Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 39: SYM Hydrogen in Materials: New Developments III
MM 39.4: Vortrag
Donnerstag, 28. Februar 2008, 15:20–15:40, H 1058
Refinement of the phonon analysis in the complex hydride systems LiBH4 and LiBD4 — •Ana Maria Racu1, Joachim Schoenes1, Zbigniev Lodziana2, Andreas Borgschulte2, and Andreas Züttel2 — 1Institut für Physik der Kondensierten Materie, Technische Universität Braunschweig, Germany — 2EMPA Materials Sciences and Technology, Div. Hydrogen and Energy, Dübendorf, Switzerland
In the present study we have performed low temperature micro Raman measurements on small LiBH4 and LiBD4 crystals. At the lowest temperature, the spectra compare very well with the calculated phonons for the orthorombic structure. The spectra are dominated by three separated bands: the external modes, the internal bending and the internal stretching vibrations. Internal refers to vibrations within the BH4− tetrahedra while external modes imply motions of Li+ and BH4−. The temperature dependence of the observed phonons corroborates the strong anharmonicity of the system. Due to the anharmonicity, Fermi resonances occur between the first order stretching modes and the second order bending modes of LiBH4. Moreover, the linewidths have an Arrhenius-like component, with an activation energy of 40 meV. This value corresponds to the energy of the librational mode determined by inelastic neutron scattering [1] and is strongly related to the reorientation motions of the BH4− tetrahedra.
[1] J. Tomkinson, T. C. Waddington, J. Chem. Soc. Faraday Trans 2 72, 528 (1976).