X-ray Absorption near Edge Structure and Crystallographic Studies of the Mixed Valence Oxides CaRu1-xMnxO3

Eleven members of the series CaRu1-xMnxO3 With 0 <= x <= 1 have been prepared and characterized using a combination of Mn K-edge and Ru L-3,L-2-edge X-ray absorption near edge Structure spectroscopy and high resolution synchrotron X-ray powder diffraction. A complex distribution of four Mn3+/4+ and Ru4+/5+ oxidation states was observed and quantified. When incorporated into CaRuO3 at low doping levels, the Mn is present as Mn3+ and Mn4+ with the nominal Mn oxidation state increasing with x (from 3.6 at x = 0.1 to 4 at x = 1). The Ru exists predominantly as Ru5+ in CaMnO3 with the nominal Ru valency as 4.8 at x = 0.9. The formation of Mn3+/4+-Ru4+/5+ redox pairs accounts for the unusual chemical composition dependence of the cell volume, evident from the diffraction studies. The coexistence of mixed valence redox pairs is also believed to contribute to the phase separation observed at 0.1 <= x <= 0.6.