Physical aging effects caused by prolonged natural storage $\left(\sim 22\text{years}\right)$ in binary ${\text{As}}_x{\text{Se}}_{100-x}$ glasses are probed by temperature-modulated differential scanning calorimetry. It is shown that all aged samples with $x<40$ reveal nonzero out-of-phase component of complex heat flow testifying physical aging effect. The first composition, which can be attributed to a so-called self-organized phase characterized by the absence of natural physical aging effect, is the stoichiometric ${\text{As}}_2{\text{Se}}_3$ glass; lack of aging within the so-called reversibility window, $28<x<38$, is not found. High-resolution x-ray photoelectron spectroscopy fails to show any evidence of fourfold-coordinated As atoms, which is consistent with the aging ability of glasses with $x<40$.

The long-term kinetics of physical ageing at ambient temperature is studied in Se-rich As-Se glasses using the conventional differential scanning calorimetry technique. It is analysed through the changes in the structural relaxation parameters occurring during the glass-to-supercooled liquid transition in the heating mode. Along with the time dependences of the glass transition temperature (T(g)) and partial area (A) under the endothermic relaxation peak, the enthalpy losses (ΔH) and calculated fictive temperature (T(F)) are analysed as key parameters, characterizing the kinetics of physical ageing. The latter is shown to have step-wise character, revealing some kinds of subsequent plateaus and steep regions. A phenomenological description of physical ageing in the investigated glasses is proposed on the basis of an alignment-shrinkage mechanism and first-order kinetic equations.

International audienceThermal, optical, X-ray excited and magnetic methods were used to develop a microstructural model of physical ageing in Se-rich glasses. The glass composition As10Se90, possessing a typical cross-linked chain structure, was chosen as a model object for the investigations. The effect of physical ageing in this glass was revealed by differential scanning calorimetry, whereas the corresponding changes in its atomic arrangement were studied by extended X-ray absorption fine structure, Raman and solid-state 77Se nuclear magnetic resonance spectroscopy. Straightening-shrinkage processes are shown to be responsible for the physical ageing in this Se-rich As-Se glass

Methodological possibilities of positron annihilation lifetime (PAL) spectroscopy applied to characterize different types of nanomaterials treated within three-term fitting procedure are critically reconsidered. In contrast to conventional three-term analysis based on admixed positron- and positronium-trapping modes, the process of nanostructurization is considered as substitutional positron-positronium trapping within the same host matrix. Developed formalism allows estimate interfacial void volumes responsible for positron trapping and characteristic bulk positron lifetimes in nanoparticle-affected inhomogeneous media. This algorithm was well justified at the example of thermally induced nanostructurization occurring in 80GeSe2-20Ga2Se3 glass.