Structural and Mössbauer study of the Brownmillerite oxides LaSrMn2−xFexO5 (0 ⩽ x ⩽ 0.5)

Iron doped brownmillerite oxides LaSrMn2−xFexO5 (0 ⩽ x ⩽ 0.5) have been prepared as pure powders by a conventional solid state reaction and studied by X-ray powder diffraction, scanning electronic microscope and Mössbauer spectroscopy. Rietveld analysis of X-ray diffraction patterns confirms that all samples crystallize in the orthorhombic system with Pnma space group and are isotypic with the Ca2Fe1.039Mn0.962O5 phase. Cell parameters and crystallite size show an anomaly around x = 0.2 which is explained by the partial substitutions of Mn2+ and Mn3+ by Fe3+ and small amounts of Fe4+. A detailed analysis of the Mössbauer spectra for all compounds measured at room temperature shows that Fe3+ ions are located in distorted octahedral and tetrahedral sites. The environment and oxidation states of Mn and Fe are determined by bond valence sum calculations and the results for Fe are compared to the results from the Mössbauer study.