Dynamic-to-static crossover in the acoustic attenuation of v-GeO ₂

The acoustic attenuation of vitreous germania (v-GeO₂) has been measured over more than three decades in frequency, by means of neutron scattering at high-frequency (THz), visible light scattering and the newly developed technique of Brillouin ultraviolet scattering at lower frequencies (15-50 GHz). The experiments are supported by a molecular dynamics study of a simulated sample of v-GeO₂. The temperature dependence, from 80 K up to the glass transition temperature, shows a persistence of the dynamical nature of the attenuation in the GHz range and a simultaneous increase of the contribution coming from the structural disorder. At higher frequencies clear evidences of a crossover to a region where the attenuation is induced only by the topological disorder are found.