Improvement of breakdown field and dielectric properties of CaCu3Ti4O12 ceramics by Bi and Al co-doping

Bi and Al co-doped CaCu3Ti4O12 (CCTO) ceramics with different doping concentration were fabricated by the solid-state sintering method. Great enhancements in dielectric and varistor properties of CCTO ceramic were achieved by co-doping at the concentration of 1 mol%. It is found that grain size distribution of co-doped sample is more uniform and the grain alignment is more compact. The improved morphologies could facilitate the macroscopic properties. Additionally, a relaxation peak, of activation energy at 0.39 eV, at relatively low frequency was characterized. It is likely to be originated from Cu-rich phase related defect in the grain boundary. This defect may be concomitantly aggravated by Bi and Al co-doping. The frequency dependence of the conductivity was interpreted with the Jonscher's law, indicating that the dc conduction loss at low frequency can be suppressed by additives. Comparing with the pure CCTO, the breakdown field Eb of co-doped sample at the concentration of 1 mol% was greatly enhanced from 2088 V/cm to 7839 V/cm due to the increase of Schottky barrier height (from 0.56 eV to 0.72 eV).