Dresden 2009 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 20: Poster Session I
MM 20.20: Poster
Tuesday, March 24, 2009, 14:45–16:30, P4
Polarization dependent Raman spectroscopy of LiBH4 single crystals — •Britta Willenberg, Florian Gebert, and Joachim Schoenes — Institut für Physik der Kondensierten Materie, TU Braunschweig, 38106 Braunschweig, Germany
In a previous paper [1] we have reported an extensive low temperature Raman scattering study on LiBH4 and LiBD4 powders. The 27 observed lines have been assigned to phonon modes within the orthorhombic Pnma structure by comparing the experimental values to density functional theory (DFT) values [1]. In the present contribution we present for the first time Raman scattering measurements on small LiBH4 single crystals. These have been identified among the grains of the powders (Alpha Aesar) by searching for large polarization dependencies of the Raman lines. On the basis of these new results a few of the former assignments have to be revised. Among the external modes this concerns the mode near 307 cm−1 which is definitely of Ag symmetry and not of B2g symmetry as had been concluded on purely energy arguments.
A second issue is the phase transition to a hexagonal structure at about 380 K. Several grains of our powder samples did not show the anticipated changes of the Raman spectra. We have now succeeded in finding a few grains which, indeed, display the characteristic simplification of the Raman spectra when the phase transition to the hexagonal phase occurs.
[1] A.-M. Racu et al., J. Phys. Chem. A 112, 9716 (2008)