Structural investigation of pristine and annealed nanocrystalline TiO₂ thin films by X‐ray diffraction and Raman spectroscopy

Abstract

Abstract Nanocrystalline anatase TiO 2 films were prepared from colloidal suspensions using particles with a nominal 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 TiO 2 (e.g., the E g , B 1g and A 1g 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 ∼125 nm between 470 K and 1220 K, with the crystallites remaining in the anatase phase. A phase transition to the rutile phase of TiO 2 occurs gradually in the temperature range 1220 – 1320 K and the average crystallite size increases to ∼160 nm. The E g vibration in anatase films reveals a blue shift and an asymmetric peak broadening towards higher frequencies for smaller particle size/lower annealing temperatures. A power‐law dependence between the Raman peak width and the inverse of the crystallite size is found. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)