Packing Characteristics of Atomic Structures of Model Icosahedral Phases

Abstract

Voronoi polyhedra and tetrahedra-octahedra packing analyses have been performed for atomic structures of two types of model icosahedral phases (I-phases), the Mackay icosahedron (MI) type and triacontahedron (TC) type. The structures have been constructed based on the models of Henley and Elser. In the TC-type I-phase, Voronoi volumes can be divided into large and small, and the structure consists mostly of tetrahedral units, indicating that this type of I-phase is a dense packing of two sizes of atoms. In the MI-type I-phase, no distinct separation of the distribution of the Voronoi volumes is seen, and the structure contains a large number of octahedral units, indicating that the MI-type I-phase alloys are not close packings of different-sized atoms. The compositions of existing I-phase alloys are discussed in relation to the above analyses.