High frequency acoustic modes in vitreous beryllium fluoride probed by inelastic x-ray scattering

Inelastic x-ray scattering measurements of the dynamics structure factor have been performed on vitreous beryllium fluoride (v-BeF2) at T=297 K in the momentum transfer, Q, range Q=1.5–10 nm−1. We find evidence of well defined high frequency acoustic modes. The energy position and linewidth of the excitations disperse with Q as ∝Q and ∝Q2, respectively, up to about one half of the first maximum of the static structure factor. Their magnitude compares favorably with low-frequency sound velocity and absorption data. The results indicate worth mentioning similarities of the high frequency collective dynamics of different network forming glasses such as v-B2O3 and v-SiO2.