Crystallographic and magnetic characterisation of the brownmillerite Sr2Co2O5

Sr2Co2O5 with the perovskite-related brownmillerite structure has been synthesised via quenching, with the orthorhombic unit cell parameters a=5.4639(3) Å, b=15.6486(8) Å and c=5.5667(3) Å based on refinement of neutron powder diffraction data collected at 4 K. Electron microscopy revealed L–R–L–R-intralayer ordering of chain orientations, which require a doubling of the unit cell along the c-parameter, consistent with the assignment of the space group Pcmb. However, on the length scale pertinent to NPD, no long-range order is observed and the disordered space group Imma appears more appropriate. The magnetic structure corresponds to G-type order with a moment of 3.00(4) μB directed along [1 0 0].

Possible ordering of the tetrahedral chains in Sr2Co2O5.Figure optionsDownload as PowerPoint slideResearch highlights
► Sr2Co2O5 has alternating (L and R) chains in a given tetrahedral layer.
► Order between layers is limited.
► NPD shows no evidence for the doubled unit cell-averaged structure.
► The length scale for a given technique is critical in considering space group.