The effect of material aging on crystallization kinetics of Se70Te30 glass

The effect of long-term room-temperature degradation (up to 6 months) on Se70Te30 crystallization kinetics was investigated by differential scanning calorimetry in dependence on experimental conditions of the measurement-applied heating rate and particle size of the powdered material. In case of very fine powders massive amorphous-to-crystalline degradation occurred even at room temperature, indicating that the small powder grains have fully defects-imbued inner structure that accelerates crystal growth. The kinetic data obtained for the consequent crystallization of the remaining glassy matrix showed that the defects-based Johnson-Mehl-Avrami crystallization is under quasi-equilibrium conditions further accelerated towards autocatalytic mechanism. Coarse powders, on the other hand, exhibited primary degradation only in a surface layer of the powder grains. The main effect of the coarse powders aging was found to be associated with marked enhancement of crystal growth originating from volume-located nuclei-either a sub-Tg nucleation occurred during aging or some pre-existing nuclei were activated during this time (possibly via mechanical stresses arising from structural relaxation processes).