J. Phys. IV France 7 (1997) C2-191-C2-193
Ti K-Edge XANES Studies of Oxides: Theory vs. ExperimentF. Farges1, G.E. Brown Jr.2 and J.J. Rehr3
1 Laboratoire de Physique et Mécanique des Géomatériaux, Université de Marne-la-Vallée (and URA 734 du CNRS, and LURE and Stanford University), 93166 Noisy-le-Grand cedex, France
2 Department of Geological & Environmental Sciences and SSRL, Stanford University, Stanford, CA 94305-2115, U.S.A.
3 Department of Physics, University of Washington, Seattle, WA 98195, U.S.A.
Ti K-edge x-ray absorption near edge structure (XANES) spectra for a variety of Ti(IV)-bearing crystalline oxide model compounds have been measured and compared to ab-initio multiple-scattering XANES calculations using the FEFF6 code. Depending on Ti-coordination (4, 5, or 6), the pre-edge features are found to vary in both position (by ≈ 2 ± 0.1 eV) and normalized height (from ≈ 0.04 to ≈ 1.0), in agreement with the calculations. In compounds where the Ti-coordination is unknown (e.g., glasses and melts), both pre-edge position and height must be used to derive reliable coordination information for Ti. Use of both pre-edge parameters allows one to differentiate, for instance, between 100% of 5-coordinated Ti and a 50:50 mixture of 4- and 6-Ti. Finally, the intensity of the main-edge features can be used as a direct probe of disorder in the short- and medium-range environment of Ti, as exemplified by the comparison of the theoretical and measured XANES spectra obtained for several crystals and their amorphous analogs such as crystalline and radiation-damaged CaTiSiO5 and glassy and molten titanosilicates in the 4.5-1550 K range.
© EDP Sciences 1997