Atmosphere controlled conductivity and Maxwell-Wagner relaxation in Bi0.5K0.5TiO3 – BiFeO3 ceramics

Abstract

Here, we report on a giant dielectric relaxation in (1 x)Bi0.5K0.5TiO3—xBiFeO3 ceramics below 300 C, which becomes more pronounced with increasing BiFeO3 content. The relaxation was shown to be of Maxwell-Wagner type and associated with charge depletion at the electroded interfaces. It was also shown that the relaxation could be controlled or, eventually, removed by heat treatment in controlled partial pressure of oxygen. This was rationalized by the relationship between the electrical conductivity and variation in the oxidation state of Fe, which is strongly coupled to the partial pressure of oxygen. The results are discussed with emphasis on oxygen diffusion and point defect equilibria involving oxygen vacancies and iron in divalent and tetravalent state. Finally, the barrier-free dielectric properties of the (1 x)Bi0.5K0.5TiO3—xBiFeO3 ceramics are reported.