XAFS STUDY OF CHARGE-TRANSFER IN INTERCALATION COMPOUNDS

An intercalation process is a reversible topotactic reaction in which a guest species occupies empty sites in a solid structure. A charge tr ansfer is always observed between the guest and the host. An accurate knowledge of this electronic exchange, i.e. how many electrons are tra nsferred and on which electronic level, can only be obtained from prec ise electronic band structure calculations. Such calculations have to be supported by experimental data. For this purpose we have compared X -ray absorption spectroscopy (XAS) data with edge simulations in the m ultiple scattering formalism and band structure calculations in using the Tight Binding Linear Muffin Tin Orbitals method in the Atomic Sphe res Approximation (TB-LMTO-ASA) method. This approach is first illustr ated by a study of sulfur K edge on the two modifications (1T and 2H) of tantalum disulfide TaS2. It is then applied for an accurate charact erization of the charge transfer in the case of lithium intercalation into TiS2, from XAFS experiments at the sulfur K edge. It is concluded that sulfur atoms are largely taking part in the intercalation proces s. (C) 1997 Elsevier Science B.V.