Influence of fictive temperature and composition of silica glass on anomalous elastic behaviour.

In order to determine the influence of the thermal history (fictive temperature) and OH content on the elastic properties of silica glass, we have investigated high resolution in situ Brillouin experiments on SiO(2) glass from room temperature to the supercooled liquid at 1773 K across the glass transition. The well known anomalous increase of elastic modulus in the glassy state and in the supercooled liquid regime is observed. No change in the slope of the elastic moduli of silica appears as a characteristic of the glass transition, in contrast to what happens in various other glasses. We show that thermal history has a weak effect on elastic moduli in the glass transition regime for silica glass. The effect of the water content in silica glass is greater than the fictive temperature effect and gives larger changes in the amplitude of the elastic modulus for the same thermal dependence. A singular decrease above 1223 K is also observed in the shear moduli for hydrated samples. Different models explaining the temperature dependence of the elastic properties in relationship with frozen-in density fluctuations or with the structure are discussed.