Deuterium diffusion in γ-LiAlO2 pellets irradiated with He+ and D2+ ions

Abstract

Sequential irradiations of polycrystalline γ-LiAlO2 pellets were performed at 573 K with He+ and D2+ ions to overlap the deuterium (D) profile with the He+ ion damage peak. The D depth profiles were measured using time-of-flight secondary ion mass spectrometry before and after thermal annealing steps. A linear concentration gradient approximation model is proposed to estimate the diffusion coefficient. The combined isothermal and isochronal data are used to determine the activation energy for D migration. At and above 1 × 1017 He++D+/cm2, a double-peak structure in the D profile is observed probably due to isotope exchange reactions with H2O and H2. The D diffusion coefficient in the irradiated γ-LiAlO2 pellets is on the order of 10−12 cm2/s at 773 K for the first 2 min annealing and the average values between 5 and 60 min tend to decrease to 10−13 or 10−14 cm2/s, depending on the ion fluence. The activation energy for D migration is determined to be 1.0 ± 0.3 eV at 2 × 1016 He++D+/cm2 and 0.6 ± 0.3 eV at 1 × 1017 He++D+/cm2. The results from this study may help better understand and predict tritium diffusion behavior during neutron irradiation of γ-LiAlO2 pellets.