Berlin 2005 – wissenschaftliches Programm

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M: Metallphysik

M 11: Symposium Complex Metallic Alloys III

M 11.2: Vortrag

Freitag, 4. März 2005, 17:45–18:00, TU H1058

The phasonic degree of freedom in the Ξ-Al-Pd-Mn phases: Metadislocations and phasonic phase boundaries — •Michael Engel und Hans-Rainer Trebin — Universität Stuttgart, Institut für Theoretische und Angewandte Physik, 70550 Stuttgart

One of the properties which distinguishes complex metallic alloys from ordinary metallic alloys is the possibility of spatial rearrangements of the cluster substructure resulting in new unit cells. Such rearrangements are discrete degrees of freedom, well known for another class of complex metallic compounds, quasicrystals, which can be seen as CMAs with infinite unit cells. By adopting quasicrystal terminology, the degrees of freedom are called phasonic degrees of freedom.

We demonstrate that the Ξ-(AlPdMn)-phases ξ, ξ′, and ξ′_n can be modelled by a simple projection formalism in three-dimensional hyperspace. It follows that in the ξ′_n-phases there is one phasonic degree of freedom, whose excitation results in a movement of structural defects, so-called phason-planes. Furthermore we describe phasonic phase boundaries between different Ξ-phases and metadislocations, which are special textures of partial dislocations. Both are modelled geometrically in the hyperspace and compared to HREM images from the literature. We determine the metadislocations of lowest energy and relate them uniquely to experimentally observed ones. Since moving metadislocations in the ξ′-phase create new phason-planes, we suggest a dislocation induced phase transition from ξ′ to ξ′_n.