Elastic properties and activation energy profiles of viscosity in Ge–Se system across the glass-transition range

• The relation between the shear modulus and the viscosity of Ge–Se system is examined.
• The Wachtman equation describes reasonably well the shear modulus data.
• The shoving model for viscosity is well applicable even to the glass state.
• The VFT–BSCNF relation is applied to the low viscosity regime.
• The activation energy exhibits a maximum value across the glass-transition range.

The relation between the temperature dependence of shear modulus G(T) and viscosity η(T) of GexSe1 − x (0 ≤x≤0.30) system across the glass-transition range is investigated using several ideas: the Wachtman equation for G, the shoving model and the bond strength–coordination number fluctuation (BSCNF) model of viscosity. Firstly, the present study shows that the empirical Wachtman equation reproduces reasonably well the shear modulus data. Next, it is shown that the shoving model implemented with the analysis of G describes quite well the high viscosity data in the glass state. Besides, the viscosity in the supercooled liquid side, especially for Ge3Se7, exhibits a clear change from Arrhenius-like to VFT-like temperature dependence upon heating. From the viscosity analysis for the composition GeSe4, GeSe3 and Ge3Se7, we obtain a maximum value for the activation energy across the glass-transition range. This result implies that there is an energetic barrier that the structural units need to surmount collectively before the occurrence of the viscous flow. The temperature variation of the activation energy also suggests that in terms of the BSCNF model, the decomposition of network structure upon heating is linked with the collective excitations of the structural units, which gives a viewpoint relevant to the softening of glass.