Slow kinetics of melt homogenization and strong nature of intermediate phase melts in chalcogenides

The strong-fragile classification of melts is manifested in the T-dependence of viscosity. Strong (fragile) melts possess a T-independent (dependent) activation energy of viscosity leading to an Arrhenian (non-Arrhenian) behavior reflecting the robust (weak) nature of network structure. We have now measured [1] complex C$_p$ of binary Ge$_x$Se$_{100-x}$ glasses as a function of x, and find that in dry and homogeneous melts, fragility (m(x)) shows a global minimum (m \textless\ 20) in the Intermediate Phase (IP) compositions (19.5{\%} \textless\ x \textless\ 26{\%}) but increases rapidly outside the IP. These findings have a direct bearing on synthesis of non-stoichiometric melt compositions at elevated temperatures in which IP melt compositions serve as a bottleneck [1] to homogenize [2] batches globally. The physical properties of dry and homogeneous glasses differ significantly from their inhomogeneous counterparts, and have led, in general, to differences in results reported by various groups.\\[4pt] [1] K. Gunasekera et al, ``Fragility and kinetics of melt homogenization of network glasses''(In preparation).\\[0pt] [2] S. Bhosle et al., Solid. St. Comm. 151, 1851-1855 (2011).