Topological Analysis and Structural Role of Silicon Motifs in Metal Silicides

Abstract

We have applied a combination of topological models and methods to analyze and classify 1464 crystal structures of inorganic metal silicides. To describe the connectivity of the structures, we have used the model of periodic net and arranged all structures into 112 topological types, each of which corresponds to a topologically distinct net. Separately, we have classified substructures of connected silicon atoms and distinguished 41 3-periodic, 29 2-periodic, 19 1-periodic, and 23 molecular motifs. We have found honeycomb and squarelattice 2-periodic motifs to be templates for assembling more complicated 2-periodic and 3periodic silicon substructures. Topological relations between substructures of other periodicities as well as between silicides and borides were also explored. The sizes of metal atoms in the silicon environment were estimated by using their Voronoi polyhedra. Free space in the clathrate silicides was represented with the natural tiling model, and the sizes of the cages in the clathrate silicon framework were found to fit the Voronoi-estimated sizes of metal atoms. Based on this correspondence as well as on the topological relation of the clathrate and zeolite frameworks, we have generated novel hypothetical zeolitic clathrate silicides KSi 9 (zeolite FERbased) and KSi 15 (zeolite PCR-based) and proved their stability by DFT modeling. A number of topological and geometrical conditions were formulated for modeling framework silicides based on other porous motifs.