International audienceWe measured the phonon dispersions in vanadium along the principal symmetry directions using inelastic x-ray scattering. Our data complement previous results derived from thermal diffuse scattering and clearly reveal several phonon-dispersion anomalies, as well as pronounced variations of the phonon widths. Electronic structure calculations, more specifically, an analysis in terms of Fermi-surface spanning vectors allow the qualitative association of these anomalies with the topology of the Fermi surface, thus highlighting the impor- tance of electron-phonon coupling

The inelastic x-ray scattering from polycrystalline materials at low momentum transfer is analyzed with respect to the orientation-averaged acoustic phonon dispersion and the relationship between the derived sound velocities and their corresponding macroscopic entities. The effect of texturing on the sound dispersion is discussed and illustrated using the examples of hcp cobalt and hexagonal graphite. Our theoretical considerations are supported by experimental results and emphasize the importance to carefully consider the effects of elastic anisotropy when data obtained by inelastic x-ray scattering are compared or confronted with macroscopic measurements.

[1] We have retrieved the full lattice dynamics of stishovite, SiO 2 , by a combination of powder inelastic x-ray scattering (IXS) and ab initio calculations. The extracted dispersion curves are confirmed by experiments on a single crystal. Thereby we have shown that IXS powder measurements over a large range of momentum transfers allow an unambiguous validation of lattice dynamics models, which then in turn can be used to derive elastic and thermodynamic properties. The proposed method can be extended to high pressure measurements on in situ synthesized samples and promises to be a valuable tool in studies of materials for which no single crystals can be obtained.

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