Solid State Sciences 6 (2004) 539–546 www.elsevier.com/locate/ssscie Synthesis and characterization of Sr 1−x Ln x CoO 3−δ , Ln = Y, Sm–Tm, 0.1  x  0.5 S.Ya. Istomin a,∗ , O.A. Drozhzhin b , G. Svensson c , E.V. Antipov a a Department of Chemistry, Moscow State University, 119899 Moscow, Russia b Department of Materials Science, 119899 Moscow, Russia c Department of Structural Chemistry, Stockholm University, 10691 Stockholm, Sweden Received 24 November 2003; accepted 22 March 2004 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 0.7 Ho 0.3 CoO 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 0.7 Y 0.3 CoO 2.62 , a ≈ 2 × a per , c ≈ 4 × a per (a per perovskite subcell) was observed. The crystal and magnetic structures of Sr 0.7 Dy 0.3 CoO 2.62 were refined using neutron diffraction data (I 4/mmm, a = 7.6280(8), c = 15.338(2) Å, R p = 0.0332, R 2 F = 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 0.1 CoO 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 0.3 CoO 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 0.5 Eu 0.5 CoO 3−δ sample, crystallites of perovskite, tetragonal perovskite and Sr 0.7 Ln 0.3 CoO 2.62 type were observed in the TEM study.  2004 Elsevier SAS. All rights reserved. Keywords: Perovskites; Complex cobalt oxides; X-ray diffraction; Electron microscopy 1. Introduction Complex cobalt oxides with perovskite-like structures, Sr 1−x Ln x CoO 3−δ (Ln = rare-earth cation), are attracting at- tention as promising materials for use in high-temperature electrochemical devices such as solid-oxide fuel cells (SOFC) and dense membranes to separate oxygen from gas mixtures. To understand the properties of these compounds, precise structural information is needed. A majority of struc- tural studies of compounds in the Sr 1−x Ln x CoO 3−δ sys- tem concern Sr 1−x La x CoO 3−δ [1–3]. However, even for these compounds little crystal structural information is avail- able for low lanthanum contents, x = 0.1–0.3 [1–3], where among others both cubic and brownmillerite type phases have been reported. The latter is not surprising, because un- * Corresponding author. E-mail address: istomin@icr.chem.msu.ru (S.Ya. Istomin). doped brownmillerite-type Sr 2 Co 2 O 5 is known to be sta- ble at high temperatures in the SrCoO 3−x system [4,5]. In the other Sr 1−x Ln x CoO 3−δ systems, mainly Ln = Pr, Gd, Sm and Eu have been studied [6–10]. Depending on composition, a number of different distorted perovskite- related phases have been reported in these systems: tetrag- onal (a = a per , c = a per , Ln = Gd [7]; a ≈ 2 × √ 2 × a per , c ≈ 2 × a per , Ln = Sm [9]) and orthorhombic GdFeO 3 - type (a ≈ √ 2 × a per , b ≈ √ 2 × a per , c ≈ 2 × a per for Ln = Pr, Gd, Sm, Eu [8,7,9,10]). Formation of cubic per- ovskite phases was found for all Sr 1−x Ln x CoO 3−δ , Ln = Pr, Gd, Sm and Eu. The phase formation in these systems is obviously complicated, and the ordering of the oxygen atoms often occurs at a micro level. Therefore the tradi- tional X-ray and neutron diffraction (XRD, NPD) studies on powders have to be complemented with electron diffrac- tion (ED) and high-resolution electron microscope (HREM) techniques. 1293-2558/$ – see front matter  2004 Elsevier SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2004.03.029