Melt Dynamics, Nature Of Glass Transition And Topological Phases Of Equimolar Gexasxs100-2x Ternary Glasses

The Topological Phases (TPs) in specially homogenized equimolar GexAsxS100-2x ternary glasses are established here by performing detailed Raman scattering, together with Modulated-DSC and Volumetric measurements over a wide range of compositions, 5% < x < 25%. Our results show the presence of an Intermediate Phase (IP) residing in the 9.0% < x < 16.0% range, with compositions x < 9.0% in the flexible phase, and compositions x > 16% in the stressed-rigid phase. The novel use of ex-situ Raman profiling on the entire batch of compositions indicates very slow dynamics that is tracked with time and composition and reveals the impact of homogenization on physico-chemical properties of glasses. Stressed-Rigid glasses exceeding the chemical threshold composition are all found to be nanoscale phase separated. In the presently synthesized specially homogenized melts/glasses, we observe (i) evidence for the elusive 537 cm(-1) Raman active mode of the S = As stretch in quasi-tetrahedral S = As(S-1/2)(3) local structure, (ii) a square-well like variation of the non-reversing enthalpy of relaxation Delta H-nr(x) at T-g displaying the Reversibility window and defining the Intermediate Phase (IP), (ii) a square-well like variation of molar volumes, V-m(x) coinciding with the IP composition range defining a Volumetric window, (iii) Melt fragility index, m(x), variation showing a global minimum in the IP compositions with m(x) < 20, and with the fragility index, m(x) > 20 for non-IP compositions, defining a Fragility Anomaly, and finally a variation in the specific heat jump near Tg, Delta(Cp)(x), that tracks part of the observed anomalies in m(x) and Delta H-nr(x). The location of each of these anomalies/windows coinciding with those of the IP highlights the privileged nature of the window edge compositions that represent respectively rigidity- (x(r) = 9.0%)- and the stress- (x(s) = 16.0%) elastic phase transitions determined within the Topological Constraint Theory of glasses. (C) 2021 Elsevier B.V. All rights reserved.