Frequency and temperature dependent dielectric and conductivity behavior of 0.95(K 0.5Na 0.5)NbO 3–0.05BaTiO 3 ceramic

Abstract

Dielectric and conductivity measurements were carried out on the 0.95(K 0.5Na 0.5)NbO 3–0.05BaTiO 3 (KNN–5BT) ceramic both as a function of temperature (∼350–850 K) and frequency (40 Hz to 100 MHz). A high-temperature dielectric relaxation above Curie temperature (∼590 K) was observed and analyzed with the Cole–Cole function. Frequency dependent conductivity was analyzed with an augmented Jonscher relation and exhibited a universal conductivity behavior. The activation energy of dielectric relaxation was estimated to be 1.09 eV. It could be attributed to the thermal motion of double ionized oxygen vacancy or to the formation of defect dipoles between the acceptor ion and charge compensating oxygen vacancies. The mechanism for both the high-temperature dielectric relaxation and the frequency dependent conductivity was proposed based on a possible mode of incorporation of Ba 2+ and Ti 4+ ions into the KNN lattice sites.