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Accueil > La Recherche > Axes & Equipes > Matière Molle & Verres > Equipe : Physique des Verres > Thème : Structure, vibration, relaxations dans les systèmes désordonnés
Anharmonic vs. relaxational sound damping in silica glasses
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Involved researchers : M. Foret, R. Vacher, E. Courtens
The temperature dependence of the frequency dispersion in the sound velocity and damping of vitreous silica is reanalyzed. Thermally activated relaxation accounts for the sound attenuation observed above 10 K at sonic and ultrasonic frequencies. Its extrapolation to the hypersonic regime reveals that the anharmonic coupling to the thermal bath becomes important in Brillouin-scattering measurements. At 35 GHz and room temperature, the damping due to this anharmonicity is found to be nearly twice that produced by thermally activated relaxation. The analysis also reveals a sizeable velocity increase with temperature which is not related with sound dispersion. A possible explanation is that silica experiences a gradual structural change that already starts well below room temperature. In the case of permanently densified silica glass, it is found that 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.
E. Courtens, M. Foret, B. Rufflé, and R. Vacher, Elasticity and anelasticity of oxide glasses, Eur. J. Glass Sci. and Technol. B 48 9 (2007).
R. Vacher, E. Courtens, M. Foret, Anharmonic versus relaxational sound damping in glasses. II. Vitreous silica, Phys. Rev. B, 72, 214205 (2005)
E. Rat, M. Foret, G. Massiera, R. Vialla, M. Arai, R. Vacher, E. Courtens, Anharmonic versus relaxational sound damping in glasses. I. Brillouin scattering from densified silica, Phys. Rev. B, 72, 214204 (2005)
