Oxygen ionic conductivity of Ti-containing strontium ferrite

The total electrical conductivity, oxygen permeability, Faradaic efficiency and thermal expansion of perovskite-type Sr0.97Fe0.80Ti0.20O3-delta were studied. The oxygen permeation through strontium fenite-titanate ceramics was found to be limited by both bulk ionic conduction and surface exchange rates, similar to other Fe- and Ti-containing perovskites. Increasing iron content in the system Sr-0.97(Ti,Fe)O3-delta leads to a considerable increase in oxygen ionic and electronic conductivities, and thermal expansion. The ion transference numbers of Sr0.97Fe0.80Ti0.20O3-delta were determined by the Faradaic efficiency measurements, and estimated from the oxygen permeability data. Typical values of the transference numbers vary in the range from 4 X 10(-3) to 1.5 X 10(-2) at 973-1223 K, decreasing with reducing temperature. The oxygen ionic conductivity of Sr0.97Fe0.80Ti0.20O3-delta is close to the conductivity of the Zr0.92Y0.80O1.96 solid electrolyte. The average thermal expansion coefficient of strontium ferrite-titanate, calculated from dilatometric data, is (13.8+/-0.1)X 10(-6) K-1 at 300-780 K and (27.0+/-0.4) x 10(-6) K-1 at 780-1040 K. (C) 2000 Published by Elsevier Science B.V.