A PHENOMENOLOGICAL MODEL FOR THE ENTHALPY RELAXATION OF GLASSES .1. SINGLE RELAXATION-TIME APPROACH FOR NONCRYSTALLINE SELENIUM

Relaxation phenomena have become a major concern in non-crystalline materials. In the present paper we deal with a phenomenological model, based on the Kovacs equation, describing enthalpic relaxation in glasses. Only a single relaxation time, tau, is considered. The model is built up in steps of progressive complexity. Here, two cases are distinguished: (i) a pure thermal dependence for tau, and (ii) a combined dependence with temperature and the departure from equilibrium. Comparisons with calorimetric measurements performed on amorphous selenium show generally good agreement, but indicate the need for consideration of a distribution of relaxation times.