Nanosized TiO2 powders prepared by the sol–gel technique at a precipitation pH of

4.5 or 6.5 consisted of anatase after calcining at 500C. An anatase-to-rutile phase

transformation then occurred at 650C in the case of pH of 6.5 while the

temperature was 850C for the lower-pH sample. The pH effect upon the

precipitation-dependent anatase-to-rutile phase transformation temperature did not

appear to have been reported previously. It was known that the smaller the particle

size, the lower was the anatase-to-rutile phase transformation temperature, and vice

versa. The observation of a larger crystallite size and a lower anatase-to-rutile

phase transformation temperature in the case of the higher-pH sample contradicted

the reported result. It was realized, from X-ray photo-electron spectroscopic

studies, that the oxygen vacancy concentration drove the anatase-to-rutile phase

transformation temperature to lower values in the higher-pH sample as compared

with samples synthesized at a lower pH. Even the particle size was found to be

higher in the former.

Oxygen Vacancy Induced Structural Phase Transformation in TiO2 Nanoparticles.

C.Rath, P.Mohanty, A.C.Pandey, N.C.Mishra: Journal of Physics D, 2009, 42[20],

205101