Cluster self-organization of intermetallic systems: Nanocluster precursors (i-K8, i-K6, K4) and self-assembly of crystal structures Ir8Mg58(cF396), Ir7Mg44(cF408), and Ir6Mg26 (hR96)

Abstract

Suprapolyhedral cluster precursors Kn with a hierarchical structure (with the number of polyhedra n = 4, 6, 8) have been derived and their topological representation as bichromatic graphs has been performed. With the use of computer methods (the TOPOS program package), combinatorial-topological analysis of icosahedral monster structures of close compositions Ir8Mg58 (cF396, F\( \bar 4 \)3m, V = 8139 A3) and Ir7Mg44 (cF408, F\( \bar 4 \)3m, V = 8117 A3) has been performed. Suprapolyhedral nanoclusters consisting of eight and six Ir icosahedra (nanoclusters i-K8 and i-K6 comprising 86 and 50 atoms) have been identified by the method of complete decomposition of the 3D factor graph of crystal structures into cluster substructures in Ir7Mg44. In Ir8Mg58, the i-K8 nanocluster is retained, whereas the i-K6 cluster is substituted by the K4 nanocluster composed of four Ir polyhedra with CN = 9 comprising 34 atoms. Complete 3D reconstruction of the self-assembly mechanism of crystal structure has been carried out by the scheme nanocluster precursor-primary chain-microlayer-microframework. It has been demonstrated that the voids in the Ir8Mg58 and Ir7Mg44 frameworks accommodate tetrahedral cluster spacers T-Mg(Mg4) and T-Mg4, respectively. The Ir6Mg26 structure (hR96, R\( \bar 3 \)c, V = 1890 A3) is made of the suprapolyhedral cluster K6 formed by six Ir polyhedra with CN = 11 and comprising 50 atoms; in this case, the structure contains no cluster spacers. In all structures, nanoclusters retain their own symmetry (\( \bar 4 \)3m for i-K8, i-K6, and K4 and \( \bar 3 \) for K6).