Abstract
Crystal structure, short range order, lattice dynamics and valence state of polycrystalline single-phase strontium ferrites SrFeO3-δ (with 3–δ = 2.87 ÷ 2.5) were studied by Raman and Mössbauer spectroscopy at normal conditions. Valence states of Fe ions and their fractions were determined from Mössbauer spectroscopy and concentrations of oxygen in all phases were estimated. For all studied SrFeO3-δ phases only five (or less) bands were observed above 200 cm−1 in spite of numerous Raman active phonon modes predicted by a factor group analysis. For the antiferromagnetic Brownmillerite phase (3–δ = 2.5), a broad band observed at ∼ 1350-1400 cm−1, was attributed to the two-magnon scattering. This band was found also for the SrFeO3-δ samples with 3–δ = 2.87 ÷ 2.725 which are in paramagnetic state at room temperature. This fact indicates an existence of the unusual magnetic correlations in all SrFeO3-δ perovskites.
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