Effects of Confinement, Strain and Nonstoichiometry on Raman Spectra of Anatase TiO2 Nanopowders

Nanosized titanium dioxide (TiO2) powders in anatase phase were prepared by laserinduced pyrolysis. Specific surface area of as-grown powders measured by BET method was between 77 and 110 m2/g. The particle sizes (14.4-20.6 nm) estimated from these data coincide well with the crystallite sizes (12.3-17.4 nm) determined by XRD measurements. The mean particle sizes (35-41 nm) obtained from the subsequent SEM measurements refer to considerable agglomeration of nanoparticles. Raman spectroscopy has been used to investigate the structural properties as well as the changes under laser irradiation of TiO2 nanopowders. The blueshift and broadening of the lowest frequency Eg Raman mode were analyzed using a phonon-confinement model which includes strain effect and broadening associated with the size distribution. Influence of the nonstoichiometry and anharmonic effects on this mode have been also investigated. Besides, different changes in Raman spectra after the laser irradiation in vacuum were observed for the nanopowders with different strain values.