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M: Metallphysik

M 18: Postersitzung

M 18.24: Poster

Dienstag, 9. März 2004, 14:30–16:30, Saal C

Non-icosahedral equilibrium surfaces of icosahedral Al-Pd-Mn quasicrystals — •Mariya Yurechko, Benjamin Grushko, Philipp Ebert, and Knut Urban — Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich

LEED and STM investigations of the structure of Al-Pd-Mn quasicrystal surfaces prepared with essentially identical preparation methods, yielded widely varying surface structures, even with different symmetries. We show on a basis of a precision determination of the ternary Al-Pd-Mn phase diagram, which of those surface structures are equilibrium surfaces of icosahedral quasicrystals and how they are formed. We find that the equilibrium surface of icosahedral Al-Pd-Mn quasicrystals can have non-icosahedral (i.e. decagonal and orthorhombic) structures, depending on the exact initial composition of the quasicrystal. Only in a narrow composition range of the icosahedral Al-Pd-Mn phase after annealing or under kinetically limited (non-equilibrium) cleaning procedures, icosahedral surfaces can be obtained. These effects are attributed to the phase equilibrium of the ternary alloy system.