Influence of thermal aging on density fluctuations in oxide glasses measured by small-angle X-ray scattering

Small-angle X-ray measurements of the density fluctuations as a function of temperature and thermal history are performed in silica and float glass. Structural relaxation in the glass transition range is observed for the samples stabilized at high temperature. The amplitude of the density fluctuations in the glassy state depends on the thermal history for samples of same composition. It increases with fictive temperature for silica as well as for float glass. Our results are compared to previous results in oxide glasses or polymers and discussed in relation with the concept of fragility i.e. the temperature sensitivity of viscosity in the liquid state.