Fracton vibrations in vitreous SiO2 as revealed from Raman spectroscopy study

Low-frequency Raman spectroscopy is used to study the sensitivity of the dy namic (vibrational) properties of the fractal structure of nanocracks in vi treous SiO2 to the mechanical and thermal previous history of the sample. T he material is obtained by vacuum-compression fritting of the sol-gel synth esis products. After fritting, continuity defects having a nanostructural s cale and possessing fractal geometry are left at the site of microcracks in the course of preliminary mechanical processing of the sample. The feature s of such defects are an absence of the boson peak in the Raman spectrum an d a monotonic decrease of the intensity according to the law of light scatt ering from acoustic vibrations of fractals. The conditions for the emergenc e of the fractal structure and its dependence on the rigidity of the walls of nanocracks are determined from the scattering mode. (C) 2001 MAIK "Nauka / Interperiodica".