Regensburg 2002 – scientific programme

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M: Metallphysik

M 19: Symposium on Structurally Complex Alloy Phases I (SCAP I)

M 19.2: Talk

Thursday, March 14, 2002, 10:00–10:30, H16

Stability and dynamics of quasicrystals and intermetallic approximants — •Hans-Rainer Trebin — Institut für Theoretische und Angewandte Physik der Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart

In this review static and dynamic physical properties of quasicrystals and intermetallic approximants are surveyed in relation to structural features. Central focus of interest is the question: What is the origin of the long-range quasiperiodic order or of a periodic order with extremely large unit cells? There are many proposals under discussion: From steric causes (right atomic sizes) via entropic stabilization to cluster formation with overlap rules. Also evidence is growing that the Hume-Rothery rule, i.e. matching of the Fermi sphere with reciprocal lattice vectors, in combination with p-d-hybridization of electronic states is a prominent stabilization factor. It lowers energy by producing a pseudo-gap. Electron and phonon dynamics are dominated by multiply back-folded Brillouin- or Jones-zones, leading to flat bands and localization, most probably in the form of cluster resonances. The phason degree of freedom is special to these systems. It influences diffusive transport, dislocation motion and crack propagation. Currently intensive efforts are being made to observe coherent phason propagation.