Universal behavior of internal friction in glasses below Tg:: Anharmonicity versus relaxation

Comparison of the internal friction Q(-1) at hypersonic frequencies between a few K and the glass transition temperature T-g for various glasses brings out general features. At low temperature, Q(-1) is only weakly dependent on the material. At high temperature but still below T-g the internal friction for strong glasses shows a T-independent plateau in a very wide domain of temperature; in contrast, for fragile glass, a nearly linear variation of Q(-1) with T is observed. Anharmonicity appears dominant over thermally activated relaxational processes at high temperature.