Abstract: | A combinatorial and topological analysis of Li19Na8Ba15 (hP842, a = 20 ?, c = 93 ?, V = 33552 ?3, P
$
\bar 3
$
\bar 3
) has been performed using computer methods (the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters
about 20 ? in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete
decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed
2D layers 36, which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1
+ 16 + 59 + 103) with local symmetries 3 and $
\bar 3
$
\bar 3
, respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster
contains a 104-atom quasicrystal approximant (Samson cluster). |