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−δ were studied. The oxygen permeation through strontium ferrite–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 Sr0.97(Ti,Fe)O3−δ leads to a considerable increase in oxygen ionic and electronic conductivities, and thermal expansion. The ion transference numbers of Sr0.97Fe0.80Ti0.20O3−δ 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 4×10−3 to 1.5×10−2 at 973–1223 K, decreasing with reducing temperature. The oxygen ionic conductivity of Sr0.97Fe0.80Ti0.20O3−δ is close to the conductivity of the Zr0.92Y0.08O1.96 solid electrolyte. The average thermal expansion coefficient of strontium ferrite–titanate, calculated from dilatometric data, is (13.8±0.1)×10−6 K−1 at 300–780 K and (27.0±0.4)×10−6 K−1 at 780–1040 K.