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 = 10k2 + 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.