Abstract
Nanocrystalline TiO~2~ films were prepared from colloidal suspensions using a mixture of anatase and rutile TiO~2~ particles. Their structure was examined by X‐ray diffraction (XRD). The as‐prepared specimens exhibit the presence of both anatase and rutile crystallites with average sizes of ∼30 and ∼50 nm, respectively, as determined from their characteristic diffraction peaks in XRD. Isochronal annealing of the films for 90 min in air at temperatures of up to 1270 K effected clear structural changes: between 470 and 870 K, the crystallite sizes do not change, with the crystallites remaining in their original phase. For annealing temperatures T~a~ ≥ 970 K the anatase and rutile grain sizes increase, while above ∼1170 K, the anatase phase disappears and only crystallites in the rutile phase of TiO~2~ are observed. Their size increases further with increasing annealing temperature and reaches ∼150 nm at 1270 K. Concurrently, the weight fraction of rutile changes from an initial value of ∼0.09 (for 470−870 K) to unity (above 1170 K). At T~a~ = 970 K, the increase of the duration of annealing from 90 to 360 min leads to a moderate increase of the crystallite size. The results indicate that the transformation of anatase particles is governed by the concurrent occurrence of interface and surface nucleation processes.