Sub-Tg Enthalpy Relaxation in Milled and Quenched As2S3 Glasses

We investigate the sub-T _g relaxation in both the mechanically milled and the quenched As ₂S ₃ glasses by a differential scanning calorimeter (DSC). The results show that the sub-T _g enthalpy relaxation pattern of the milled As ₂S ₃ glass is similar to that of the quenched glass, but the fictive temperature (T _f) of the former is higher than that of the latter. By performing sub-T _g annealing, we find that the quenched As ₂S ₃ glass exhibits the Johari-Goldstein (JG) relaxation, whereas the milled glass shows the relaxation behavior with the activation energy of ~32RT _g that deviates from the average value of 24RT _g for the JG relaxation. An endotherm occurs prior to the sub-T _g relaxation peak when the milled glass undergoes sufficient sub-T _g annealing (temperature and time). The occurrence of the endothermic pre-peak and the higher activation energy of the milled glass imply its higher structural heterogeneity compared to the quenched glass. The Raman and X-ray photoelectron spectra indicate the existence of the As ₄S ₄ clusters and -S-S- chains in both the milled and the quenched glasses, confirming their structural heterogeneity.