The vibrational dynamics of GeO2 at the glass transition: a Raman and Brillouin scattering study

New temperature-dependent Brillouin and Raman scattering experiments were performed on vitreous GeO2 in the 10-1200K temperature range. We found that, while the sound velocity above room temperature slightly increases (2-3%), the frequency of the Boson peak maximum shows unexpected behavior, decreasing by more than 15% when the temperature is increased. The results are interpreted in the framework of a phenomenological model.