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

Abstract

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.

Acoustic dynamics of network-forming glasses at mesoscopic wavelengths

“…Experimental values of Г( v ), obtained in v-GeO 2 with different techniques (US (refs 22,23), BLS (refs 24,25,26), INS (ref. 24) experiments and MD (ref.…”

“…24) experiments and MD (ref. 24) simulations) are compared with the present experimental results in Fig. 1.…”

“…In order to identify the crossover frequency between the low/high-frequency regimes, we first make use of a fitting model, used in the previous literature, combining additively an anharmonic and a disorder scattering contribution2427. As the data below ≈100 GHz cannot be described with a simple Akhiezer-like v 2 behaviour (they show a linear dependence upon approaching the crossover region from below), we used an anharmonic contribution ( Г Th ) allowing for a spatially varying relaxation time τ ( V ) with a half-gaussian distribution of activation parameters V (the so called TARP scheme7, thermally activated relaxation processes, see Supplementary Note 1 for further details).…”

“…Equations 1, 2, 3 was previously applied to estimate v c 24 obtaining a value of ≈60 GHz, that is, one order of magnitude below the boson peak located at v B ~750 GHz (ref. 29).…”

Optical and spectroscopic characterization of permanently densified GeO2glasses

“…The structure and dynamics of vitreous GeO 2 have been investigated widely both with experimental (e.g. Raman [1,2], X-Ray and neutron spectroscopy [3][4][5][6]) and theoretical methods (e.g. classical molecular dynamics simulations [7,8] and ab initio calculation [9,10]).…”