The structural relaxation kinetics at the glass transition in tellurium oxide (TeO 2)-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, E η, has been demonstrated in TeO 2-based glasses. The values in xK 2O·xMgO·(100 - 2x)TeO 2 glasses, for example, are ∼919-1051 kJ/mol for ΔH and ∼ 577-701 kJ/mol for E η, 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 Sb 2O 3-B 2O 3 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 E η, i.e., ΔH/E η ≈ 0.98-1.18. An origin of decoupling between ΔH and E η in fragile glass-forming systems such as TeO 2-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