Kazuhiro Yasuda, Tomokazu Yamamoto, Motoki Etoh, Shinji Kawasoe, Syo Matsumura, Norito Ishikawa
May 18, 2013
Accumulation and recovery of radiation-induced damage with swift heavy ions in stoichiometric magnesium aluminate spinel, MgAl 2 O 4 , has been investigated. Microstructural change and atomic disordering was examined through transmission electron microscopy (TEM) techniques, with bright-field (BF) and high-resolution (HR) TEM images, and high angular resolution electron channelling X-ray spectroscopy (HARECXS), for single crystal MgAl 2 O 4 irradiated with 200 MeV Xe, and 340 or 350 MeV Au ions. The density of core damage region, detected by BFTEM with Fresnel-contrast, increased proportionally with ion fluence at the early stage of accumulation and saturated at a fluence higher than 10 16 ions m 2 . This result is discussed with a balance between the formation and recovery of the core damage region under irradiation, and the influence region to induce the recovery was evaluated to be 7 – 9 nm in radius. HARECXS and electron diffraction analysis revealed that cations at tetrahedral sites preferentially occupy octahedral sites to transform to defective rock-salt structure. The structure of the core damage region is found from HR and BFTEM images to be a columnar vacancy-rich region with a low atomic density.