The structural relaxation kinetics at the glass transition in tellurium oxide (TeO2)-based glasses has been examined from viscosity and heat-capacity measurements to clarify the features of the structural relaxation in fragile oxide glass-forming liquids. A large decoupling between enthalpy relaxation and viscous flow, i.e., a large discrepancy between the activation energies for the enthalpy relaxation (recovery), ΔH, and viscous flow, Eη, has been demonstrated in TeO2-based glasses. The values in xK2O·xMgO·(100 - 2x)TeO2 glasses, for example, are ∼919-1051 kJ/mol for ΔH and ∼ 577-701 kJ/mol for Eη, given the ratio of ΔH/Eη ≈ 1.44-1.59. Some viscosity and heat-capacity data (all data have been reported previously) obtained from similar experiments in Sb2O3-B2O3 glasses belonging to the category of strong glass-forming liquids have been reanalyzed in this paper for comparison; a strong coupling was found to exist between ΔH and Eη, i.e., ΔH/Eη ≈ 0.98-1.18. An origin of decoupling between ΔH and Eη in fragile glass-forming systems such as TeO2-based glasses has been discussed by considering the glass structure model for fragile glasses; strongly bonded correlated (highly constrained) regions are surrounded or connected by weakly bonded noncorrelated (unconstrained) parts.
|Number of pages||7|
|Journal||Journal of the American Ceramic Society|
|Publication status||Published - Jan 2002|
ASJC Scopus subject areas
- Ceramics and Composites
- Materials Chemistry