Johari-Goldstein relaxation in quenched and irradiated chalcogenide glasses

Understanding relaxation processes in glasses is essential for linking their micro-scopic dynamics to macroscopic mechanical behavior. As a liquid is cooled toward the glass-transition tem-perature (Tg), its relaxation dynamics separate into two distinct processes: the structural (α) relaxation,involving large-scale cooperative rearrangements, and the faster Johari-Goldstein (JG) or β relaxation, alocalized motion that persists below Tg. The JG relaxation governs the residual mobility of glasses and playsa central role in phenomena such as plastic flow and crystallization. Here, the JG relaxation is investigated inhigh-enthalpy GeSe3 glasses using fast-scanning calorimetry. High-enthalpy glassy states are reachedthrough two independent routes: rapid thermal quenching from the melt and X-ray irradiation of the solidglass. Both methods increase structural disorder and reveal the JG relaxation as an exothermic signal belowTg in the calorimetric traces, corresponding to the release of stored enthalpy from defect regions. Althoughrapidly quenched and X-ray-irradiated samples can exhibit comparable enthalpy levels, their calorimetrictraces differ in shape, indicating distinct microscopic pathways to high-enthalpy states. Notably, the strengthof the JG relaxation is higher in irradiated glasses than in isenthalpic glasses produced by thermal proced-ures, although this difference is reduced for long-irradiated glasses. These results support the view that thesecondary relaxation originates from defect or loosely connected regions within the glass network. Such re-gions act as elementary plastic units whose number increases on increasing the enthalpy of the glass until thematerial yields. This work establishes X-ray irradiation as a controllable and versatile method, complemen-tary to melt quenching, for tuning structural heterogeneity and thereby tailoring the mechanical and relaxa-tion properties of glasses.