SUB-T(G) RELAXATION IN CE5SE95 AND AS5SE95 GLASSES

High-purity Ge5Se95 (glass transition temperature, T-g = 75 degrees C) and As5Se95 (T-g = 52 degrees C) bulk glasses were prepared by meltin g pre-distilled or surface oxide-removed 5 and 6N pure raw materials i n a fused silica ampoule. The density, rho, shear modulus, G, Poisson' s ratio, nu, heat capacity, C-p, and stress-optic coefficient, B, at l ambda = 1.8 mu m were measured periodically over about 7 months after cooling to room temperature. In between the measurements, glasses were stored stress-free at room temperature (similar to 20 degrees C) in d arkness. For both glasses, the magnitude of B increased by about 50% i n a near-exponential manner over the initial 14-day period and leveled thereafter. Associated with the relaxation of B, there appeared some increase, although no more than one standard deviation from the averag e, in the density and elastic properties of Ge5Se95. The elastic prope rties of As5Se95 appeared relatively constant over the 14-day period. The shape of the C-p versus T curves for both the glasses changed in t he transition region. The relaxation resulted in an increase in the gl ass transition temperature (defined by the onset of the endothermic tr ansition), with a concurrent decrease in the fictive temperature (defi ned by the equivalent enthalpy). It is suggested that the Ge(As) atoms are under-coordinated in the initial structure, and that the sub-T-g structural relaxation involves coordination changes of these atoms eff ecting increased degree of crosslinking with time.