First Principles Study of Tritium Diffusion in Li2TiO3 Crystal with Lithium Vacancy

Li2TiO3 is one of the most significant breeder materials and has potential applications in future fusion reactors. Defect models with three types of lithium vacancies were considered to study the diffusion behavior of tritium in Li2TiO3 by the density functional theory calculations. The possible tritium adsorption sites inside the lithium vacancy were examined and analyzed. The energy barrier of all diffusion paths between different adsorption sites was calculated and the minimum energy barrier is about 0.45 eV, which indicates that the tritium atom diffuses freely inside the lithium vacancy; when a tritium diffuses across the crystal in the typical three directions, our results reveal that the tritium atom prefers to move along the [010] direction. Furthermore, we found that the minimum energy barrier for the tritium atom to escape the trap of Li vacancy is 0.76 eV. After the tritium jumping out of the Li vacancy, the minimum energy barrier is 0.5 eV for the tritium atom diffusing in the crystal. Therefore, we predict that tritium can easily escape from the trap of the Li vacancy and then diffuse across the crystal. Such results are beneficial to the tritium release process in Li2TiO3 and could provide theoretical guidance for the future applications of the Li2TiO3 materials.

Tritium adsorption in the lithium vacancy of Li2ZrO3: A first principles study

Tritium adsorption in the irradiation defects of the Li2ZrO3 is a fundamental problem to understand the tritium behavior during the release process. A comprehensive computational study of tritium/helium adsorption in the lithium vacancy of bulk Li2ZrO3 is presented by the density functional theory calculations. The most stable tritium adsorption position has been found and it is determined by the neighboring lithium–oxygen interactions. The results reveal that the intrinsic defect is the lithium vacancy with one electron and it transforms to be the neutral state after a tritium atom is adsorbed. Moreover, helium is adsorbed almost in the center of lithium vacancy without bonding with surrounding oxygen atoms, which could diffuse easily in the bulk Li2ZrO3. Therefore, we predict that the intrinsic Li vacancy tends to adsorb a positive ion T[Formula: see text] other than a neutral T atom. Our results provide theoretical support to understand the T behavior in the Li2ZrO3 crystal.