AUTHOR=Yue Yuanzheng 

TITLE=Anomalous Enthalpy Relaxation in Vitreous Silica

JOURNAL=Frontiers in Materials

VOLUME=2

YEAR=2015

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2015.00054

DOI=10.3389/fmats.2015.00054

ISSN=2296-8016

ABSTRACT=<p>It is a challenge to calorimetrically determine the glass transition temperature (<italic>T</italic><sub>g</sub>) of vitreous silica. Here, we demonstrate that this challenge mainly arises from the extremely high sensitivity of the <italic>T</italic><sub>g</sub> to the hydroxyl content, but also from decrease of the <italic>T</italic><sub>g</sub> with repeating the calorimetric scans. It is known that the liquid fragility (i.e., the speed of the viscous slow-down of a supercooled liquid at its <italic>T</italic><sub>g</sub> during cooling) has impact on enthalpy relaxation in glass. Here, we find that vitreous silica (as a strong system) exhibits striking anomalies in both glass transition and enthalpy relaxation compared to fragile oxide systems. The anomalous enthalpy relaxation of vitreous silica is discovered by performing the hyperquenching-annealing-calorimetry experiments. We argue that the strong systems like vitreous silica and vitreous Germania relax in a structurally cooperative manner, whereas the fragile ones do in a structurally independent fashion. We discuss the origin of the anomalous enthalpy relaxation in the HQ vitreous silica.</p>