PNNL

Abstract

Polycrystalline gamma-LiAlO2 pellets were sequentially irradiated with 120 keV He+ and 80 keV D2+ ions to the fluences of 1E17 and 2E17 (He++D+)/cm2 at 573 K. Additional irradiation was performed to 2E17 (He++D+)/cm2 at 773 K. The irradiated pellets were characterized using scanning transmission electron microscopy (STEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and grazing incidence X-ray diffraction (GIXRD). Lattice damage, amorphization and fractures are observed with no evidence for the formation of secondary-phase precipitates in the pellets irradiated up to an ion fluence of 2E17 (He++D+)/cm2 at 573 K. In contrast, faceted precipitates with sizes larger than 100 nm formed in a pellet irradiated to 2E17 (He++D+)/cm2 at 773 K. Analyses of the diffraction and composition data suggest that the precipitates have a spinel-type structure, likely a non-stoichiometric LiAl5O8 with Li depletion. This could be an intermediate phase with Li atoms at the octahedral and possibly tetrahedral sites as well. It is speculated that as dose increases, Li loss will continue and the precipitates will approach to a composition of alumina in mixed phases of gamma-Al2O3 and amorphized Al2O3.