Acoustic damping and dispersion in vitreous germanium oxide

TL;DR

This study investigates sound velocity and attenuation in vitreous germanium oxide across a wide frequency range, revealing the roles of relaxation mechanisms and potential local structural transitions affecting acoustic properties.

Contribution

It provides new Brillouin scattering measurements and integrates them with existing data to analyze damping mechanisms and structural transitions in vitreous germanium oxide.

Findings

Attenuation at sonic and ultrasonic frequencies is explained by thermally activated relaxation.

Network viscosity contributes significantly to damping at hypersonic frequencies.

Bare velocity increases above 250 K, suggesting a local polyamorphic transition.

Abstract

New Brillouin scattering measurements of velocity and attenuation of sound in the hypersonic regime are presented. The data are analyzed together with the literature results at sonic and ultrasonic frequencies. As usual, thermally activated relaxation of structural entities describes the attenuation at sonic and ultrasonic frequencies. As already shown in vitreous silica, we conclude that the damping by network viscosity, resulting from relaxation of thermal phonons, must be taken into account to describe the attenuation at hypersonic frequencies. In addition, the bare velocity obtained by subtracting to the experimental data the effect of the two above mechanisms is constant for temperatures below 250 K, but increases almost linearly above, up to the glass transition temperature. This might indicate the presence of a progressive local polyamorphic transition, as already suggested for vitreous silica.