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

This study reports on the microstructural, phasic and compositional evolutions of gamma-LiAlO2 during ion irradiation. Polycrystalline gamma-LiAlO2 pellets were irradiated sequentially with He+ and D-2(+) ions to the same combined fluences of up to 3 x 10(17) (He++D+)/cm(2) 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 x 10(16) (He++D+)/cm(2), followed by the formation of nano-sized precipitates and fractures at higher doses. Spinel-like precipitates of nonstoichiometric LiAl5O8 and gas-filled cavities are observed to grow with increasing dose. Faceted precipitates and rounded cavities appear at 2 x 10(17) (He++D+)/cm(2). With further increasing ion fluence to 3 x 10(17) (He++D+)/cm(2), 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 gamma-LiAlO2 pellets during the microstructural evolution. In the precipitate and amorphized regions, Li concentrations decrease to similar to 7 and 3.7 at.% from 25 at.% in gamma-LiAlO2, respectively. This study reveals a full-cycle microstructural evolution with corresponding compositional changes in gamma-LiAlO2 pellets during ion irradiation at 773 K. The data could help model, assess, and predict the material performance during neutron irradiation in reactors.