Atomic ordering in the doped rare earth cobaltates Ln0.33Sr0.67CoO3-δ (Ln = Y3+, Ho3+ and Dy3+)

The perovskite-based rare earth cobaltates (Ln(0.33)Sr(0.67)CoO(3-delta)) (Ln = Y3+, Ho3+ and Dy3+) have been synthesized at 1100degreesC 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 C1c1 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. (C) 2003 Elsevier Science (USA). All rights reserved.