Topochemical\nReduction of the Ruddlesden–Popper Phases Sr₂Fe_0.5Ru_0.5O₄ and Sr₃(Fe_0.5Ru_0.5)₂O₇

Abstract

Reaction\nof the Ruddlesden–Popper phases Sr₂Fe_0.5Ru_0.5O₄ and Sr₃(Fe_0.5Ru_0.5)₂O₇ with CaH₂ results\nin the topochemical deintercalation of oxide ions from these materials\nand the formation of samples with average compositions of Sr₂Fe_0.5Ru_0.5O_3.35 and Sr₃(Fe_0.5Ru_0.5)₂O_5.68, respectively.\nDiffraction data reveal that both the <i>n</i> = 1 and <i>n</i> = 2 samples consist of two-phase mixtures of reduced phases\nwith subtly different oxygen contents. The separation of samples into\ntwo phases upon reduction is discussed on the basis of a short-range\ninhomogeneous distribution of iron and ruthenium in the starting materials.\nX-ray absorption data and Mössbauer spectra reveal the reduced\nsamples contain an Fe³⁺ and Ru^2+/3+ oxidation\nstate combination, which is unexpected considering the Fe³⁺/Fe²⁺ and Ru³⁺/Ru²⁺ redox potentials,\nsuggesting that the local coordination geometry of the transition\nmetal sites helps to stabilize the Ru²⁺ centers. Fitted\nMössbauer spectra of both the <i>n</i> = 1 and <i>n</i> = 2 samples are consistent with the presence of Fe³⁺ cations in square planar coordination sites. Magnetization\ndata of both materials are consistent with spin glass-like behavior.