Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica

TL;DR

This paper investigates the mechanisms of sound damping in densified silica glass, showing that anharmonic coupling primarily explains damping and dispersion, with experimental Brillouin scattering supporting this model.

Contribution

It provides experimental evidence that anharmonicity dominates sound damping in densified silica, contrasting with relaxational models.

Findings

Densified silica's sound damping aligns with anharmonic coupling models.

Thermal relaxation time and unrelaxed velocity are estimated.

Results support anharmonicity as the main damping mechanism.

Abstract

This series discusses the origin of sound damping and dispersion in glasses. In particular, we address the relative importance of anharmonicity versus thermally activated relaxation. In this first article, Brillouin-scattering measurements of permanently densified silica glass are presented. It is found that in this case the results are compatible with a model in which damping and dispersion are only produced by the anharmonic coupling of the sound waves with thermally excited modes. The thermal relaxation time and the unrelaxed velocity are estimated.