Magnetic exchange interactions in perovskite solid solutions. Part 7. A study of the non-stoicheiometric phase SrCoO3–y by 57Fe Mössbauer spectroscopy

Abstract

The non-stoicheiometric phase SrCoO_3–Y has been studied by Mössbauer spectroscopy using ⁵⁷Fe as an impurity probe, and by X-ray powder diffraction. The fully reduced phase Sr₂Co₂O₅ contains high-spin Co³⁺ in both octahedral and tetrahedral sites, and has the same magnetic spin arrangement as the analogous iron compound. Oxidation produces a poorly defined ‘hexagonal’ phase which is apparently non-magnetic even at 4.2 K. There is evidence to suggest that the structure of this phase is related to that of the brownmillerite lattice with the retention of layers of tetrahedrally co-ordinated Co³⁺, but with a high-spin to low-spin transition occurring on the octahedral sites. Slow relaxation effects have been observed for the iron impurities at low temperature, including a novel slow relaxation for Fe⁴⁺ ions.