Microstructure and atomic disordering of magnesium aluminate spinel irradiated with swift heavy ions

Abstract

We have investigated the microstructure and atomic disordering of nearly stoichiometric magnesium aluminate spinel (MgO·1.1Al2O3), irradiated with 200MeV Xe14+ ions (Se=25keV/nm). Transmission electron microscopy techniques of bright-field (BF) and high-resolution (HR) imaging, as well as high angular resolution electron channeling X-ray spectroscopy (HARECXS) were employed for quantitative analysis of radiation-induced structural change. BF images of ion tracks show columnar dark contrast of ∼4nm in diameter accompanying distinct black or white dots at the incident surface. Clear lattice fringes are observed in HR images even inside the ion tracks, indicating that the spinel crystals are not amorphized but partially disordered along the ion tracks. HARECXS analysis showed that cation disordering progresses successively with ion fluence, and the disordered regions are found to extend over 12.8±0.9nm in diameter for Al ions and 9.6±0.6nm for Mg ions along the ion tracks. This chemically disordered region is much larger than the strained volume detected by BF and HR images.