Fragility in mixed alkali tellurites

Abstract Linear viscoelastic stress relaxation and calorimetric measurements were performed on a series of mixed alkali tellurite glasses of composition 0.3([xNa2O+(1−x)Li2O])+0.7TeO2 at temperatures near and above the glass transition temperature, Tg. The stress relaxation data were well described by the stretched exponential function, G(t)=G0exp[−(t/τ)β], where τ is the relaxation time, β is the distribution of relaxation times and G0 is the high frequency modulus. The fragility, determined from the temperature dependence of τ, exhibited a minimum in the middle of the mixed alkali composition. A possible connection between the kinetic and the thermodynamic dimensions of this system was established, wherein the heat capacity change at the Tg, ΔCp(Tg), and the fragility are correlated.