Local distortion in LaCoO₃and PrCoO₃: extended x-ray absorption fine structure, x-ray diffraction and x-ray absorption near edge structure studies

Abstract

Room temperature Co K-edge extended x-ray absorption fine structure (EXAFS),\nx-ray absorption near edge structure (XANES) including pre-edge and x-ray\ndiffraction (XRD) studies are carried out on LaCoO3 and PrCoO3. The Co-O,\nCo-La/Pr and Co-Co bond lengths are obtained from EXAFS analysis and compared\nwith those obtained from XRD. The EXAFS analysis of data indicates that CoO6\noctahedron is distorted in both LaCoO3 and PrCoO3. Such distortion is expected\nin orthorhombic PrCoO3 but not in rhombohedral LaCoO3. This distortion in CoO6\noctahedron is attributed to Jahn-Teller active Co3+ ion in intermediate spin\nstate in these compounds. Higher shell studies reveal that Debye-Waller (DW)\nfactors of Co-Pr and Co-Co bonds in PrCoO3 are more in comparison to Co-La and\nCo-Co bonds in LaCoO3 indicating that these bonds are structurally more\ndisordered in PrCoO3. The comparison of Co-Co bond lengths and corresponding DW\nfactors indicates that the structural disorder plays an important role in\ndeciding the insulating properties of these compounds. XANES studies have shown\nchanges in the intensities and positions of different near edge features.\n