Phenomenological model of grain boundary behaviour under a bias field in Nb-doped CaCu3Ti4O12 ceramics

► We study the dielectric behaviour and capacitance-voltage (C-V) curves under an applied DC bias field of 1 wt% Nb-doped CaCu3Ti4O12 ceramics. ► There are grain boundaries of different electrical nature. ► At low frequency the material exhibits a double Metal Oxide Semiconductor (MOS) capacitor-like behaviour. ► At higher frequency the C-V curve suffers an inversion showing a ferroelectric-like response. ► The giant dielectric constant is not intrinsic to the material but apparent and it is caused by conduction effects.