Regensburg 2013 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 13: Topical Session: Quasicrystals & Complex Metallic Alloys III

MM 13.4: Vortrag

Montag, 11. März 2013, 16:30–16:45, H25

Structure of a decagonal Al–Pd–Mn quasicrystal with 16 Å periodicity — Benjamin Frigan¹, Marek Mihalkovič², and •Hans-Rainer Trebin¹ — ¹Institut für Theoretische und Angewandte Physik, Universität Stuttgart, Germany — ²Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia

We present the first detailed structure solution for a decagonal quasicrystal in the Al–Pd–Mn system by means of ab initio energy minimization. It is based on structure models of the ε₆- and other approximant phases. All phases consist of columns of pseudo-Mackay icosahedra (PMI), whose projections form tilings of the plane. In between there are glue atoms in the form of large bicapped pentagonal prisms (LBPP). In the past, we have optimized the structure of the ε-phases, where the tilings consist of pentagons, hexagons and nonagons. These can be represented as subsets of a hexagon-boat-star (HBS) tiling. The decagonal phase comprises further HBS-tiles. We have constructed several HBS approximants and decorated them with PMI and LBPP clusters. Whereas the PMI clusters were kept essentially unchanged, each LBPP is adjusted in occupancy depending on its position in the various tiles. In this way we obtain cluster decorations for all tiles of the decagonal quasicrystal. The structures were optimized by molecular dynamics annealing with specially developed EAM-potentials, followed by further relaxation with ab initio calculations. The quality of the structures is judged by their position within the convex hull of stable, experimentally known phases of the Al–Pd–Mn phase diagram.