STRUCTURE OF NACD2 - AN ALTERNATIVE PATH TO A TRIAL STRUCTURE

A new derivation of a trial structure of the NaCd2 compound is describ ed. 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 t his form the initial assumption is made that the structure is tetrahed rally close-packed and that the coordination polyhedra are all the usu al with coordination numbers 12, 14, 15 and 16, respectively. These re strictions are first invoked in the search for the correct structural arrangements along the symmetry axes. Only those arrangements are cons idered which have small packing strains along these axes when calculat ed using the metallic radii for coordination number 12.