Viscosity study of the optical tellurite glass: 75TeO2–20ZnO–5Na2O

The steady state viscosity of a tellurite glass with composition 75TeO2–20ZnO–5Na2O has been measured using parallel plate rheometry and found to decrease with shear rate and temperature. The viscosity is constant for lower shear rates but decreases rapidly above a critical rate γ̇c, due to shear thinning. The shear rate dependence of the viscosity is found to be well approximated by the Cross model in the temperature range between 609 and 663 K while the temperature dependencies of both the viscosity and relaxation time are observed to follow an Arrhenius law in this temperature range. The activation energy obtained from the Arrhenius fit is used to determine the fragility of the tellurite glass, which is compared to that of other well-known glasses from the literature.