Sub-Tg relaxation in Ge5Se95 and As5Se95 glasses

Abstract

Abstract High-purity Ge 5 Se 95 (glass transition temperature, T g = 75°C) and As 5 Se 95 ( T g = 52°C) bulk glasses were prepared by melting pre-distilled or surface oxide-removed 5 and 6N pure raw materials in a fused silica ampoule. The density, ϱ, shear modulus, G , Poisson's ratio, ν, heat capacity, C p , and stress-optic coefficient, B , at λ = 1.8 μ 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 (∼ 20°C) in darkness. For both glasses, the magnitude of B increased by about 50% in a near-exponential manner over the initial 14-day period and leveled thereafter. Associated with the relaxation of B , there appeared some increased, although no more than one standard deviation from the average, in the density and elastic properties of Ge 5 Se 95 . The elastic properties of As 5 Se 95 appeared relatively constant over the 14-day period. The shape of the C p versus T curves for both the glasses changed in the transition region. The relaxation resulted in an increase in the glass transition temperature (defined by the onset of the endothermic transition), with a concurrent decrease in the fictive temperature (defined 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 effective increased degree of crosslinking with time.