Browsing by Author "Schilling, Rolf"

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    Intrinsic stability of quasicrystals under the generation of Frenkel pairs
    (1992) Roth, Johannes; Schilling, Rolf; Trebin, Hans-Rainer
    Under irradiation metastable quasicrystals undergo a phase transition to an amorphous state. This transition can be reversed by annealing. As in normal crystalline materials the phase transition is considered to be triggered by generation and recombination of vacancies and interstitial atoms (Frenkel pairs). We have classified the possible Frenkel defects in a metastable monatomic quasicrystal with respect to geometric and energetic properties. With numerical simulation we have studied the behaviour of the quasicrystal under a load of Frenkel defects for various defect concentrations. We find three ranges of behaviour: up to 5% defects per atom the structure remains icosahedral, in a middle range it stays disordered icosahedral or it becomes either disordered or perfect crystalline, depending on the implementation of the defects. If there are more than 10% defects the structure becomes irreversibly amorphous. We finally compare our results with experimental data.
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    Stability of monatomic and diatomic quasicrystals and the influence of noise
    (1990) Roth, Johannes; Schilling, Rolf; Trebin, Hans-Rainer
    The stability of quasicrystals endowed with atomic Lennard-Jones–like pair potentials was investigated with use of the method of steepest descent. Starting from two- and three-dimensional Penrose patterns, the basic units were decorated in various fashions with one or two sorts of atoms. In accord with previous studies, all monatomic two-dimensional quasicrystals decay to a hexagonal periodic crystal with defects; diatomic systems remain stable when the relative size of the atoms is suitably chosen. In three dimensions, the monatomic quasicrystalline unit-sphere packing was proven stable as well as the structure of truncated icosahedra, even if in the initial configuration the atoms were displaced statistically up to 7% and 25%, respectively, of the edge length (noise). A series of decorations (among them one involving Mackay icosahedra) relaxed to the amorphous state. In these transitions the atoms arrange in families of Fibonacci planes whose separations scale down to atomic distances in a self-similar fashion.