Structure of NaCd2: an alternative path to a trial structure

Abstract

A new derivation of a trial structure of the NaCd₂ compound is described. It is based on the application of the stochastic method in a form which is particularly useful in the derivation of trial structures of intermetallic compounds of high crystal symmetry for which the radius ratios of the component metals are of the appropriate magnitudes. In this form the initial assumption is made that the structure is tetrahedrally close-packed and that the coordination polyhedra are all the usual 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.