Raman scattering from binary GexSe1-x glasses under hydrostatic pressure shows onset of a steady increase in the frequency of modes of corner-sharing GeSe4 tetrahedral units when the external pressure P exceeds a threshold value Pc. The threshold pressure Pc(x) decreases with x in the 0.15 < x < 0.20 range, nearly vanishes in the 0.20 < x < 0.25 range, and then increases in the 0.25 < x < 1/3 range. These Pc(x) trends closely track those in the non-reversing enthalpy, DHnr(x), near glass transitions (Tgs), and in particular, both DHnr(x) and Pc(x) vanish in the reversibility window (0.20 < x < 0.25). It is suggested that Pc provides a measure of stress at the Raman active units; and its vanishing in the reversibility window suggests that these units are part of an isostatically rigid backbone. Isostaticity also accounts for the non-aging behavior of glasses observed in the reversibility window.
@article{arxiv.0709.4437,
title = {Pressure Raman effects and internal stress in network glasses},
author = {Fei Wang and S. Mamedov and P. Boolchand and B. Goodman and Meera Chandrasekhar},
journal= {arXiv preprint arXiv:0709.4437},
year = {2009}
}