In situ EXAFS and XANES measurements of the change in Ti coordination during the calcination of a (TiO2)(0.18) (SiO2)(0.82) aerogel

The calcination of a (TiO2)(0.18)(SiO2)(0.82) aerogel has been followed using in situ high-temperature Ti K-edge 'quick EXAFS' and XANES measurements. The results clearly show that the coordination of Ti in this material changes from a mixture of four- and sixfold to predominantly fourfold as the temperature is increased from ambient to 300 degreesC. The decrease in static disorder, as the environment of Ti converts to predominantly a single site, is such that the overall Debye-Waller factor for the Ti-O shell decreases markedly even as the temperature increases to 700 degreesC. Combined 'quick EXAFS' and XANES measurements are shown to be valuable tools for in situ studies of structural changes associated with thermal treatment of amorphous materials.