PNNL

Abstract

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 D2+ ions to the same combined fluences of up to 3E17 (He++D+)/cm2 at 773 K. The irradiated pellets were characterized using scanning transmission electron microscopy (STEM) and atom probe tomography (APT). Planar defects form as a possible precursor for formation of precipitates at 5E16 (He++D+)/cm2, followed by formation of nano-sized precipitates and fractures at higher doses. Spinel-like precipitates of non-stoichiometric LiAl5O8 and cavities filled with gas are observed to grow with increasing dose. Faceted precipitates and rounded cavities appear at 2E17 (He++D+)/cm2. With further increasing ion fluence to 3E17 (He++D+)/cm2, amorphization of the precipitates takes place at the damage peak 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 ~7 and 3.7 at.% from 25 at.% in gamma-LiAlO2, respectively. This study reveals the irradiation behavior of gamma-LiAlO2 pellets and provides valuable data to assess and predict the material performance during neutron irradiation in reactors.