XAS AND XRD STUDIES ON GRAPHITE-INTERCALATION COMPOUNDS OF RE2O7

Re2O7 was used as starting material for the preparation of pine few-stage graphite intercalation compounds (GICs). X-ray absorption measurements were carried out at the Re L(III) and L(I) absorption edges. The EXAFS analysis resulted in a coordination number of four and a Re-O bond length of 173.5 pm for the GICs. In the Re L(I) XANES the analysis of the strong prepeak confirmed a slight distorted tetrahedral symmetry. Further XANES features indicated a variation of long-range order for the intercalate. Therefore the XAS measurements determined the tetrahedral perrhenate ion as the intercalated species. The majority of synthesized compounds showed sharp hk0 diffraction patterns. Only some compounds showed first diffuse rings and after several days sharp reflections of an ordered ''in-plane'' lattice. The analysis of the hk0 diffraction pattern yielded a lattice with the constants a = 652 pm, b = 764 pm, gamma = 100 degrees, delta(a) = 0.6 degrees and delta(b) = 19.4 degrees.