Aliovalent Ba2+ doping: A way to reduce oxygen vacancy in multiferroic BiFeO3

This paper demonstrates the impact of Ba2+ substitution on the structural, dielectric relaxation and AC conductivity properties of Bi1-x,BaxFeO3 (0 <= x <= 0.25) ceramics. Ba doping incorporates rhombohedral to tetragonal structural transformation in perovskite BFO. XPS data shows change in oxygen vacancy concentration with Ba doping and it also suggests that schoimetry of the doped compounds is not maintained by creating mix valance state of Fe. Reduction in oxygen vacancy (0Vs) in the doped samples is explained by Kroger-Vink notation. Arrhenius plot shows activation energy for dielectric relaxation of the doped samples lies between similar to 1.16 and 1.44 eV. AC conductivity of material decreases as Ba ion substitution increases in the parent compound. Electrical conductivity is attributed to the correlated barrier hopping (CBH) motion of the oxygen vacancies in the samples. Coulombic potential barrier (W-M) height, calculated from Elliott model for CBH motion of charge carriers shows correlation with the activation energy of AC conductivity at low temperature. Activation energy value obtained from the impedance measurements of the samples implies short range migration of oxygen vacancies dominates the frequency dependent conductivity while the frequency independent part of conductivity is the result of long range migration of oxygen vacancies. (C) 2015 Elsevier B.V. All rights reserved.