Positive sound dispersion in vitreous GeO2 at high pressure
Résumé
We determined the density fluctuations spectrum [S(Q,ω)] of vitreous and polycrystalline GeO2 by inelasticx-ray scattering in the wave vector (Q) range between 3 and 13 nm−1 at pressures (P) between ambient and7.1 GPa. The polycrystalline sample displays the expected P evolution of theQ-dispersion relation of longitudinalacoustic (LA) modes. On the contrary, the dispersion relation of the glassy sample for P 1 GPa shows anexcess energy of the LA modes, while at ambient pressure follows the trend expected from ultrasonic and lightscattering data. These findings point towards a pressure-induced positive sound dispersion, with an associatedhigh-frequency sound velocity comparable to that of the polycrystalline sample at the same P.