Bond-changing structural rearrangement in glassy As3Se7 associated with long-term physical aging

Medium range order and structural relaxation in As–Se network glasses through FSDP analysis

“…In general, the ∆H follows a sigmoidal time dependence, which is defined by a choice of ageing temperature T a in respect to T g (increasing T a accelerates structural relaxation kinetics) [8]. For glasses with low T g , significant enthalpy losses can be observed at room temperature over a short period of time, while for glasses with higher T g , longer periods of storage are needed to observe physical ageing at room temperature [15][16][17]. The investigated arsenic selenide glasses show decrease in the value of physical ageing at room temperature towards the stoichiometric As 2 Se 3 composition [17], which has the highest T g among all As-Se glasses [9,11].…”

“…Different theoretical and experimental methods have been used so far to elucidate structural transformations during physical ageing in ChG. Most popular experimental techniques include Raman spectroscopy, nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS), high-resolution X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS) [14][15][16][17][18]. However, the data from these techniques show insignificant difference between the SRO structural parameters of the aged and non-aged glasses.…”

“…The SRO remains practically invariant during physical aging. Although some minor structural transformations were detected, like 5-7% redistribution of Se atoms between different structural fragments [14][15][16], they could not explain the large changes in T g value and enthalpy losses (∆H) observed with thermal analysis technique after prolong storage [17], as well as plateaus and steep regions in long-term kinetics of enthalpy relaxation [13]. Therefore, significant changes at MRO were anticipated.…”

Network-Forming Nanoclusters in Binary As–S/Se Glasses: From Ab Initio Quantum Chemical Modeling to Experimental Evidences

“…That is why the As 3 Se 7 glass corresponding to Z  = 2.30, which is nominally composed of trigonal AsSe 3/2 pyramids interlinked via double-atoms Ch chains (i.e., =As–Se–Se–As= units), demonstrates an obvious propensity to long-term physical aging due to local decomposition on short =As–Se–As= and long =As–Se–Se–Se–As= chain-like structural fragments, as it was convincingly evidenced from recent Raman scattering, NMR and high-resolution XPS measurements [36, 37]. More generally, the local chemical decomposition by reaction (1) dominates over global phase separation by reaction (2) in binary As–Se ChG, thus meaning shift in the stability onset of this system towards Ch-less compositions ( Z  ≥ 2.29).…”