A. Kozdras

Atomistic model of physical ageing in Se-rich As–Se glasses

Thermal, 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.

Step-wise kinetics of natural physical ageing in arsenic selenide glasses.

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.

Positronics of subnanometer atomistic imperfections in solids as a high-informative structure characterization tool.

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.

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 Sen 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 77Se 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.

Physical aging of chalcogenide glasses

Physical aging effects are shown to be typical of chalcogenide glasses with an under- or overconstrained network and to influence their physicochemical properties. The natural physical aging of glasses can be accelerated by gamma irradiation or exposure to light.

Physical ageing of chalcogenide glasses

Abstract: This chapter covers state of the art in physical ageing of chalcogenide glasses. The thermodynamic origin of this phenomenon, experimental possibilities for its investigation, up-to-date results, general phenomenology and observed regularities are critically reviewed. The influence of various external factors, such as elevated temperatures, light exposure, high-energy irradiation, on the physical ageing effect in chalcogenide glasses are considered and analyzed from the constraints theory point of view. Possible mechanisms of structural relaxation caused by these factors are discussed thoroughly.

Kinetics of light-assisted physical ageing in chalcogenide glasses

A fundamental understanding of glass relaxation under ambient temperatures, as well as under the external influences is vital to the glass and polymer science communities. Our results show that kinetics of light-assisted physical aging in Se-based glasses can be well fitted with stretch-exponential Kohlrausch type function, which exponent β and the effective time relaxation constant τ depend on the wavelength of incident photons. The obtained β values for Se-rich glasses group around 3/7 and 1/3 values, predicted by Phillips field-free and field-forced axiomatic diffusion-to-traps models.

Initial stage of physical ageing in network glasses

An atomistic view on Johari–Goldstein secondary β-relaxation processes responsible for structural relaxation far below the glass transition temperature (Tg ) in network glasses is developed for the archetypal chalcogenide glass, As20Se80, using positron annihilation lifetime, differential scanning calorimetry, Raman scattering and nuclear magnetic resonance techniques. Increased density fluctuations are shown to be responsible for the initial stage of physical ageing in these materials at the temperatures below Tg . They are correlated with changes in thermodynamic parameters of structural relaxation through the glass-to-supercooled liquid transition interval. General shrinkage, occurred during the next stage of physical ageing, is shown to be determined by the ability of system to release these redundant open volumes from the glass bulk through the densification process of glass network.

Radiation-induced defect formation in chalcogenide glasses

Abstract The modified model of native and radiation-induced microvoid-type positron traps in vitreous chalcogenide semiconductors is developed to explain compositional features of positron annihilation lifetime measurements in stoichiometric As2S3–GeS2 and non-stoichiometric As2S3–Ge2S3 chalcogenide glasses before and after γ-irradiation.

Are the Temperature Sensors Based on Chalcogenide Glass Possible

Principal possibility of the using of chalcogenide glasses (on the example of Ge18As18Se64) as active media for temperature sensors is considered in this work. Differential scanning calorimetry testing of the investigated glasses shown that 2 years of natural storage does not lead to the drift of their DSC-parameters (glass transition temperature and endothermic peak area). Investigation of the temperature dependence of optical transmission spectra shows the linear character of optical band-gap changes with a temperature. Temperature sensitivity index β for Ge18As18Se64 is estimated to be equal to the ~1.2·10-3 eV/°C.