Ti K-Edge XANES Studies of Oxides: Theory vs. Experiment

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