Faulted defect aggregates in neutron-irradiated MgAl₂O₄ spinel

Single crystals of stoichiometric MgAl2O4 spinel were neutron-irradiated to fluences (> 0.1 MeV) of 2.8 x 1025 n m-2 (~ 1.5 dpa) at 1015 K and ~ 1.9 x 1026 n m-2 (~ 10 dpa) at 925 K and 1100 K. The resulting point defect aggregates were investigated using bright-field and weak-beam dark-field transmission electron microscopy. For the higher dose, faulted interstitial Frank dislocation loops were found on {110} and {111} planes with b = 1/4 <110> (cation fault) and b = 1/6 <111> (anion + cation fault) respectively. The latter preserves stoichiometry only for a randomized cation distribution.