The Mixed Electronic and Ionic Conductivity of Perovskite-Like Ba1-xSrxFe1-yTiyO3-δ and BaTi0.5Fe0.5-zCezO3-δ Solid Solutions

The work is focused on the studying of structural peculiarities, electronic and ionic conductivity, and thermomechanical properties of perovskite-like compositions in Ba1 -xSrxFe1 -yTiyO3 - delta and BaTi0.5Fe0.5 -zCezO3 - delta systems. The cubic structure was shown to be preserved on the substituting of up to 50% of barium cations for strontium in A-sublattice of (Ba,Sr)(Fe,Ti)O3 - delta, while further doping leads to transition of the crystal lattice into its hexagonal modification. The introducing of Ce into the B-sublattice suppressed this transformation to some extent. Substitution of titanium or cerium for iron reduced both electronic and ionic conductivity, due to the lowering of concentration of the sites available for electron transfer in the B-sublattice, lower oxygen nonstoichiometry, and larger Ti-O and Ce-O bond energy, as compared to that for Fe-O. Generally, the stabilization of the cubic structure ensures larger mobility of electronic and especially ionic charge carriers. The increasing of Ba content in the (Ba,Sr)(Fe,Ti)O3 - delta perovskite with cubic structure improved its ionic conductivity and resulted in an elongation of Fe-O bond and decreasing of the degree of overlapping between iron and oxygen atoms, which leads to lower electronic conductivity. The thermal expansion coefficients correlate with the ionic conductivity; the minimum expansibility was observed for the Ba-enriched compositions with hexagonal structure. It was demonstrated that the oxygen permeability of the (Ba,Sr)(Fe,Ti)O3 - delta and Ba(Fe,Ti,Ce)O3 - delta dense membranes is limited by the oxygen diffusion in the membrane phase bulk and the oxygen surface-exchange kinetics.