Effect of MnO2 addition on structure, electrical and optical properties of Ba(Fe0.5Nb0.5)O3 ceramics

Admixture of Ba(Fe0.5Nb0.5)O3 (BFN) ceramics with different content of MnO2 (0, 0.5, 1.0, 1.5 and 2.0 wt.%) powder were processed through conventional solid-state reaction route. The XRD characterization of all sintered samples confirmed the formation of a single cubic perovskite structure.MnO2 acts as sintering aid, which significantly enhances grain size of the BFN ceramics. The room temperature dielectric constant and conductivity of the MnO2 modified BFN ceramics were suppressed compared to the pure BFN ceramics. However, the dielectric constant increases with the increase in temperature above 250 ?C. The relaxation activation energy (>0.6 eV) and high dielectric constant (?104 at temperature above 250 ?C) of the MnO2 modified BFN ceramics were explained on the basis of ionization of oxygen vacancies, mobile oxygen vacancies and polaron hopping between multiple oxidation states of manganese (Mn2+ and Mn3+). A narrow band gap of 1.45 eV was observed in the 1.5 wt.% MnO2 modified BFN ceramics.