Modeling of self-organization processes in crystal-forming systems.Structural mechanism of self-assembly of zirconosilicate Na_2ZrSi_2O_7 from supra polyhedral clusters

摘要

Topological analysis of the crystal structure of Na_2ZrSi_2O_7(parakeldyshite,space group P1)with an MT framework,where M are ZrO_6 octahedra and T are SiO_4 tetrahedra,was carried out by the method of coordination sequences(TOPOS.3.2 program package),and the self-organization of this structure was modeled.The cyclic-type suprapolyhedral cluster precursor Na_2M_2T_4 with the local symmetry T was identified by bicolor decomposition of the 4646+664 net.The cluster is composed of six polyhedra with two Na atoms located in the center.The precursors control the evolution of high-level crystal-forming clusters.The cluster coordination number is six.The centers of eight cluster precursors in the superprecursor of the Na_2ZrSi_2O_7 structure are related by translation vectors.