High frequency sound is observed in lithium diborate glass, Li2O-2B2O3, using Brillouin scattering of light and x rays. The sound attenuation exhibits a nontrivial dependence on the wave vector, with a remarkably rapid increase towards a Ioffe-Regel crossover as the frequency approaches the boson peak from below. An analysis of literature results reveals that the boson-peak frequency is closely related with a Ioffe-Regel limit for sound in many glasses. We conjecture that this relation, specific to glassy materials, might be rather common among them.

International audienceCharacterisation of uranium oxides in different conditions is a challenge both in nuclear and environment sciences. We focus here on U4O9, which is a superstructure of UO2. Homogeneous U4O9 powder was fabricated and characterised by Raman spectroscopy. The Raman spectrum of a pure-phase U4O9 is, for the first time, completely described and interpreted. U4O9 Raman spectrum derives from the well characterised one of UO2. Besides reminiscent modes of UO2, a band at 630 cm-1, which has a specific response to polarised light, was interpreted as characteristic of clusters of interstitial oxygen atoms. These experimental data will help to rationalise the interpretation of UO2 damaged samples

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