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In‐situ Brillouin light scattering (BLS) experiments were carried out to measure both longitudinal and shear sound velocities of air‐cooled and annealed sodium borate glasses xNa2O–(100−x)B2O3 (x = 10, 15, 20, 25, 30, and 35 mol%) from room temperature to temperatures beyond the glass transition temperature (Tg) for each composition. This allows us to access the complete set of elastic moduli at high temperatures and to study the effect of thermal history on physical properties of this system. On heating air‐cooled glasses of lower Na2O content, elastic moduli increase anomalously with increasing temperature just below their Tg, whereas this behavior is absent in corresponding annealed glasses. This anomalous increase in elastic moduli with temperature was not observed in glasses of higher Na2O content. These differences were explained by different structural relaxation mechanisms in the glass transition range in sodium borate glasses of different compositions based on Raman spectroscopy studies in this work and in literature.

For most glass-forming liquids, the temperature dependence of viscosity is non-Arrhenius. Despite the technological and geological importance, the origin of this non-Arrhenius temperature dependence of viscosity remains elusive to date and constitutes an important but unsolved problem in condensed matter physics. It has become increasingly clear in recent years that high-temperature elasticity and viscosity of glass-forming liquids are strongly correlated. This work proposes a modified elastic model to predict equilibrium viscosity of glass-forming liquids. The new elastic model considers the configurational entropy as a factor controlling the activation energy for viscous flow in addition to the high-frequency shear modulus as in the Dyre shoving model. It works much better than the shoving model in fitting equilibrium viscosity for both strong and fragile systems. The new model also has the capability to estimate the nonequilibrium isostructural viscosity of glass from the equilibrium viscosity and the temperaturedependent elasticity of the glassy state.