Long-term physical ageing in As-Se glasses with short chalcogen chains

Long-term physical ageing of chalcogenide glasses, which occurs over tens of years, is much less understood than the short-term ageing. With Se-rich underconstrained As30Se70 glass as a model composition (consisting of Se-n chains with n <= 3 on average), a microscopic model is developed for this phenomenon by combining information from differential scanning calorimetry, extended x-ray absorption fine structure, Raman, and Se-77 solid state nuclear magnetic resonance spectroscopies. The accompanying changes in the electronic structure of these glasses are investigated by x-ray photoelectron spectroscopy. The data suggest ageing from cooperative relaxation, presumably involving bond switching or reconfiguration of As-Se-Se-As fragments.