Single phase perovskite-type oxides La0.2Sr0.8FeO3-Delta (LSF28) and La0.4Sr0.6FeO3-Delta (LSF46) were prepared by the glycine nitrate process. The oxygen nonstoichiometry of LSF46 was studied by precision thermogravimetry at 700 and 900 degrees C as a function of oxygen partial pressure. Mossbauer spectra were measured at room temperature, as well as at 500 and 700 degrees C (LSF28) and at 700 and 900 degrees C (LSF46) under varying oxygen partial pressures. Good agreement is observed for the pO(2)-dependent nonstoichiometry of LSF46 at 700 and 900 degrees C as derived from thermogravimetry and in-situ Mossbauer spectroscopy. At low pO(2), the Mossbauer isomer shifts and quadrupole splittings indicate a phase transition in LSF46 at 700 degrees C and in LSF28 at the two temperatures studied from a disordered perovskite phase to a brownmillerite-like structure with larger quadrupole splitting. (c) 2006 Elsevier B.V. All rights reserved.