Synthesis and characterization of Sr1$minus;xLnxCoO3$minus;$delta;, Ln=Y, Sm?Tm, 0.1$les;x$les;0.5

Abstract

Different perovskite-related phases have been found in an X-ray powder diffraction (XRD) and transmission electron microscopy study of the Sr1−xLnxCoO3−δ, Ln=Y, Sm–Tm, 0.1⩽x⩽0.5 systems. For the compositions Sr0.7Ho0.3CoO3−δ; Sr1−xEuxCoO3−δ, 0.3⩽x⩽0.4; Sr1−xGdxCoO3−δ, 0.3⩽x⩽0.5; Sr1−xTbxCoO3−δ, 0.3⩽x⩽0.4; Sr1−xDyxCoO3−δ, 0.2⩽x⩽0.3 the formation of phases isostructural with the recently discovered perovskite related Sr0.7Y0.3CoO2.62, a≈2×aper, c≈4×aper (aper perovskite subcell) was observed. The crystal and magnetic structures of Sr0.7Dy0.3CoO2.62 were refined using neutron diffraction data (I4/mmm, a=7.6280(8), c=15.338(2) Å, Rp=0.0332, RF2=0.0447, χ2=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 Sr0.9Ln0.1CoO3−δ, Ln=Y, Eu, Dy, Ho revealed the presence of crystallites with brownmillerite (a≈2×aper, b≈4×aper, c≈2×aper), tetragonal perovskite (a≈aper, c≈2×aper) and Sr0.7Ln0.3CoO2.62 type (a≈2×aper, c≈4×aper) structures. For Ln=Sm, only XRD cubic perovskite phases were observed for all compositions, 0.1⩽x⩽0.5. In the Sr0.5Eu0.5CoO3−δ sample, crystallites of perovskite, tetragonal perovskite and Sr0.7Ln0.3CoO2.62 type were observed in the TEM study.