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 as 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. Rath, C., Mohanty, P., Pandey, A.C., Mishra, N.C.: Journal of Physics D, 2009, 42[20], 205101