Effects of temperature and dose rate on ion-irradiated γ-LiAlO2 pellets

Defect accumulation and microstructural evolution during ion irradiation at elevated temperatures are governed by competing processes of defect production, driven by the dose rate, and defect recovery, controlled by diffusion, interaction, and annihilation. This study investigates the effects of irradiation temperature and the dose rate on microstructural evolution, deuterium retention, and lithium volatilization in γ-LiAlO2 pellets subjected to sequential He+ and D+ ion irradiation. Experiments were performed to a total fluence of 3 × 1017 (He+ + D+)/cm2 at 623, 673, 723, and 773 K with an average He+ dose rate of 7.7 × 10−4 dpa/s, and to 2 × 1017 (He+ + D+)/cm2 at 773 K with dose rates of 6.8 × 10−5, 2.9 × 10−4, and 7.3 × 10−4 dpa/s. At 623 K, the microstructure was dominated by cavities and fractures with no observable precipitate formation, while small precipitates emerged at 673 K. Increasing the irradiation temperature to 723–773 K promoted the formation of larger, faceted LiAl5O8 precipitates, and surface amorphization, accompanied by pronounced lithium depletion and H–D isotopic exchange. At 773 K, medium and high dose rates produced an amorphized surface layer over a crystalline subsurface containing LiAl5O8 precipitates and blisters at the crystalline–amorphous interface, whereas low-dose-rate irradiation preserved surface crystallinity with cavities distributed in the matrix, around precipitates, and along grain boundaries. Precipitate morphology was anisotropic with limited size dependence on the dose rate. These results elucidate the coupled effects of temperature and the dose rate and demonstrate that sequential He+ and D2+ irradiation at 773 K reproduces key microstructural features and H isotope behavior observed in neutron-irradiated γ-LiAlO2 at 573 K.