X-ray absorption fine structure spectroscopy as a probe of local structure in lithium manganese oxides

The use of K-edge X-ray absorption fine structure (XAFS) spectroscopy to characterize the electronic charge and local structure of manganese atoms in LiMn2O4 is discussed with reference to recent communications. The chemical extraction and reinsertion of lithium in LiMn2O4 take place with oxidation and reduction respectively of Mn between 3+/4+ and 4+ states and produce corresponding shifts in the overall position of the X-ray absorption edge. The near-edge structural (XANES) features which have been used in the past to draw conclusions concerning manganese valence are shown to be uniquely characteristic of the medium-range structure around the Mn site and therefore cannot be assigned to different chemical states of the absorbing atom. (C) 1998 Academic Press.