Abstract
We report coherent inelastic neutron scattering results in vitreous silica at temperatures up to 1673 K, 200 K above the glass transition. As in earlier low-temperature data, clear evidence is seen for non-sound-wave modes at the boson peak. Contrary to other glass formers, silica shows nearly no fast relaxations at the glass transition. The combination of the neutron spectra with recent X-ray Brillouin data allows the identification of the scattering mechanisms for high-frequency sound waves in the glass. Below 1 THz, one has resonant scattering from low-frequency vibrations and above 1 THz, Rayleigh scattering from the atomic disorder.