STRUCTURAL MODELS OF LONG- AND SHORT-TERM PHYSICAL AGEING IN SELENIUM-RICH GLASSES

Long-term and short-term physical ageing effects are studied in a Sebased chalcogenide glasses. The As-Se glasses having long Sen chains (n ≥ 3) in their structure as well as the glasses which network approaches a selforganized phase (optimally constrained network) are examined at the example of As10Se90 and As30Se70 compositions. Physical ageing processes are studied by combining the results of differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine-structure spectroscopy (EXAFS), solid state Se nuclear magnetic resonance (NMR) and Raman spectroscopy. Atomistic model of physical ageing is constructed using these data. Straightening-shrinkage processes of Se chain fragments are considered as the main microstructural mechanism of short-term physical ageing in Se-rich network glasses, while long-term physical ageing in underconstrained glasses with short chalcogen chains (1 ≤ n < 3) is attributed to cooperative many-body relaxation dynamics, slowed down by the rigidity of short polymeric Se-chains below glass transition temperature.

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