Kinetics of Enthalpy Relaxation at the Glass Transition in Ternary Tellurite Glasses

Abstract

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 Eη and the glass transition temperature Tg 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 Tg 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.