Sub-Tg enthalpy relaxation in milled and quenched As2S3 glasses

We investigate the sub-Tg relaxation in both the mechanically milled and the quenched As2S3 glasses by a differential scanning calorimeter (DSC). The results show that the sub-Tg enthalpy relaxation pattern of the milled As2S3 glass is similar to that of the quenched glass, but the fictive temperature (Tf) of the former is higher than that of the latter. By performing sub-Tg annealing, we find that the quenched As2S3 glass exhibits the Johari-Goldstein (JG) relaxation, whereas the milled glass shows the relaxation behavior with the activation energy of ~32RTg that deviates from the average value of 24RTg for the JG relaxation. An endotherm occurs prior to the sub-Tg relaxation peak when the milled glass undergoes sufficient sub-Tg 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 As4S4 clusters and -S-S- chains in both the milled and the quenched glasses, confirming their structural heterogeneity.