Microstructural and compositional evolutions in γ-LiAlO2 pellets during ion irradiation at an elevated temperature

Abstract

This study reports on the microstructural, phasic and compositional evolutions of γ-LiAlO2 during ion irradiation. Polycrystalline γ-LiAlO2 pellets were irradiated sequentially with He+ and D2+ ions to the same combined fluences of up to 3 × 1017 (He++D+)/cm2 at 773 K. The irradiated pellets were characterized using scanning transmission electron microscopy and atom probe tomography. Surface amorphization likely due to radiolysis and planar defects as a possible precursor for formation of precipitates are created at 5 × 1016 (He++D+)/cm2, followed by the formation of nano-sized precipitates and fractures at higher doses. Spinel-like precipitates of non-stoichiometric LiAl5O8 and gas-filled cavities are observed to grow with increasing dose. Faceted precipitates and rounded cavities appear at 2 × 1017 (He++D+)/cm2. With further increasing ion fluence to 3 × 1017 (He++D+)/cm2, amorphization of the precipitates takes place and micron-sized fractures appear. Surface exfoliation could occur at an extremely high ion fluence. There are compositional changes in the γ-LiAlO2 pellets during the microstructural evolution. In the precipitate and amorphized regions, Li concentrations decrease to ∼7 and 3.7 at.% from 25 at.% in γ-LiAlO2, respectively. This study reveals a full-cycle microstructural evolution with corresponding compositional changes in γ-LiAlO2 pellets during ion irradiation at 773 K. The data could help model, assess, and predict the material performance during neutron irradiation in reactors.