Pressure Raman effects and internal stress in network glasses

TL;DR

This study investigates how internal stress in GexSe1-x glasses affects Raman modes under pressure, revealing a link between stress, network rigidity, and the reversibility window in glass transitions.

Contribution

It introduces pressure Raman effects as a measure of internal stress and demonstrates their correlation with network rigidity and the reversibility window in chalcogenide glasses.

Findings

Threshold pressure Pc(x) varies with composition and vanishes in the reversibility window.

Pc correlates with non-reversing enthalpy DHnr(x) near glass transitions.

Vanishing Pc indicates an isostatically rigid, stress-free backbone.

Abstract

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.