Brillouin scattering measurements of B2O3, GeO2 and SiO2 glasses and liquids, to temperatures ≤ 1550 °C, reveal anomalous thermo-mechanical behavior. Transverse acoustic waves are supported by the liquids of all three oxides. In all systems, the longitudinal and shear elastic moduli increase with increasing temperature below, and again far above the glass transition. This apparent strengthening of the glassy network below Tg is less pronounced, the more fragile the glass former, while in the molten state the opposite seems to be the case. This positive temperature dependence of the elastic properties can be explained by localized structural reorganizations which do not require the breaking of network bonds. The decrease in elastic moduli immediately above Tg, characteristic of fragile systems, is due to the increase of the average network ring size, achieved through a low-activation energy neighbor exchange mechanism. The ability of these liquids to support shear stresses at very high temperatures indicates a persistent network structure.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Materials Chemistry