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

Abstract

Reaction of the Ruddlesden–Popper phases Sr₂Fe_0.5Ru_0.5O₄ and Sr₃(Fe_0.5Ru_0.5)₂O₇ with CaH₂ results in the topochemical deintercalation of oxide ions from these materials and 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. Diffraction data reveal that both the <i>n</i> = 1 and <i>n</i> = 2 samples consist of two-phase mixtures of reduced phases with subtly different oxygen contents. The separation of samples into two phases upon reduction is discussed on the basis of a short-range inhomogeneous distribution of iron and ruthenium in the starting materials. X-ray absorption data and Mössbauer spectra reveal the reduced samples contain an Fe³⁺ and Ru^2+/3+ oxidation state combination, which is unexpected considering the Fe³⁺/Fe²⁺ and Ru³⁺/Ru²⁺ redox potentials, suggesting that the local coordination geometry of the transition metal sites helps to stabilize the Ru²⁺ centers. Fitted Mössbauer 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 data of both materials are consistent with spin glass-like behavior