Raman spectroscopy of nanophase TiO₂

Raman spectra are reported for consolidated nanophase TiO₂ particles in their as-compacted state and after annealing at a variety of temperatures up to 1273 K. The Raman-active bands normally observed for the rutile form of TiO₂ were present in as-compacted samples having average grain sizes in the range from about 10 to 100 nm. However, significant broadening of these bands was found, which was uncorrelated with initial grain size, but not necessarily with other synthesis-related factors. This broadening decreased upon isochronal annealing at elevated temperatures in air. Based upon these observations, it is concluded that nanophase TiO₂ in the as-consolidated state contains significant defect concentrations within the rutile grains and that these intragrain defects and the grain-boundary regions as well have local atomic structures with the rutile symmetry, albeit with some short-range displacements. Some sporadic sample regions containing small amounts (<5%) of the anatase form of TiO₂ were also found; these traces of anatase transformed to rutile upon annealing in air at temperatures above 883 K.