Role of doping and CuO segregation in improving the giant permittivity of CaCu3Ti4O12

The dopant role on the electric and dielectric properties of the perovskite-type CaCu3Ti4O12 (CCTO) compound is evidenced. Impedance spectroscopy measurements show that the relevant permittivity value attributed to sintered CCTOis due to grain boundary (g.b.) effects. The g.b. permittivity value of the pure CCTOcan be increased of 1–2 orders of magnitude by cation substitution on Ti site and/or segregation of CuOphase, while the bulk permittivity keeps values 90o_ro180: Bulk and g.b. conductivity contributions are discussed: electrons are responsible for the charge transport and a mean bulk activation energy of 0.07 eV is obtained at room temperature for all the examined samples. The g.b. activation energy ranges between 0.54 and 0.76 eV. Defect models related to the transport properties are proposed, supported by electron paramagnetic resonance measurements.