Local Atomic Configurations in Intermetallic Crystals: Beyond the First Coordination Shell

We have used a combined geometrical-topological approach to analyze 21,697 intermetallic crystal structures stored in the Inorganic Crystal Structure Database. Following a geometrical scheme of close packing of balls, we have considered the three most typical polyhedral atomic environments of the icosahedral, cuboctahedral, or twinned cuboctahedral shape as well as multi shell (up to four shells) local atomic configurations (LACs) based on these cores in 10,657 unique crystal structure determinations. In total, half of intermetallic structures have been found to contain one of these configurations, with the icosahedral LACs being the most frequent. We have revealed that even a two-shell configuration strongly predetermines the overall connectivity (topological type) of an intermetallic crystal structure. The chemical and stoichiometric composition of the multi-shell LACs generally obeys the close-packing model: the number of atoms in the subsequent shells (Nk) varies around the value Nk = 10k(2) + 2, which is valid for the same size atoms, to reach the densest packing for the kth shell. Deviations from the revealed regularities often indicate inconsistencies in the crystallographic information, unusual features of the structure, or the existence of more stable phases that can be used for the validation of experimental and modeling data.

Automated summary

We analyzed 21,697 intermetallic crystal structures using a combined geometrical-topological approach. Three typical polyhedral atomic environments (icosahedral, cuboctahedral, or twinned cuboctahedral shape) and multi shell local atomic configurations (LACs) were considered. We found that half of the intermetallic structures contain one of these configurations, with icosahedral LACs being the most frequent. Two-shell configurations strongly determine the overall connectivity of an intermetallic crystal structure.