Grain boundary effects on radiation damage and tritium diffusion in Li–Al–O ceramics from molecular dynamics and experiments

Understanding irradiation damage and tritium transport in LiAlO 2 ceramics is essential for their deployment in tritium-producing burnable absorber rods (TPBARs). Grain boundaries (GBs) play an important role in governing radiation response and tritium transport in LiAlO 2 and its secondary phase LiAl 5 O 8 . Using molecular dynamics simulations, we investigated defect evolution and tritium diffusion during displacement cascades in single-crystal and bicrystal LiAlO₂ and LiAl₅O₈ at 600 K. The results reveal that GBs suppress the damage in the LiAlO 2 bicrystals as compared to single crystals, via interstitial emission. The effect is more pronounced for Li defects, than for Al and O. In LiAl₅O₈, the damage reduction due to the introduction of GB is less pronounced overall. Tritium diffusion coefficients at GBs are higher by factors of 2–10 relative to diffusion inside the grain bulk. The effect is particularly pronounced in LiAlO₂, where Σ5, Σ17, and Σ25 GBs promote rapid tritium transport, whereas LiAl₅O₈ exhibits slower diffusion due to reduced free volume at its GBs. These findings evince a trade-off that while GBs mitigate radiation damage by absorbing interstitials, they simultaneously provide fast pathways for tritium migration, which is not desirable for TPBAR application. The mechanistic insights gained here establish a foundation for microstructural design strategies to balance radiation tolerance and tritium retention in ceramic breeder materials.