Initial stage of physical ageing in network glasses

• Published in: Philosophical magazine (Abingdon, England) Vol. 92; no. 33; pp. 4182 - 4193
• Main Authors: Golovchak, R., Ingram, A., Kozdras, A., Vlcek, M., Roiland, C., Bureau, B., Shpotyuk, O.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 21-11-2012; Taylor & Francis
• Subjects: ageing; chalcogenide glass; Chemical Sciences; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; DSC; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Glass transitions; Glasses (including metallic glasses); Material chemistry; Materials science; NMR; Physics; positron annihilation lifetime; Raman scattering; Specific materials; Specific phase transitions; Differential scanning calorimetry; Temperature dependence; Raman spectra; Fluctuations; Densification; Thermogravimetry; Positron annihilation; Shrinkage; Nuclear resonance scattering; Structure relaxation; Glass transition temperature; Chalcogenide glasses; Glass transition; Supercooled liquids; Raman scattering; Aging; Nuclear magnetic resonance; NMR; ageing; positron annihilation lifetime; DSC; chalcogenide glass
• ISSN: 1478-6435; 1478-6443; 1478-6433
• DOI: 10.1080/14786435.2012.704428

An atomistic view on Johari-Goldstein secondary β-relaxation processes responsible for structural relaxation far below the glass transition temperature (T
g
) in network glasses is developed for the archetypal chalcogenide glass, As
20
Se
80
, using positron annihilation lifetime, differential scanning calorimetry, Raman scattering and nuclear magnetic resonance techniques. Increased density fluctuations are shown to be responsible for the initial stage of physical ageing in these materials at the temperatures below T
g
. They are correlated with changes in thermodynamic parameters of structural relaxation through the glass-to-supercooled liquid transition interval. General shrinkage, occurred during the next stage of physical ageing, is shown to be determined by the ability of system to release these redundant open volumes from the glass bulk through the densification process of glass network.