Structural characterization, magnetic behavior and high-resolution EELS study of new perovskites Sr2Ru2-xCoxO6-δ (0. 5 ≤ x ≤ 1. 5)

New oxides of general formula Sr2Ru2-xCoxO6-delta (0.5 <= x <= 1.5) have been synthesized as polycrystalline materials and characterized structurally by X-ray diffraction. For 0.5 <= x <= 0.67 the orthorhombic, Pnma, perovskite structure of the end member, SrRuO3, is found. At x = 0.67 a phase separation into an Ru-rich Pnma phase and a Co-rich I2/c phase occurs. The I2/c form is also found for x = 1.0 but another orthorhombic phase, Imma, obtains for x = 1.33 and 1.5. Reductive weight losses indicate negligible oxygen non-stoichiometry, i.e., (delta similar to 0, for all compositions even those rich in Co. High-resolution electron energy loss spectroscopy (EELS) indicates that cobalt is high-spin Co3+ or high-spin Co4+ for all x. Appropriate combinations of Ru4+, Ru5+, HS Co3+ and HS Co4+ are proposed for each x which are consistent with the observed Ru(Co)-O distances. Significant amounts of Co (4+) must be present for large x values to explain the short observed distances. Broad maxima in the d.c. susceptibilities are found between 78 and 97 K with increasing x, along with zero-field-cooled (ZFC) and field-cooled (FC) divergences suggesting glassy magnetic freezing. A feature near 155 K for all samples indicates a residual amount of ferromagnetic SrRuO3 not detected by X-ray diffraction. (C) 2007 Elsevier Inc. All rights reserved.