In-situ Mössbauer spectroscopy and thermogravimetry of La0.2Sr0.8FeO3−Δ and La0.4Sr0.6FeO3−Δ

Single phase perovskite-type oxides La_0.2Sr_0.8FeO_3−Δ (LSF28) and La_0.4Sr_0.6FeO_3−Δ (LSF46) were prepared by the glycine nitrate process. The oxygen nonstoichiometry of LSF46 was studied by precision thermogravimetry at 700 and 900 °C as a function of oxygen partial pressure. Mössbauer spectra were measured at room temperature, as well as at 500 and 700 °C (LSF28) and at 700 and 900 °C (LSF46) under varying oxygen partial pressures. Good agreement is observed for the pO₂-dependent nonstoichiometry of LSF46 at 700 and 900 °C as derived from thermogravimetry and in-situ Mössbauer spectroscopy. At low pO₂, the Mössbauer isomer shifts and quadrupole splittings indicate a phase transition in LSF46 at 700 °C and in LSF28 at the two temperatures studied from a disordered perovskite phase to a brownmillerite-like structure with larger quadrupole splitting.