Influence of defects on the dielectric relaxation and electrical conductivity behavior for Sr0.70Ba0.30Bi2Nb2O9 ferroelectric ceramic

Sr0.7Ba0.3Bi2Nb2O9 ferroelectric ceramic system is studied concerning the dielectric relaxation and electrical conductivity processes in wide temperature and frequency ranges. The dielectric relaxation analysis is carried out by using the Cole-Cole model and the Universal Relaxation Law. From the activation energy value for the relaxation time, the dielectric relaxation processes at low temperatures (T < 90 °C) has been associated to polarons. For temperatures between 90 °C and 300 °C the contribution of polarons increases and the dielectric parameters follow the Universal Relaxation Law. From 300 °C to 450 °C, a strong influence of the electrical conductivity in the dielectric relaxation processes has been observed. The frequency dependence of the electrical conductivity was analyzed by using the Universal Dielectric Response (UDR) model. The electrical conductivity processes have been related to the presence of polarons in correspondence with the dielectric analysis for temperatures below 300 °C. For temperatures above 300 °C the main contribution to both dielectric relaxation and electrical conductivity is the hopping of electrons from the ionization of oxygen vacancies.