Structure and dynamics of hydrogenated silica xerogel by Raman and Brillouin scattering

Structure and dynamics of silica xerogel samples are compared with melt quenched amorphous silica by means of infrared, Raman and Brillouin spectroscopes. In particular the attention was concentrated on a family of hydrogenated sol-gel systems whose nominal stoichiometric formula is Si2O3H2, Si8O13H6, Si4O7H2, and Si8O15H2. Thermal treatment of the samples were made at 500 degrees C and at 800 degrees C for 24 h. Samples were cooled at a rate of 0.3 degrees C/min. Densities were measured by pycnometer technique. The densification of the sol-gel network occurs at about 500 degrees C depending on the samples. At about 800 degrees C the structure and the dynamics together with physical properties, such as sound velocities and elastic constants, become indistinguishable from those of glasses derived from melting.