Fragility and molar volumes of non-stoichiometric chalcogenides: The crucial role of melt/glass homogenization

Melt-fragility index (m) and glass molar volumes (Vm) of binary Ge–Se melts/glasses are found to change reproducibly as they are homogenized. Variance of Vm decreases as glasses homogenize, and the mean value of Vm increases to saturate at values characteristic of homogeneous glasses. Variance in fragility index of melts also decreases as they are homogenized, and the mean value of m decreases to acquire values characteristic of homogeneous melts. Broad consequences of these observations on physical behavior of chalcogenides melts/glasses are commented upon. The intrinsically slow kinetics of melt homogenization derives from high viscosity of select super-strong melt compositions in the intermediate phase that serve to bottleneck atomic diffusion at high temperatures.

Schematic of a near homogeneous GexSe100″x melt composed of homogeneous (dark) regions separated by heterogeneous (light) interfacial ones