Irradiation effects and hydrogen behavior in H₂⁺ and He⁺ implanted γ-LiAlO₂ single crystals

Gamma-phase lithium aluminate (γ-LiAlO₂) is a breeder material for tritium, a necessary substance for strategic stockpile and fusion power systems. A fundamental study of structural evolution and tritium diffusion in γ-LiAlO₂ under displacive irradiation is needed to fully assess the material performance. This study utilizes ion implantation of protium (surrogate for tritium) and helium in γ-LiAlO₂ single crystals at elevated temperatures to emulate the irradiation effects. The results show that at 573 K there are two distinct disorder saturation stages to 1 dpa without full amorphization; overlapping implantation of H₂⁺ and He⁺ ions suggests possible formation of gas bubbles. For irradiation to 10²¹ H⁺/m² (0.36 dpa at peak) at 773 K, amorphization occurs at surface with H diffusion and dramatic Li loss; the microstructure contains bubbles and cubic LiAl₅O₈ precipitates with sizes up to 200 nm or larger. In addition, significant H diffusion and release are observed during thermal annealing. - Highlights: • Disorder saturation stages are observed in γ-LiAlO₂ irradiated with H₂⁺ ions at 573 K. • Li loss occurs during H₂⁺ ion implantation in γ-LiAlO₂ at elevated temperatures (573–773 K). • Both gas bubbles and cubic LiAl₅O₈ precipitates are formed in γ-LiAlO₂ irradiated with H₂⁺ ions at 773 K. • Isochronal annealing at temperatures up to 773 K leads to significant H release.