The sigma phase revisited: an alternative pathway to a trial structure

摘要

A new derivation of a trial structure of the sigma phase is described. It is based on the stochastic method in a form which is particularly useful in the derivation of trial structures of high symmetry, provided that the radii of the component metals are of the appropriate relative magnitudes. In this form the initial assumption is made that the structure is tetrahedrally close-packed and that the coordination polyhedra are normal with coordination numbers 12, 14, 15 and 16, respectively. These restrictions are first invoked in the search for the correct structural arrangements along the symmetry axes. Only those arrangements are considered which have small packing strains along these axes when calculated using the metallic radii for coordination number 12.