Relaxation of silica above and below T-g: light scattering studies

In a pure silica glass, different fictive temperatures are achieved between 1500 and 1100degreesC. These temperatures are checked by the position of the Si-O-Si Raman band. Light scattering for the different samples due to density fluctuations is determined by the Landau-Placzek ratio which decreases when T-f decreases. Further relaxation occurs in this glass 300degreesC below T-g; it is interpreted in correlation with the subrelaxational process induced by the diffusion of a few parts per million of impurities.