• Keryvin, Vincent
• Sangleboeuf, Jena-Christophe
• Gadaud, Pascal
• Rouxel, Tanguy
• Gueguen, Y.
• Bernard, Cédric

Abstract

The viscous-flow behavior and temperature dependence of the elastic moduli of chalcogenide glasses from the germanium-selenium system were studied by means of homemade high-temperature indentation setup and resonant-frequency technique (1-10 kHz), respectively, for temperatures between 0.8 and 1.2×Tg. The softening rates, both in the elastic and in the viscous-flow regimes, were correlated to network destructuration or reorganization events in the light of previously reported high-temperature neutron-scattering data. The concomitant change of Poisson's ratio (ν) and the thermodynamic parameters of the thermally activated viscous-flow process were characterized and provide a new basis for the understanding of the sources for the softening in the transition range. The temperature dependence of ν suggests weak changes of the network cross-linking degree at large Ge contents. On the contrary, in the case of a-Se, a steep fragmentation of the structural units is inferred from the ν(T) data, and the flow process is accompanied by a huge entropy change (activation entropy at saddle point). The entropy contribution at Tg (Tg ×dSa) represents more than 50% of the activation enthalpy for flow (dHa) and increases with the selenium content. Hence the free activation energy (dGa) is much smaller than apparent activation energy as derived from viscosity data.

Topics

• impedance spectroscopy
• glass
• glass
• viscosity
• thermogravimetry
• elasticity
• activation
• Germanium
• Poisson's ratio