Molecular dynamics simulations of displacement cascades in LiAlO₂ and LiAl₅O₈ ceramics

Molecular dynamics was employed to investigate the radiation damage due to collision cascades in LiAlO₂ and LiAl₅O₈, the latter being a secondary phase formed in the former during irradiation. Atomic displacement cascades were simulated by initiating primary knock-on atoms (PKA) with energy values = 5, 10 and 15 keV and the damage was quantified by the number of Frenkel pairs formed for each species: Li, Al and O. The primary challenges of modeling an ionic system with and without a core-shell model for oxygen atoms were addressed and new findings on the radiation resistance of these ceramics are presented. The working of a variable timestep function and the kinetics in the background of the simulations have been elaborated to highlight the novelty of the simulation approach. More importantly, the key results indicated that LiAlO₂ experiences much more radiation damage than LiAl₅O₈, where the number of Li Frenkel pairs in LiAlO₂ was 3-5 times higher than in LiAl₅O₈ while the number of Frenkel pairs for Al and O in LiAlO₂ are ~ 2 times higher than in LiAl₅O₈. The primary reason is high displacement threshold energies (E_d) in LiAl₅O₈ for Li cations. The greater E_d for Li imparts higher resistance to damage during the collision cascade and thus inhibits amorphization in LiAl₅O₈. The presented results suggest that LiAl₅O₈ is likely to maintain structural integrity better than LiAlO₂ in the irradiation conditions studied in this work.