Abstract
The observation of reversibility windows (RWs) in binary GexS100-x, AsxS100-x and ternary GexAsxS100-2x glass systems permits constructing a global topological phase diagram in the Ge-As-S composition triangle. The RW denotes glass compositions for which the enthalpy of relaxation at T-g vanishes, leading to thermally reversing glass transitions. The phase diagram permits delineating glass compositions that are in the flexible phase (FP), intermediate phase (IP), and the stressed rigid phase (SRP) for all ternary GexAsxS100-2x glass compositions. For the IP compositions examined, a general lowering of the molar volumes, V-m, is observed in relation to those for non-IP compositions, giving rise to a volumetric window. Melt dynamics of IP compositions reveal a fragility index, m < 20, lower than that for non-IP melts for which m > 20 displays a fragility window, underscoring in part the reason for the delayed homogenization of melts in these sulfide glasses. The observations of the three types of window characteristics of IP compositions are feasible only when the homogeneous bulk glasses are synthesized, in which the variance ⟨Delta x⟩ in As and Ge concentrations, x, across batch compositions is less than 0.01%. This is established by Fourier transform-Raman profiling of each batch of composition that is synthesized.