Colossal dielectric constants: A common phenomenon in CaCu3Ti4O12 related materials

In the present work we demonstrate that in addition to the well-known colossal-dielectric-constant material CaCu3Ti4O12 various members of the series Ln2/3Cu3Ti4O12 with Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm also exhibit giant values of the dielectric constant. Just as CaCu3Ti4O12, all these materials show a Maxwell–Wagner type relaxation process. For the best material, Pr2/3Cu3Ti4O12, we provide a detailed investigation of its dielectric properties in a broad frequency range up to 1 GHz. Polarization at internal barriers, most likely grain boundaries, seems to be the reason for the observed very high values of the dielectric constant. Taking into account the present results and those reported in the literature, we conclude that CaCu3Ti4O12 is not exceptional at all and there seem to be various isostructural materials with similar dielectric properties.