The irradiation damage response of MgO · 3Al 2O 3 spinel single crystal under high-fluence ion-irradiation

Non-stoichiometric single crystal spinel samples with composition MgO · 3Al ₂O ₃ were irradiated near (001) orientation with 400 keV Xe ⁺⁺ ions at 100 K to a dose of 1 × 10 ¹⁶ Xe/cm ², representing a peak damage level of 25 displacements per atom (dpa). Damage accumulation in the irradiated surface was assessed by cross-sectional transmission electron microscopy. A continuous crystalline layer was observed in the implanted region. The layer is oriented with the underlying substrate, but is highly defected and possesses a symmetry different than that of the bulk. This change in symmetry is revealed by the absence of diffracted intensity at first-order spinel reciprocal lattice positions. These results are compared with earlier observations on equimolar (001) MgO · Al ₂O ₃ single crystals irradiated with 400 keV Xe ⁺⁺ ions to the same dose and at the same temperature [N. Yu, K.E. Sickafus and M. Nastasi, Phil. Mag. Lett. 70(4) (1994) 235 (Ref. [1])].