A model relating diameters of atoms in non-spherical voids to unit-cell dimensions, applied to phases with the A15 and Cu2Mg structures

Abstract

A model is described which relates the diameters of atoms located in non-spherical voids to the unit-cell dimensions. It is applied to binary intermetallic phases with the tetrahedrally close-packed A15 and Cu₂Mg type structures. It treats situations in which several different interatomic distances from an atom to its neighbours in the surrounding Coordination polyhedron act together in controlling the cell dimension(s). The model derives its parameters from observed cell dimensions, but is then able to reproduce them effectively in terms of atomic diameters determined from elemental structures. Since it involves independent elemental atomic diameters, it provides a mechanism by which contacts between different atoms at different distances combine together to control the unit-cell dimensions. Examples of its application are given.