Thermostimulated current, dielectric and EPR studies of the paraelectric phase of Ni-doped barium-strontium titanate ceramics

In order to understand the effect of the acceptor doping in perovskite type ceramics, dielectric properties of Ni-doped (Ba,Sr)TiO3 ceramics have been studied with the aid of Thermo-Stimulated Current (TSC) and Electron Paramagnetic Resonance (EPR). Dielectric properties of these ceramics doped up to 2% of nickel show an anomaly of epsilon around 250°C (paraelectric phase) depending strongly on the measurement frequency. The TSC studies suggest that this phenomenon is mainly due to dielectric rotation of impurity-vacancy dipoles localized on each grain surface. EPR measurements show that existence of Ni2+ and Ni3+ cations in the perovskite matrix, which implies the existence of Ni-Ti-Vo¯ dipole with oxygen vacancy introduced to compensate the charge excess.