Cluster self-organization of crystal-forming systems: Suprapolyhedral cluster precursors and self-assembly of the icosahedral structure of ZrZn22(cF184) |
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Authors: | G. D. Ilyushin V. A. Blatov |
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Affiliation: | (1) Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskiĭ pr. 59, Moscow, 119333, Russia;(2) Samara State University, ul. Akademika Pavlova 1, Samara, 443011, Russia |
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Abstract: | The mechanism of self-assembly of symmetrically and topologically different chains and microlayers (in the form of planar nets) from cyclic three-node clusters A 3 is considered in the model system. The obtained nets correspond to the uninodal Shubnikov nets N 3 12 12 and N 3 6 3 6 and the new binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2). A complete three-dimensional reconstruction of the self-assembly of the icosahedral structure of the ZrZn22 compound (cF184) is performed using computer methods (with the TOPOS program package) according to the following scheme: cluster precursor → primary chain → microlayer → microframework (supraprecursor) → ... → framework. It is revealed that the suprapolyhedral cluster precursor (nanocluster ~12 Å in size) of the AB 2 composition is formed by three polyhedra shared by vertices in a cyclic manner: the A-ZrZn16 polyhedron (sixteen-vertex polyhedron with the point symmetry (bar 4)3m) and two B-ZrZn12 polyhedra (icosahedra with the point symmetry (bar 3) m). The AB 2 cluster precursor in the structure retains the symmetry m. It is established that the structural mechanism of self-assembly of the two-dimensional layer in the ZrZn22 structure is described by the binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2) constructed in the modeling. |
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