Raman Spectrum of Ultrafine Anatase Powders Derived from Hydrolysis of Alkoxide

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Abstract
Ultrafine, nanometer-sized anatase particles were prepared by the hydrolysis of titanium isopropoxide. Their Raman spectra are discussed in view of the finite size effects. The crystallite size D estimated by the X-ray diffraction peaks (Scherrer method) was found to be correlated with the Raman peak width Γ. The relationship could be expressed in the empirical equation, Γ = Γ0 + kD−α with the scaling exponent α of 1.5. Because the anatase crystal spans a three-dimensional network, the result demonstrates that 2× α is equal to the dimensionality of the sample. In addition, the anatase powders prepared by different hydrolysis schemes regressed into curves with different constant terms γ0 and k. The amount of organic residue was mainly affected by the hydrolysis scheme, and the organic residue caused the formation of defects in the crystalline particle by the following heat treatment. Therefore, it is obvious that the variation in Γ0 and k has a close relation to the defect density of the crystalline particles. The defect densities were estimated by using the correlation between the X-ray diffraction and the Raman data.