Pressure Raman effects and internal stress in network glasses

Abstract

Raman scattering from binary Ge x Se 1−x glasses under hydrostatic pressure shows onset of a steady increase in the frequency of modes of corner-sharing GeSe 4 tetrahedral units when the external pressure P exceeds a threshold value P c . The threshold pressure P c ͑x͒ decreases with x in the 0.15Ͻ x Ͻ 0.20 range, nearly vanishes in the 0.20Ͻ x Ͻ 0.25 range, and then increases in the 0.25Ͻ x Ͻ 1 / 3 range. These P c ͑x͒ trends closely track those in the nonreversing enthalpy, ⌬H nr ͑x͒, near glass transitions ͑T g s͒, and in particular, both ⌬H nr ͑x͒ and P c͑x͒ vanish in the reversibility window ͑0.20Ͻ x Ͻ 0.25͒. It is suggested that P c 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 nonaging behavior of glasses observed in the reversibility window.

Non-volatile Memory Devices Based on Chalcogenide Materials

“…Boolchand et. al. suggested that chalcogenide glasses display three elastic phases as a function of their mean coordination number: floppy phase, Intermediate phase (IP) and stressed rigid phase (Fig 2) [ [10][11][12][13][14][15][16][17][18][19][20][21][22]. Glass compositions in floppy phase and stressed rigid phase are usually poor glass formers due to the high internal stress in their molecular structure.…”

A stringent test for hydrophobicity scales: Two proteins with 88% sequence identity but different structure and function

“…The idea has more than one source: quite early, one of us suggested that some network glasses could be self-organized and that this organization would optimize their ability to fill space with a constrained and compacted (''folded''), yet unstressed (easily deformed), network (3). The relevance of these ideas to proteins became much greater after the discovery of the stressfree reversibility window in the phase diagrams of both chalcogenide and oxide network glasses as well as solid electrolytes (4,5); this discovery solves the otherwise intractable problem of entanglement of exponentially complex, deformed networks, which overhung all such networks (network glasses as much as proteins).…”

“…It also involves compacting the protein in a stress-free way similar to that found in network glasses in the reversibility window (3)(4)(5). Hydro(philic,phobic) residues will have large (small) SASA, which will generally change gradually, if that is allowed by connectivity.…”

“…Methods for treating this technically formidable problem have been developed for network glasses, which are reasonably close in character to proteins (3)(4)(5). In practice, however, some way is still needed to bring in individual amino acid properties in the protein context.…”

Publishing perils include single-blind review

“…The internal networks associated with this novel phase have properties of great technological importance: They are rigid but still free of internal stress. 3 That combination of properties makes it possible to produce window glass on large scales without having it crack or crystallize.…”