Microstructural and compositional evolutions in -LiAlO2 pellets during ion irradiation at an elevated temperature
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This study reports on the microstructural, phasic and compositional evolutions of -LiAlO2 during ion irradiation. Polycrystalline -LiAlO2 pellets were irradiated sequentially with He+ and D2+ ions to the same combined fluences of up to 31017 (He++D+)/cm2 at 773K. 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 51016 (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 21017 (He++D+)/cm2. With further increasing ion fluence to 31017 (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 -LiAlO2 pellets during the microstructural evolution. In the precipitate and amorphized regions, Li concentrations decrease to 7 and 3.7at.% from 25at.% in -LiAlO2, respectively. This study reveals a full-cycle microstructural evolution with corresponding compositional changes in -LiAlO2 pellets during ion irradiation at 773K. The data could help model, assess, and predict the material performance during neutron irradiation in reactors.
