Ion transport in dual-phase SrFe1-xD cent D degrees O-x(3-delta) (x=0.03-aEuro parts per thousand 0.10): effects of redox cycling

The incorporation of tantalum cations in mixed-conducting SrFe1-xTaxO3-delta (x = 0.03 -aEuro parts per thousand 0.10) results in the formation of single cubic perovskite-like phases in oxidizing atmospheres while under reducing conditions phase separation is observed, accompanied with an appearance of brownmillerite-type nanodomains on the background of the perovskite-like matrix. For SrFe0.97Ta0.03O3-delta after reduction, the x-ray and electron diffraction studies combined with transmission electron microscopy evidence the formation of approximately 30 vol.% brownmillerite phase with an average domain size of 20-40 nm. The oxygen partial pressure dependencies of the total conductivity in the range from 10(-20) to 0.5 atm at 700-950 A degrees C show that the electron transport parameters remain virtually independent on the dopant content and domain structure. Contrary to the materials with higher dopant content, however, the ion conduction in SrFe0.97Ta0.03O3-delta tends to substantially increase on redox cycling. This behavior was attributed to the brownmillerite domain disintegration and rearrangement, induced by cyclic formation and disappearance of oxygen vacancies