Chemical imaging and diffusion of hydrogen and lithium in lithium aluminate

Tritium (3H) must be replenished for strategic stockpile and fusion reactors. 6Li-enriched γ-LiAlO2 pellets have been used for 3H production by thermal neutron irradiation. A fundamental study of 3H and 6Li diffusion processes in irradiated γ-LiAlO2 pellets is needed to assess and predict the long-term material performance. This study focuses on identifying the trapping sites and diffusion pathways of 1H (a surrogate for 3H) and Li atoms in polycrystalline γ-LiAlO2 pellets irradiated with both 4He+ and 1H2+ ions. A combination of STEM-EELS, Nano-SIMS and APT is employed for chemical imaging at nanoscale resolution. There is direct evidence for preferred Li diffusion pathways along grain boundaries. Isolated voids are identified as possible Li trapping sites in the irradiated γ-LiAlO2 pellets. Possible lithium hydrides and/or hydrates are precipitated on the surface of the irradiated pellets. This study improves our understanding of H and Li diffusion processes and provides data for modelling and simulation to predict material performance during neutron irradiation of γ-LiAlO2 pellets.