X-ray and neutron scattering studies in vitreous silica: acoustic nature of vibrational dynamics in the mesoscopic range

We report X-ray and neutron scattering results in vitreous silica. As in earlier data, clear evidence is found for sound wave modes at the energies of the boson peak. We have observed by X-ray experiments a clear dispersion of Brillouin peaks and we have detected experimental evidence of inelastic scattering in the second Brillouin zone. By neutron scattering experiments we have found coherence effects in S(Q, E). These effects are consistent with average acoustic phonon dispersion curves, which are similar in character to the dispersion curves found in crystals but, obviously, broadened by the topological disorder.