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

Abstract

A number of Os-containing perovskites, Sr 2LiOsO 6, Sr 2CaOsO 6, Sr 2ScOsO 6, and SrLaScOsO 6, were synthesized as model compounds. According to powder XRD, both Sr 2LiOsO 6 and Sr 2CaOsO 6 have an ordered cubic structure, whereas Sr 2ScOsO 6 is found to be cubic with partially disordered B site cations (Sc and Os), and SrLaScOsO 6 has a completely disordered arrangement. In addition, Sr 2CaOsO 6 exhibits a larger unit cell parameter than Sr 2ScOsO 6 due to the larger ionic size of calcium, even though it was expected that the higher oxidation state of Os 6+ 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 Os 7+, Os 6+, Os 5+, and Os 4+ in the octahedral site of the perovskites Sr 2LiOsO 6, Sr 2CaOsO 6, Sr 2ScOsO 6, and SrLaScOsO 6, respectively.