Crystal Structure of the Novel Complex Cobalt Oxide Sr_0.7Y_0.3CoO_2.62

The perovskite-related crystal structure of the compound Sr 0.7 Y 0.3 CoO 2.62 was determined and refined using synchrotron X-ray and neutron powder diffraction, in space group I 4/ mmm, a = 7.6237(8) Å and c = 15.314(2) Å, to R I = 0.041 in the synchrotron data set. It contains layers of CoO 6 octahedra, perpendicular to the c axis, alternating with partially disordered oxygen-deficient layers. Further characterization of the structure using electron diffraction and high-resolution electron microscopy showed that an additional superstructure was present in some of the crystallites. The structure represents a new type of layered ordering of oxygen vacancies in oxygen-deficient perovskites. Possible local atom arrangements in the oxygen-deficient layers and the structural relationship to the resembling brownmillerite-type structure for ABO 2.5 compounds are discussed.