Adsorption characteristics of tritium in lithium vacancy for Li4SiO4: A density functional theory study

Abstract

Lithium orthosilicate (Li₄SiO₄) is a promising breeder material with its high lithium density and low tritium retention for fusion reactor blanket. After neutron irradiation, Li₄SiO₄ not only produces tritium but also forms lithium vacancy defects, which may significantly influence the release and collection of tritium. Therefore, in this paper, the adsorption characteristics of tritium in different lithium vacancy defects of Li₄SiO₄ were systematically studied based on first principles to understand the influence mechanism of lithium vacancies on tritium. Tritium breeder materials are exposed to a flowing mixed-gas atmosphere of helium and hydrogen. In this typical oxygen-poor (O-poor) operational environment, the formation energies were investigated. For comparison, oxygen-rich (O-rich) conditions were also considered. The formation energies, possible adsorption sites and electronic properties of defects were analyzed by constructing lithium vacancy models and tritium adsorption models. It was found that the formation energies of lithium vacancies (V_Li) under O-rich conditions were 1.21–2.16 eV compared with the lithium vacancy-tritium defect complexes (V_Li-T) of 0.52–1.12 eV, which indicates that V_Li-T is easier to form than V_Li under the same conditions. Additionally, the adsorption energies of tritium in V_Li range from −7.021 to −5.581 eV, showing that V_Li has a strong tritium capture ability. Subsequently, by analyzing multiple possible adsorption sites, it was determined that the octahedral V_Li-T configuration, with an average formation energy of 1.24 eV, is more difficult to form. Finally, electronic property analysis suggested that tritium interacts with the 2p orbital of oxygen to form V_Li-T. The study presented in this paper will provide practical guidance for optimizing tritium breeder materials and designing tritium blankets in the future.