Ab initio study of helium behavior in titanium tritides

Ab initio calculations based on density functional theory have been performed to investigate the relative stability of titanium tritides and the helium behavior in stable titanium tritides. The results show that the β-phase TiT1.5 without two tritium along the [1 0 0] direction (TiT1.5[100]) is more stable than other possible structures. The stability of titanium tritides decrease with the increased generation of helium in TiT1.5[100]. In addition, helium generated by tritium decay prefers locating at a tetrahedral site, and favorably migrates between two neighbor vacant tetrahedral sites through an intermediate octahedral site in titanium tritides, with a migration energy of 0.23 eV. Furthermore, helium is easily accumulated on a (1 0 0) plane in β-phase TiT1.5[100].

• The β-phase TiT1.5 without two tritium along [1 0 0] direction is the most stable.
• The stability of titanium tritides decreases with the increasing of helium.
• Helium generated by tritium decay prefers to occupy at a tetrahedral site.
• Helium favorably migrates between two nearest vacant tetr. sites via an octa. site.
• Helium is easily accumulated on a (1 0 0) plane in β-phase TiT1.5[100].