Temperature-induced structural change through the glass transition of silicate glass by neutron diffraction

Supercooled silicate liquids exhibit several orders of magnitude increase in viscosity at the glass-transition temperature (Tg) towards the glassy state. Such a drastic dynamical slowdown leads to an abrupt change in the slope of temperature-dependent thermodynamic properties because the measurements reflect the equilibrium-to-nonequilibrium change from liquid to glass. However, an underlying structural change associated with such a transition remains elusive. For instance, understanding the structural origin of the variation in the coefficient of thermal expansion (CTE) of silicate glasses upon vitrification is critical for glass-manufacturing processes and applications. Here, based on temperature-dependent neutron diffraction, we demonstrate that the temperature dependences of both short- A nd medium-range order structural parameters show a pronounced change of slope at Tg for a range of silicate glasses of industrial importance. Interestingly, the short- A nd medium-range order structural parameters are found to be mutually correlated, both below and above Tg. Based on these results, we find that the slope change of the area of the first sharp diffraction peak at Tg is correlated with the extent of the CTE jump at Tg, which offers a structural origin for the discontinuity in the CTE of glasses at Tg. This study can therefore shine light on solving critical industrial problems, such as glass relaxation.