LOW-FREQUENCY DYNAMICS IN SILICA XEROGELS

Brillouin and Raman experiments have been performed in hydrogenated si lica sol-gel and vitreous silica samples made by sol-gel processes (xe rogels) and by the melting powder method. The aim of this work has bee n the study of the low-frequency dynamics of sol-gel systems in compar ison with that of amorphous silica. By thermal treatment of the gel a progressive densification of the system was obtained: at 500 degrees C we obtained densification (temperature well below the usual temperatu res); at higher temperature (approximate to 700-800 degrees C) the por es were eliminated and the dynamics (Brillouin shifts, quasielastic sc attering, and Boson peaks) became equivalent to that of fused silica.