Fundamental Studies of Tritium Diffusivity in Irradiation Defective LiAlO₂ and Li₂ZrO₃: A Frist Principles Density Function Theory Study

The thermal neutron irradiation of lithium isotope (⁶Li) in tritium (³H) -producing burnable absorber rods (TPBARS) of LiAlO₂ and Li₂ZrO₃ crystal produces vacancies, defects of its constituent elements, and several different trapping sites which hinder tritium diffusion process and releasing behavior. Here we investigate the diffusion mechanisms of tritium and O³H species in LiAlO₂ and Li₂ZrO₃ ceramic pellet in order to understand and quantify the effects on diffusion barriers and diffusion coefficients due to the presence of interstitial and substitutional Li defects, hydroxide (O-³H) vacancy defect, and the interactions of ³H with O-vacancies in Li₂ZrO₃. We find the smallest activation energy barriers of 0.63 and 0.3 eV in LiAlO₂ and Li₂ZrO₃, respectively. The obtained results indicate that the performance of Li₂ZrO₃ could be better than a widely used ceramic in TPBAR, γ-LiAlO₂.