Anisotropic Diffusion of a Charged Tritium Interstitial in Li2TiO3 from First-Principles Calculations

Tritium diffusion in the nuclear fusion reactor breeder material Li2TiO3 is a fundamentally important process for tritium-release kinetics. The energy barrier of tritium diffusion in Li2TiO3 has been reported with a considerable uncertainty in previous experiments. Here, we perform systematic density-functionaltheory (DFT) studies for the diffusion processes of positively charged tritium, which is the preferential charge state of the tritium interstitial in a single Li2TiO3 crystal. By calculating various local-diffusion minimum-energy paths, we find that the diffusion of tritium is strongly anisotropic along different crystalline directions. The most favorable diffusion paths appear within a Li-6 atomic single layer of Li2TiO3 and the corresponding DFT diffusion barrier is 0.334 eV, while the diffusion barrier for the most favorable diffusion paths crossing a Li2Ti4 atomic layer is 1.006 eV.