A family of Sr-doped perovskite compounds Ln1−xSrxCoO3−δ (Ln = La3+, Pr3+ and Nd3+; x > 0.60), were prepared by sol–gel chemistry and reaction at 1100C under 1 atm of O. This structural family was shown to be present only for rare earth ions larger than Sm3+ and an upper limit of Sr2+ solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction exhibited oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction revealed that O vacancy ordering occurred, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln3+/Sr2+ cation ordering was observed.

Oxygen Vacancy Ordering in Strontium-Doped Rare Earth Cobaltate Perovskites, Ln1-xSrxCoO3-δ (Ln = La, Pr and Nd; x > 0.60). M.James, T.Tedesco, D.J.Cassidy, R.L.Withers: Materials Research Bulletin, 2005, 40[6], 990-1000