AC behavior and PTCR effect in PZN-PT-BT ferroelectric ceramics

The ac behavior of the PZN-PT-BT ceramic system was studied in wide temperature and frequency ranges. Two contributions in the impedance plane were obtained: grain and grain-boundary responses. A positive temperature coefficient of resistivity (PTCR) was observed in the temperature dependence of the ceramic resistivity, dominated by the grain response. The results are explained on the basis of the Heywang and Jonker models. The Schottky barrier formed at grain boundary regions acts as traps of the electrons available from the oxygen vacancies in the ceramic, whose concentration decreases with temperature by an oxidation process when the temperature rises in air conditions, increasing the Schottky barrier height of the samples. This provides PTCR characteristics from the transition temperature to about 220 °C.