Order, Disorder, and Dynamics in Brownmillerite SrFeO.

The room-temperature structure of brownmillerite-type SrFeO remains controversial, despite numerous published crystallographic studies utilizing X-ray, neutron, and electron diffraction data collected on single-crystalline and powder samples. The main disagreements concern the ordering of twisted FeO tetrahedral chains within and between the layers stacked along the axis, and the impact of this ordering on oxide-ionic conductivity. Here, we present new data along with a reinterpretation of previously published diffraction images, including the reassignment of satellite reflections, which harmonize the results of past studies in a unified description of tetrahedral chain ordering in SrFeO at length scales relevant to X-ray and neutron diffraction. Implications for the prevailing model of oxide ion transport in this material are also discussed.