High-resolution transmission electron microscope analysis of irradiation-induced structural change in magnesium aluminate spinel compound

The present talk will give an overview of our recent result on irradiation-induced structural change in magnesium aluminate compound, which is known as a radiation tolerant oxide, especially to volumetric swelling. Magnesium aluminate spinel of MgO-nAl2O3 with n=1.1, was irradiated with swift heavy ions of 200 MeV Xe 14+ (Se=24 keV/nm) and 350 meV Au 28+ (Se=34 keV/nm) at a tandem ion-accelerator. Trnasmision electron microscopy techniques of high-resolution (HR) imaging. STEM dark-field imaging as well as high angular resolution electron channeling x-ray spectroscopy (HARECXS) were employed in quantitative analysis of irradiation-induced structur change. Dark spotty contrast appears at ion-track formed by swift-heavy irradiation in STEAM dark-field imaging, indicating lower dencity inside the ion-track. Clear lattice fringes are abserved in HR images even inside the ion-track in both Xe 14+ and Au 28+ irradited specimens. However, the fringe pattern inside the tracks is different from that appearing in the matrix, bein indicative of displace interinitials and a defective NaCl structure in formed after preferential evacuation of cations from the tetrahedral positions. Quantitative HERECXS analysis showd that cation disordering progressively with ion fluence. It was revealed that the disorder regions are extended over about 12 nm in diameter along that ion-tracks, which is much wider than the efective volume detected by HR image.