Kinetics of enthalphy relaxation at the glass transition in ternary tellurite glasses

The kinetics of enthalpy relaxation (recovery) at the glass transition in xK₂O·(20 - x)MgO·80TeO₂ glasses has been examined from heat capacity measurements using differential scanning calorimetry to clarify the features of the structural relaxation in ternary TeO₂-based glasses. Ternary glasses such as 10K₂O·10MgO·80TeO₂ show high thermal resistance against crystallization compared with binary glasses. The degree of fragility m estimated from the activation energy for viscous flow E_η and the glass transition temperature T_g is m = 55-62, indicating a fragile character in TeO₂-based glasses. Large heat capacity changes of 43.1-48.2 J·mol^-1·K^-1 are also observed at the glass transition. The activation energy for enthalpy relaxation ΔH is evaluated from the cooling rate dependence of the limiting fictive temperature, and values of ΔH = 897-1268 kJ·mol^-1 are obtained. Negative deviation from additivity in ΔH is also observed. Values of the Kovacs-Aklonis-Huchinson-Ramos (KAHR) parameter θ estimated from ΔH and T_g are 0.33-0.42 K^-1. It has been proposed that ternary glasses have more homogeneous and constrained glass structure compared with binary glasses.