The possible mechanism of lithium exchange from I.iFeTiO(4) is discussed on the basis of three different in situ structural characterization methods. The in situ X-ray diffraction (XRD) showed that the mechanism of lithium exchange was through a solid solution formation whereby the change in volume during the oxidation was 1.4%. The reversibility in terms of charge recuperation was complete: however, after the first reduction, the change in volume was still 0.4%. In situ Mossbauer spectroscopy experiment showed complete Fe(II) oxidization to Fe(III), while the reduction was not reversible. After the complete first cycle. the number of local environments in the Mossbauer spectra needed for a Successful fit increased by at least two. Several local environments can be explained on the basis of extended X-ray absorption fine structure results. In the as-prepared sample. Fe cations are coordinated to three oxygen atoms at 2.03 angstrom and another three at 2.13 angstrom. With the oxidation of Fe, the splitting of two oxygen atoms gradually increases to 0.18 angstrom, and the octahedra deformation gradually changes from 3 + 3 to 4 + 2. This deformation is not reversible and it can explain changes in the long-range order as observed from in Situ XRD. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3205458] All rights reserved.