Fluorine insertion reactions of the brownmillerite materials Sr2Fe2O5, Sr2CoFeO5, and Sr2Co2O5

Abstract The brownmillerite structure provides an ordered vacancy lattice into which fluorine anions should easily be accommodated, with full occupation of the vacant sites resulting in a simple perovskite structure. Low-temperature fluorine insertion reactions with the brownmillerite Sr 2 Co 2 O 5 and related materials Sr 2 CoFeO 5 and Sr 2 Fe 2 O 5 have been investigated with a view to using fluorine insertion reactions to fill the oxygen vacancies in these materials, thus forming cubic perovskite-type phases with mixed 3+/4+ B cation oxidation states. The synthesis and magnetic properties of the new perovskite materials SrCoO 2.5 F 0.5 and SrCo 0.5 Fe 0.5 O 2.5 F 0.5 are presented here, supplemented by a consideration of Madelung energy calculations in order to explain the dissimilar fluorination behaviour of Sr 2 Fe 2 O 5 .