Amorphization behaviors in polycrystalline alumina irradiated with energetic iodine ions

A cross-sectional transmission electron microscopy (XTEM) technique utilized in examining the sintered alumina (Al2O3) sample irradiated by 85.0 MeV iodine ions I7+ to 2.8x1018 m-2 reveals that almost complete amorphization takes place up to depths around 2 μm. Several grains including grains about to be fading out at depths of 2.5-3.5 μm are seen to have moved from the yet-amorphized region leaving the amorphized region behind. The amorphized regions extend up to depths around 4.5 μm for the sample irradiated to 12x1018 m-2. Any defect clusters cannot be observed in grains located at depths around 8 μm, where nuclear energy depositions are predicted to peak to about 1 dpa. The present results clearly demonstrate that the energy depositions through electronic process in alumina irradiated with heavy ions like present I7+ transform the crystalline phase into amorphous ones even near room temperatures, for accumulated electronic energy depositions above some 1.5-2 GGy with deposition rates above 4-5 keV/nm/ion