Berlin 2012 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 57: Complex Materials I
MM 57.4: Vortrag
Donnerstag, 29. März 2012, 16:30–16:45, H 1029
Role of phason fluctuations for the stability of a quasicrystal model system — •Alexander Kiselev1, Michael Engel2, and Hans-Rainer Trebin1 — 1Institut für Theoretische und Angewandte Physik, Universität Stuttgart, Germany — 2Department of Chemical Engineering, University of Michigan, USA
The source of stability of quasicrystals is generally not well understood. A common model assumes that structural fluctuations, which are not present in periodic approximant crystal structures, play an important role by contributing a configurational term to the free energy. Here, we study the influence of phason fluctuations on the stability of a decagonal quasicrystalline model system, where the atoms interact by the Lennard-Jones-Gauss potential [1], and apply molecular dynamics and Monte Carlo simulations. Absolute values of the Free energy were calculated by the Frenkel-Ladd method [2] for the phononic part and by the phason flips decoupling approach for the configurational part. A phase transition from an energetically stabilized periodic Xi-approximant to an entropically stabilized random tiling quasicrystal is observed. We simultaneously have observed the phason elastic constants. One phason elastic constant changes its sign from positive to negative when the temperature at the Xi-quasicrystal transition is lowered, indicating a soft-phason transition.
[1] M. Engel and H.-R. Trebin, Phys. Rev. Lett. 98 225505 (2007)
[2] D. Frenkel and A.J.C. Ladd, J. Chem. Phys. 81 3188-3193 (1984)