Polygonisation of ionic single crystals - A new effect of swift ion bombardment

Isostructural oxide single crystals of the fluorite structure: stabilized c ubic zirconia and UO2 were bombarded at room temperature with 72 MeV iodine ions or 340 MeV Xe ions, respectively. The aim of this paper was the study of structural transformations induced by ion bombardment in two different regimes: at 72 MeV where the radiation damage production is strongly influe nced by collision cascades and at higher energies where the ionization mech anism prevails. The structure of as-grown and implanted single crystals was examined using the RES/channeling technique and X-ray diffraction analysis . Some of the samples were also investigated by transmission electron micro scopy. It was observed that the residual damage depends strongly on energy loss mechanism, and hence on the incident ion energy. At high incident ener gies solidification of latent tracks in UO2 leads to their polygonisation. Since the energy of 72 MeV is too low for latent track formation, the resul ting damage is composed of dislocation and clusters and is similar to that created by the ion bombardment at low energies. The amount of defects was s trongly enhanced by the interaction of ionised regions with collision casca des.