Shift in elastic phase boundaries due to nanoscale phase separation in network glasses: the case of Ge x As x S1 − 2 x

Abstract

Binary and ternary sulphide glasses, in contrast to their selenium counterparts, are usually not fully polymerized. This circumstance provides a means to examine the role of nanoscale phase separation effects on global elastic phase diagrams of disordered networks. In bulk Ge x As x S1 − 2 x glasses, the non-reversing enthalpy (ΔH nr) near T g is found to display a global minimum (∼0) in the 0.11<x<0.15 range, the reversibility window. Furthermore, the ΔH nr term is found to age for glass compositions below (x<0.11) and above (x>0.15) the window, but not in the window. In analogy to corresponding selenides, glass compositions in the window represent the intermediate phase, those at x<0.11 are floppy, and those at x>0.15 stressed-rigid. Raman scattering shows floppy and stressed-rigid networks to consist of S8, and As4S4 and As4S3 monomers, respectively, aspects of structure that contribute to a narrowing of the intermediate phase and to suppression of the ΔH nr term in S-rich glasses qualitatively in relation to corresponding Se-rich glasses that are fully polymerized.