slightly enhanced, while the grain size was greatly reduced by inclusion of (Sm+Zn) co-dopants. Interestingly, the dielectric loss tangent in the frequency range of 10(2)-10(6) Hz was significantly reduced (tan delta approximate to 0.041 at 1 kHz), whereas the dielectric permittivity was still too large (> 10(3)). Furthermore, their nonlinear electrical properties were significantly enhanced. The nonlinear coefficient and breakdown electric field increased with increasing co-dopant concentration. The conduction activation energies of the grain and grain boundaries slightly changed, while the grain boundary resistance was greatly increased corresponding to a reduction in the mean grain size. The variations in giant dielectric and nonlinear electrical properties can be well described by the internal barrier layer capacitor effect.