Synthesis and characterization of Sr 1− xLnxCoO 3− δ, Ln=Y, Sm–Tm, 0.1⩽ x⩽0.5

Abstract

Different perovskite-related phases have been found in an X-ray powder diffraction (XRD) and transmission electron microscopy study of the Sr 1− x Ln x CoO 3− δ , Ln=Y, Sm–Tm, 0.1⩽ x⩽0.5 systems. For the compositions Sr 0.7Ho 0.3CoO 3− δ ; Sr 1− x Eu x CoO 3− δ , 0.3⩽ x⩽0.4; Sr 1− x Gd x CoO 3− δ , 0.3⩽ x⩽0.5; Sr 1− x Tb x CoO 3− δ , 0.3⩽ x⩽0.4; Sr 1− x Dy x CoO 3− δ , 0.2⩽ x⩽0.3 the formation of phases isostructural with the recently discovered perovskite related Sr 0.7Y 0.3CoO 2.62, a≈2× a per, c≈4× a per ( a per perovskite subcell) was observed. The crystal and magnetic structures of Sr 0.7Dy 0.3CoO 2.62 were refined using neutron diffraction data ( I4/ mmm, a=7.6280(8), c=15.338(2) Å, R p=0.0332, R F 2=0.0447, χ 2=1.19). For x=0.1 the XRD study indicates formation of cubic perovskites with all rare-earth cations. Electron diffraction and high resolution electron microscopy studies performed on Sr 0.9 Ln 0.1CoO 3− δ , Ln=Y, Eu, Dy, Ho revealed the presence of crystallites with brownmillerite ( a≈ 2 ×a per , b≈4× a per, c≈ 2 ×a per ), tetragonal perovskite ( a≈ a per, c≈2× a per) and Sr 0.7 Ln 0.3CoO 2.62 type ( a≈2× a per, c≈4× a per) structures. For Ln=Sm, only XRD cubic perovskite phases were observed for all compositions, 0.1⩽ x⩽0.5. In the Sr 0.5Eu 0.5CoO 3− δ sample, crystallites of perovskite, tetragonal perovskite and Sr 0.7 Ln 0.3CoO 2.62 type were observed in the TEM study.