Novel oxygen vacancy-ordered phases of Ca2Fe2–xMnxO5prepared by the topotactic reduction of the perovskite oxides, Ca3Fe3–xMnxO9–y(0 < y < 1.5)

Octahedral (O), tetrahedral (T), and square pyramidal (SP) co-ordination polyhedra of the transition metal ions are shown to coexist in oxides of the type Ca2Fe2–xMnxO5; these oxides transform on heating to the brownmillerite structure with only O and T co-ordination polyhedra.