R Malekfar - Department of Physics, University of Tarbit Modares, P. O. Box ۱۴۱۱۵-۱۷۵, Tehran
M Mozaffari - Department of Physics, Islamic Azad University, North-branch, Tehran,

Titanium dioxide (TiO2) has many polymorphs, among them anatase, rutile and brookite are of naturally grown phase. Both anatase and rutile belong to the same crystal symmetry (tetragonal), brookite is orthorhombic. Nanostructured anatase and rutile TiO2 have invoked considerable interest in photocatalysis, photochemical solar cells,gas sensors and white pigment materials. They are wide bandgap semiconductors, transparent in the visible, with high reflective indecies. Rutile is thermodynamically stable and it can be obtained by thermal annealing of amorphous Titania whichtransforms into anatase at moderate temperature [1-6]. Since many of the physical properties of solids are determined by the lattice vibrations [6], more detailed experimental studies of phonon characteristics and lattice vibrational properties of TiO2 nanocrystals are necessary. The as-prepared sample was investigated by XRD pattern, back-scattering dispersive micro-Raman spectroscopy and SEM image. The temperature dependence of Raman spectra of anatase TiO2 nanocrystals were investigated by using variable temperature Raman scattering in the temperature range of 10-300 K. The result will be helpful to get the better understanding of lattice vibration characters in nanocrystalline TiO2 systems. The study of the TiO2 nanocrystals behavior during mechanical treatment, its stability and conditions for phase transition are the aim of this work.