Study of the electronic structural variation of transition metal oxides by X-ray absorption spectroscopy

A number of Os-containing perovskites, Sr2LiOsO6, Sr2CaOsO6, Sr2ScOsO6, and SrLaScOsO6, were synthesized as model compounds. According to powder XRD, both Sr2LiOsO6 and Sr2CaOsO6 have an ordered cubic structure, whereas Sr2ScOsO6 is found to be cubic with partially disordered B site cations (Sc and Os), and SrLaScOsO6 has a completely disordered arrangement. In addition, Sr2CaOsO6 exhibits a larger unit cell parameter than Sr2ScOsO6 due to the larger ionic size of calcium, even though it was expected that the higher oxidation state of Os6+ would contract the crystal lattice. XANES spectra at the Os L-III-edge show two peaks corresponding to the transitions to t(2g) and e(g) states for all compounds, implying the local symmetry around Os ions to be regular octahedral. The peak positions and intensities of the transitions to both states indicate that the Os ions are stabilized in the form of Os7+, Os6+, Os5+, and Os4+ in the octahedral site of the perovskites Sr2LiOsO6, Sr2CaOsO6, Sr2ScOsO6, and SrLaScOsO6, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.