Atomic ordering in the doped rare earth cobaltates Ln0.33Sr 0.67CoO 3− δ ( Ln=Y 3+, Ho 3+ and Dy 3+)

Abstract

The perovskite-based rare earth cobaltates ( Ln 0.33Sr 0.67CoO 3− δ ) ( Ln=Y 3+, Ho 3+ and Dy 3+) have been synthesized at 1100°C under 1 atm oxygen. A thermogravimetric study has determined the overall oxygen content in each case while a combined electron diffraction (ED) and synchrotron X-ray diffraction study has revealed the presence of a complex, previously unreported, perovskite-related superstructure phase. ED gave a resultant C1 c1 but most probably Cmcm ( a =2a p −2c p , b =4b p , c =2a p +2c p ) perovskite-related superstructure, describable as a modulated I4/ mmm intermediate parent structure. Synchrotron X-ray data has been used to refine the intermediate parent structures of all three compounds. Coupled Ln/Sr and O/vacancy ordering and associated structural relaxation is shown to be responsible for the observed superstructure.