Temperature‐dependent grain growth and phase transformation in mixed anatase‐rutile nanocrystalline TiO 2 films

• Published in: Physica status solidi. A, Applications and materials science Applications and materials science, 2011-07, Vol.208 (7), p.1635-1640
• Main Authors: Gnaser, Hubert, Lösch, Jörg, Orendorz, Adam, Ziegler, Christiane
• Format: Article
• Language: English
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.201026784

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.