Small-moment paramagnetism and extensive twinning in the topochemically reduced phase Sr2ReLiO5.5

Abstract

Reaction of the cation-ordered double perovskite Sr₂ReLiO₆ with dilute hydrogen at 475 °C leads to the topochemical deintercalation of oxide ions from the host lattice and the formation of a phase of composition Sr₂ReLiO_5.5, as confirmed by thermogravimetric and EELS data. A combination of neutron and electron diffraction data reveals the reduction process converts the –Sr₂O₂–ReLiO₄–Sr₂O₂–ReLiO₄– stacking sequence of the parent phase into a –Sr₂O₂–ReLiO₃–Sr₂O₂–ReLiO₄–, partially anion-vacant ordered sequence. Furthermore a combination of electron diffraction and imaging reveals Sr₂ReLiO_5.5 exhibits extensive twinning – a feature which can be attributed to the large, anisotropic volume expansion of the material on reduction. Magnetisation data reveal a strongly reduced moment of μ_eff = 0.505μ_B for the d¹ Re⁶⁺ centres in the phase, suggesting there remains a large orbital component to the magnetism of the rhenium centres, despite their location in low symmetry coordination environments.