Infrared Studies of Titanium-Containing Vitreous Silica

The reflectivity of samples of Corning's ULE glass (7.5{\%} Ti and 92.5{\%} silica), was measured from 18 cm$^{-1}$ to 30000 cm$^{-1}$. The refractive index and extinction coefficient were then calculated using the Jahoda-Velicky dispersion relation. The resulting infrared absorption spectrum is almost identical to that of vitreous silica with the exception of a new absorption band at 941 cm$^{-1}$. The negligible change in the vitreous silica part of the absorption is taken to imply that, at the concentrations present, titanium has little effect on the SiO$_{2}$ network and the environment of Si$^{4+}$ ions. The phase diagram for TiO$_{2}$-SiO$_{2}$ systems and titanium EXAFS measurements$^{2}$ indicate that titanium is tetrahedrally coordinated by O$^{2-}$ ions in ULE glass, i.e., it substitutes for Si$^{4+}$. On this basis the new 941 cm$^{-1}$ band is attributed to an antisymmetric stretching mode of Ti-O-Si units, corresponding to a perturbation of the prominent Si-O-Si antisymmetric stretching mode$^{3}$ seen at 1076 cm$^{-1}$ in vitreous silica. 2. R. B. Greegor, \textit{et al}. J. Non-Crystalline Solids \textbf{55}, 27 (1983). 3. C. T. Kirk, Phys. Rev. \textbf{38}, 1255 (1988).