Very long physical ageing in inorganic polymers exemplified by the GexSe1−x vitreous system

Comment on “Molecular origin of aging of pure Se glass: Growth of inter-chain structural correlations, network compaction, and partial ordering” [J. Chem. Phys. 146, 224506 (2017)]

“…It seems quite reasonable that this scenario would result in broadening of W or even T g bifurcation, as observed in some Se-rich Ge-Se glasses after very long physical aging. 4 Nevertheless, this expectation is evidently in conflict with experimental observations on the narrowing of the T g range in the aged glasses. 2,9 Then, one needs to explain why the properties of the aged glass are determined by the only rigid newly formed Ge-rich network, but not a superposition of both Ge-and Se-rich parts.…”

“…Additional argument comes from the fact, that formation of Se 8 crowns in supercooled liquid regime is thermodynamically favorable and irreversible process. 20,21 If it occurred as a result of aging, then the rejuvenation procedure (heating of the glass just above T g ), which is known to completely erase the effect of physical aging, 3,4,12 would become impossible. Even the structure of vitreous Se itself is a matter of ongoing discussions, pertaining to the controversies in the Se chains/rings ratio.…”

Response to “Comment on ‘Molecular origin of aging of pure Se glass: Growth of inter-chain structural correlations, network compaction, and partial ordering’” [J. Chem. Phys. 148, 157101 (2018)]

“…Although bimodal Tgs have been reported for some Se-rich Ge x Se 100x glasses as a result of long-term aging (>13 yr), 3,4 Dash et al 2 observed unimodal Tgs in all their Ge-Se glasses (both fresh and aged for 18 months). The variation of T g (x) in the 0% < x < 10% range for the Ge-Se binary is quite linear in x.…”

“…But this would not be the case if the rejuvenated sample were to have a stoichiometry variation "x" across the batch displaying more than one T g . We have compared the T g endotherms of the glass samples of Dash et al at x = 4% and 8% with those of Saiter et al 3 Shpotyuk et al 1 questioned why does the width of T g of Se-glass narrows upon aging when the glass decouples into polymeric Se n chains and Se 8 rings and becomes more disordered? When Se 8 rings decouple from the backbone of polymeric Se n chains, these do not contribute to the connectivity of the backbone.…”

PAL signature of physical ageing in chalcogenide glasses

“…So, in the present paper the kinetics of PhA is studied for typical representative of network ChG, the glassy g-As 20 Se 80 , chosen as the model object owing to our previous studies of dark PhA in As-Se system [18]. We have implied PAL spectroscopy to study behaviour of structurally intrinsic free volumes during PhA and differential scanning calorimetry (DSC) to control the degree of PhA effect itself.…”