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Temperature‐dependent grain growth and phase transformation in mixed anatase‐rutile nanocrystalline TiO 2 films
Author(s) -
Gnaser Hubert,
Lösch Jörg,
Orendorz Adam,
Ziegler Christiane
Publication year - 2011
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201026784
Subject(s) - crystallite , anatase , rutile , nanocrystalline material , materials science , annealing (glass) , nucleation , grain size , chemical engineering , analytical chemistry (journal) , mineralogy , crystallography , nanotechnology , metallurgy , chemistry , chromatography , photocatalysis , organic chemistry , engineering , catalysis
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.