Comment on the origin(s) of the giant permittivity effect in CaCu 3 Ti 4 O 12 single crystals and ceramics

Impedance spectroscopy has been performed on CaCu3Ti4O12 (CCTO) single crystals and ceramics using Au and InGa alloy electrodes. The extrinsic effect responsible for the giant permittivity observed at radio-frequencies near room temperature is shown to be different for single crystals and ceramics. For single crystals it is attributed to a non-ohmic electrode contact to semiconducting CCTO. For ceramics it is attributed to an internal barrier layer capacitor mechanism associated with semiconducting CCTO grains and insulating grain boundaries.