Atomic-scale understanding of structural relaxation in simple and complex borosilicate glasses

The temporal evolution of the coordination environments of B atoms in simple and complex borosilicate glasses following temperature jumps near the glass-transition temperature has been studied using $^{11}\mathrm{B}$ magic-angle-spinning NMR spectroscopy. The relaxation kinetics for boron speciation is found to be in excellent agreement with those for density and shear relaxation at the same temperature, irrespective of the compositional makeup of the glass. Moreover, the temperature dependence of boron speciation is found to be the most important source for the production of configurational entropy in these glasses near the glass-transition range, signifying a direct link between structure, configurational entropy, and viscous flow. When taken together, these results are shown to be consistent with the predictions of the fluctuation-dissipation theorem.