Tritium trapping by oxygen and lithium vacancies in Li4TiO4 from first-principles calculations

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The Li4TiO4 ceramic is a promising solid-state tritium breeder material for the production of tritium fuel in the designs of fusion reactors. Tritium extraction efficiency is one of the key factors that determines the performance of the breeder material. Vacancies are known to trap tritium and adversely affect tritium extraction. Understandings of tritium-trapped defect configurations in Li4TiO4 are limited so far. In this work, the oxygen/lithium vacancy (VO/Li) and the vacancy-tritium defect complex (VO/Li + T) in Li4TiO4 are studied by first-principles density functional theory. The atomic configurations, formation energies and electronic structures of various charged defect species are obtained. We find that 2+ and 0 are the dominate charge states of VO, 1- is the dominate charge state of VLi, 1+ is the dominate charge state of the defect complex (VO + T), and 0 is the dominate charge state of (VLi + T). Tritium atoms trapped in VO are bonded to Ti atoms, and those trapped in VLi are bonded to O atoms.