X-RAY-ABSORPTION SPECTROSCOPIC STUDIES ON LAYERED FEWO4CL AND ITS LITHIUM INTERCALATE

Lithium intercalation into FeWO4Cl leads to the structural phase trans formation from tetragonal to monoclinic. According to Fe K-edge X-ray absorption near edge structure (XANES) spectroscopic analysis, only th e Fe3+ ion in the FeWO4Cl lattice is reduced to Fe2+ with an increment of site symmetry from C-4v to O-h upon lithium intercalation. On the other hand, the white line intensity at the W L-edge XANES becomes sli ghtly enhanced after intercalation, indicating an increase of the (W6-O) bond covalency due to a decrease of the competing (Fe2+-O) bond st rength. W L-3-edge extended X-ray absorption fine structure (EXAFS) an alyses for FeWO4Cl and LiFeWO4Cl show that the regular tetrahedron the WO42- group in FeWO4Cl becomes distorted upon lithium intercalation.