XANES studies on rhenium L absorption edges of Re 2O 7 graphite intercalation compounds and of other rhenium-oxygen compounds

Abstract

The electronic structure as well as the medium-range order of rhenium oxides and Re 2O 7 graphite intercalation compounds (GICs) were investigated by analyzing the XANES (X-ray absorption near edge structure) of the Re L I–III absorption edges. The Re L I,III edges show for all perrhenates strong white lines whose full widths decrease going from the solid to the highly concentrated to the highly diluted solution. Coincidently the area of the white lines increases. The GICs show the same dependence with the exception that their absorption peaks are always lower, which is caused by a charge transfer from graphite to rhenium. A reduced intensity of the strong pre-edge peak at the Re L I edges in comparison to solid perrhenates and perrhenate solutions indicates a slightly distorted tetrahedral symmetry for the GICs. The analysis of a multiple scattering feature at the Re L I edge reveals for the GIC intensities similar to the solutions but several times lower than those of the solid perrhenates. The loss of the three-dimensional long-range order after the intercalation accompanied by a low density of ReO 4 tetrahedra causes this effect.