Structural transformations in nanocrystalline anatase TiO2 films upon annealing in air

Nanocrystalline anatase TiO2 films were prepared from colloidal suspensions using particles with a size of 12 nm. Their structure was examined by Raman spectroscopy and X-ray diffraction (XRD). The as-prepared specimens exhibit exclusively features due to the anatase phase of TiO2 (e.g., the Eg, B1g and A1g vibration modes in Raman spectroscopy and the characteristic diffraction peaks in XRD). Isochronal annealing of the films in air at temperatures of up to 1320 K effected clear structural changes, observed both in Raman and XRD: the crystallite size increases from ∼13 nm to ∼90 nm between 720 K and 1170 K, with the crystallites remaining in the anatase phase. A phase transition to the rutile phase of TiO2 occurs in the temperature range 1170–1320 K and the average crystallite size increases to ∼160 nm.