Colossal breakdown electric field and dielectric response of Al-doped CaCu3Ti4O12 ceramics

A greatly enhanced breakdown electric field of ∼21 kV/cm was achieved by liquid-phase doping of Al2O3 in CaCu3Ti4O12 (CCTO) ceramics. It was found that the dielectric loss of CCTO ceramics was composed of two dielectric relaxation peaks and dc conduction. Impedance analysis showed that the grain boundary resistance was increased from 0.37 MΩ to 13.55 MΩ and the corresponding activation energy of grain boundary was elevated from 0.63 eV to 0.81 eV. The frequency dependence of the conductivity was interpreted with the Jonscherʹs law, which indicated that the contribution of dc-like conduction at low frequency was effectively suppressed by Al2O3 doping. In addition, dimensional effect of the CCTO ceramics was found and an inflection (or critical) point behavior can be observed for pure and Al-doped samples, which referred to the variation of the breakdown electric field with the thickness of the samples.