Regensburg 2007 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 24: Poster I

DY 24.17: Poster

Wednesday, March 28, 2007, 16:00–18:00, Poster D

Lattice dynamics of polycrystalline Beryllium — •Irmengard Fischer, Alexei Bossak, and Michael Krisch — European Synchrotron Radiation Facility, BP220, F-38043 Grenoble Cedex, France

The phonon dispersion along high-symmetry directions of a single crystal gives access to a large range of physical properties such as electron-phonon coupling, anharmonicity, specific heat, sound velocities and elastic constants. Novel materials and crystals under extreme conditions are, however, often only available as polycrystals, and consequently investigations are limited to orientationally averaged properties such as the phonon density of states (PDOS) and the average sound velocity. To overcome these limitations, we developped a method to extract the single crystal phonon dispersion from inelastic x-ray scattering (IXS) measurements of a polycrystalline material. We chose as test case Be, because of its well known dispersion and its high IXS efficiency. The spectra were recorded with an energy resolution of 3 meV spanning the 2-80 nm-1 momentum transfer range. The experimental IXS spectra were fitted with a least-square routine using a Born - von Karman model, starting from a known set of force constants. The refined dispersion is in remarkable agreement with inelastic neutron measurements. Furthermore, the reconstructed PDOS is in excellent agreement with calculations, thus allowing the precise determination of macroscopic parameters such as the Debye temperature, the vibrational contribution to the specific heat and the internal energy. This novel application of IXS promises to be a valuable spectroscopic tool in cases where single-crystalline materials are not available.