Shift in elastic phase boundaries due to nanoscale phase separation in network glasses: the case of Ge_xAs_xS_1 − 2x

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 S_{1 −  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.

Acknowledgements

We have benefited from discussions with D. McDaniel, B. Goodman and Ping Chen during the course of this work. This work is supported by NSF grant DMR-01-01808.