It was recalled that voids appeared in solids which were exposed to particle irradiation at high temperatures. In hexagonal metals with c/a lattice parameter ratios that were smaller than that required for ideal close-packing, voids were observed (after high-dose irradiation) that were arranged in layers which were parallel to the basal plane. More perfect void ordering (such as the formation of void lattices, as in cubic metals) was not observed. It was shown here that it was the 2-dimensional diffusion of self-interstitial atoms in the basal plane which gave rise to the layer-type arrangement of voids. The possibility of other void-ordering phenomena in hexagonal metals was investigated. It was demonstrated that, under certain conditions, 1-dimensional diffusion of a metastable self-interstitial configuration could lead to the arrangement of voids in columns that were perpendicular to the basal plane.

T.Klemm, W.Frank: Applied Physics A, 1996, 63[1], 19-29