Asymmetry in Metals of Hexagonal Structure

Abstract

THE axial ratio, c/a, of the majority of metals having a hexagonal close-packed type of structure differs appreciably from the value 2 ” = 1·633 which corresponds to a hexagonal close-packed system of spheres. The two most notable deviations are for zinc and cadmium, for which c/a = 1·86 and 1·89 respectively, while for beryllium, titanium, zirconium, hafnium, yttrium, ruthenium and osmium, c/a lies between 1·58 and 1·59. These facts have sometimes been expressed by describing the atomic domains as having the forms of prolate and oblate spheroids when c/a is respectively greater than and less than 1·633 ; but it is only recently that experimental evidence has been obtained which throws light on the nature of the asymmetry in these metals.