A Large Dodecahedral Cluster Containing about 480 Atoms in a 2/1 Cubic Crystalline Approximant

A dodecahedral atom cluster, which is the largest atom cluster with icosahedral symmetry found in crystalline alloy phases, was observed in the cubic crystalline phase of β-(AlPdMnSi), referred to as a 2/1 approximant of an icosahedral quasicrystal, with a lattice constant of 2.0211 nm. The large dodecahedral cluster has a diameter of about 2.6 nm and contains about 480 atoms. The atomic arrangement of the dodecahedral cluster is divided into atomic shells with icosahedral symmetry, and most of the atoms in the shells are located at special positions associated with the golden mean in the three-dimensional Penrose lattice. A small icosahedral atom cluster, formed with twelve Al atoms at the vertices and a Pd atom at the center, is located at each vertex of a dodecahedral shell with a diameter of about 2 nm. The large dodecahedral atom cluster is considered to be an important cluster for understanding the structure of an Al-Pd-Mn icosahedral quasicrystal.