Giant permittivity and Maxwell–Wagner relaxation in Yb : CaTiO₃ceramics

Abstract

Yb-modified CaTiO3 ceramics sintered for 24 h at 1450 °C exhibit a giant apparent permittivity of about 104 with a remarkable temperature (30–300 K) and frequency (101–106 Hz) stability (maximum variation: ±20%). After a post-annealing treatment of 48 h at 1100 °C, the dielectric response is strongly modified, with a high frequency, low temperature permittivity corresponding to the intrinsic dielectric behaviour of CaTiO3. A step-like rise in the apparent permittivity and a complex dielectric behaviour is observed with increasing temperature. The overall dielectric response of the ceramics can be interpreted in terms of the Maxwell–Wagner interfacial relaxation and modelled using equivalent circuits. The analysis demonstrates that the as-sintered ceramic consists of semiconducting grains (resistivity <104 Ω cm at 300 K) and insulating grain boundaries (resistivity ≈107 Ω cm at 300 K). Partial reoxidation takes place during post-annealing with the formation of oxygen gradients and increased electrical heterogeneity. In general, the dielectric response will be determined by the extent of the reoxidation reaction during cooling or post-annealing treatment below the sintering temperature.