Among three TiO2 polymorphs, rutile is thermodynamically unstable as compared with anatase and brookite when the crystal size is ∼10 nm. In this study, nanocrystalline rutile with an average grain size of ∼6 nm was synthesized in a thin film geometry by ion beam-assisted deposition (IBAD) with an amorphous TiO2 interlayer between the rutile film and Si-substrate. Nonstoichiometry produced by high-intensity ion bombardment during deposition may have stabilized the metastable rutile phase on the nanoscale. The phase stability of nanosized rutile was investigated by irradiation using 1 MeV Kr2+ combined with thermal annealing. In situ transmission electron microscopy (TEM) results indicate that partial amorphization occurred in nanocrystalline rutile when irradiated at room temperature, whereas the nanocrystals remained stable upon irradiation at 573 K. Ion beam-induced recrystallization occurred in the amorphous TiO2 at a 573 K, significantly lower than the temperature for thermally induced recrystallization, which occurs at 673 K. This is an example of radiation-enhanced kinetics of a phase transformation. With a further increase in the irradiation temperature, to 1073 K, the tetragonal rutile transformed to triclinic Ti5O9.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films