Elastic moduli of Ge Se (x ≤ 10) glasses in the transition range: implications for elastic models of viscous flow

The elastic moduli of GexSe100−x (0 ≤ x ≤ 10) glasses and deeply supercooled liquids are determined across the glass transition between ambient temperature and 1.16 Tg using resonant ultrasound spectroscopy. The temperature dependence of the high-frequency shear modulus G∞(T) at T > Tg is found to be consistent with the predictions of the elastic models of viscous flow that consider the energy barrier to the structural rearrangement associated with an elementary flow event to be governed by G∞(T). A strong correlation between the fragility indices of these liquids and |∂G∞∂T| at T > Tg indicates a clear connection between their entropic and elastic properties. Finally, the rise in the Poisson's ratio of these liquids with temperature is argued to be a consequence of the composition dependence of ∂G∞∂T, as the temperature derivative of their bulk modulus is an order of magnitude lower than ∂G∞∂T at T > Tg.