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SYEC: Materials under extreme conditions

SYEC 3: Extreme Conditions (Poster Session)

SYEC 3.5: Poster

Mittwoch, 26. März 2003, 13:00–19:00, P2a

Crystal structure and lattice dynamics of AlB₂ under pressure — •I. Loa¹, K. Kunc^1,2, K. Syassen¹, and P. Bouvier³ — ¹MPI für Festkörperforschung, D-70569 Stuttgart, Germany — ²CNRS and Université Pierre et Marie Curie, F-75252 Paris Cédex 05, France — ³European Synchrotron Radiation Facility, F-38043 Grenoble France

We have studied the effect of high pressures to 40 GPa on the crystal structure and lattice dynamics of AlB₂ by synchrotron x-ray powder diffraction, Raman spectroscopy, and first-principles calculations. There are no indications of a pressure-induced structural phase transition. The Raman spectra of the metallic sample exhibit a well-defined peak near 980 cm⁻¹ at 0 GPa which can be attributed to the Raman-active E_2g zone-center phonon. Al deficiency of ∼11% in AlB₂, as indicated by the x-ray data, changes qualitatively the electronic structure, and there are indications that it may have a sizable effect on the pressure dependence of the E_2g phonon frequency. Similar changes of the pressure dependence of phonon frequencies, caused by non-stoichiometry, are proposed as an explanation for the unusually large variation of the pressure dependence of T_c for different samples of the superconductor MgB₂.