BODY-CENTERED CUBIC - A CLOSE-PACKED STRUCTURE

It need not be considered surprising that many metals attain and retain the b.c.c. structure at very high pressures, since there is a sense in which this structure is close packed (emphatically closer than f.c.c.), namely in the sense of putting nuclei close to every point of the space in which the array of nuclei resides. Closeness in this sense, it is suggested, is particularly relevant to the structure of metals, which are not assemblies of hard spheres. The case is presented by way of a consideration of Voronoi cells, which provide a straightforward way of testing for closeness in this sense for any array.