Effects of cation stoichiometry on the dielectric properties of CaCu3Ti4O12

Compositions based on CaCu3+xTi4+yO12 (x = +0.06, 0, −0.06; y = +0.08, 0, −0.08) with varying cation stoichiometry were prepared via the conventional solid state synthesis methods. No significant changes in the perovskite crystal structure were observed via diffraction compared to stoichiometric CaCu3Ti4O12 (CCTO). However, a CuO phase was detected on the surface of all compositions and the presence of Cu2O was observed in the inner region of the sample for both Cu- and Ti-excessive CCTO. From the results of dielectric measurements, Cu- and Ti-deficient CCTO showed a higher dielectric constant than undoped CCTO. Due to the presence of Cu2O, both Cu- and Ti-excessive CCTO yielded low values of the dielectric constant. Using impedance spectroscopy, the improvement in dielectric constants and low tan δ values in the Cu- and Ti-deficient CCTO compositions can be traced to the lower grain resistivities compared to stoichiometric CCTO.