  Phase transition from anatase to rutile for the 70nm TiO2 crystallite has
been investigated by annealing at different temperatures followed by TDPAC
measurement of these TiO2 crystallites adsorbed with 181Hf tracer. The width of
the peaks in XRD spectra for TiO2 crystallites annealed at different
temperatures indicates the growth of the crystallites with temperature. The
samples annealed upto 823K for 4hrs showed no phase transition, except the
growth of the crystallites. However, it showed phase transition at the same
temperature (823K), when annealed for longer duration. Annealing for shorter
duration at 1123K showed phase transition. 181Hf tracer adsorbed on 70 nm
anatase TiO2 is found to be in different polymorphs (anatase & rutile) formed
during annealing process. Surface to bulk mass-transfer is found to play a
significant role in the phase transition process.
