Figure 1

(a) Observed (red dots), calculated (black line) and difference (bottom green line) patterns of SrFeO2.81, obtained using Lebail refinement of synchrotron X-ray powder diffraction data. Vertical check marks above difference profiles indicate Bragg reflections. Insets magnify selected pseudocubic reflections, (b) crystalline structure of SrFeO2.81; valence Fe4+ is attributed to Fe(1), Fe(3) and Fe3.5+ is attributed to Fe(2), based on previous work1, (c) FeO5 square pyramidal, (d) FeO6 distorted octahedra, and (e) FeO6 octahedra.