Raman spectra of gel-prepared titania-silica glasses

Ultralow expansion TiO₂SiO₂ glasses can be prepared by a variety of sol-gel routes. The Raman spectra are similar to the spectra of glasses prepared by high-temperature melt and vapor deposition techniques. The Raman spectra resemble the spectra of silica glass with the addition of a polarized band at 1106 cm^-1and a depolarized band at 933 cm^-1which varied in intensity with titanium concentration. The spectra are explained in terms of titanium-rich clusters within a matrix of silica-rich glass. The onset of crystallization in heat-treated glasses is seen in the Raman spectra as a series of sharp bands characteristic of the anatase form of TiO₂.