Frequency and temperature dependent dielectric and conductivity behavior of 0.95(K0.5Na0.5)NbO3–0.05BaTiO3 ceramic

Dielectric and conductivity measurements were carried out on the 0.95(K0.5Na0.5)NbO3–0.05BaTiO3 (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 Ba2+ and Ti4+ ions into the KNN lattice sites.

Research highlights▶ Frequency dependent conductivity of KNN–5BT exhibited a universal conductivity behavior. ▶ The activation energy for relaxation frequency is more than that for conduction. ▶ The high-temperature dielectric relaxation may be attributed to the formation of defect dipole.