Thermal and gamma-ray induced relaxation in As-S glasses: modelling and experiment

Enthalpy relaxation was measured in a series of As-S glasses irradiated with gamma rays and these samples are compared with a set of identical control samples kept in the dark. It is shown that gamma irradiation lifts the kinetic barrier for relaxation at room temperature and speeds up the enthalpy release. The measured values of thermal relaxation in the dark agree closely with modelling results obtained by fitting differential scanning calorimetry curves with the Tool-Narayanaswamy-Moynihan (TNM) equations. The measured values of activation energy for enthalpy relaxation are also in close agreement with that predicted by the TNM model, therefore lending credence to the fitting results. These measurements permit extraction of the effect of gamma irradiation on the glass structure for a series of As-S glasses with increasing structural coordination, and gamma irradiation is shown to reduce the structural relaxation time. It is also shown that lower coordination glasses exhibit greater radiation sensitivity but also greater thermal relaxation due to their lower Tg. On the other end, over-coordinated glasses show lower relaxation and almost no radiation sensitivity. This behaviour is similar to the glass response under sub-bandgap light irradiation.