Microstructural evolution and precipitation in γ-LiAlO2 during ion irradiation

Polycrystalline gamma-LiAlO2 pellets were sequentially irradiated with 120 keV He+ and 80 keV D-2(+) ions to the fluences of 1 x 10(17) and 2 x 10(17) (He+ + D+)/cm(2) at 573 K. Additional irradiation was performed to a fluence of 2 x 10(17) (He+ + D+)/cm(2) at 773 K. The irradiated pellets were characterized using scanning transmission electron microscopy, time-of-flight secondary ion mass spectrometry, and grazing incidence x-ray diffraction. 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 2 x 10(17) (He+ + D+)/cm(2) at 573 K. In contrast, faceted precipitates with sizes larger than 100 nm formed in a pellet irradiated to 2 x 10(17) (He+ + D+)/cm(2) 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 the dose increases, Li loss will continue and the precipitates will approach a composition of alumina primarily in phases of alpha-Al2O3 and amorphized Al2O3. (C) 2022 Author(s).