Influence of O-related defects introduced by reduction on release behavior of hydrogen isotopes in Li2TiO3

In the operation of deuterium-tritium (D-T) fusion reactors, blanket systems will generate tritium by 6Li (n, α) T and 7Li (n, nα) T reactors in solid tritium breeding materials. Lithium titanate (Li2TiO3) has been considered as one of the promising candidates due to its good tritium release, low activation characteristics and high chemical stability. In order to enhance tritium recovery from the surface of the breeder material, it has been proposed to mix hydrogen into the inert sweep gas. However, Li2TiO3 will be reduced after heating under a reducing atmosphere and generate O-related defects. T. Hoshino et al. reported that masses of the Li2TiO3 samples were found to decrease with time in a hydrogen atmosphere, then to increase after the change of the atmosphere from hydrogen to oxygen. The sample color changed from white to dark blue after heating at 1323 K for 10 h under a reducing atmosphere, 20% H2-Ar. This color change indicated the deficiency of oxygen content confirmed by thermogravimetry, suggesting a change from Ti4+ to Ti3+. Then the color of the sample returned to white by oxidation in O2 gas (Po2 = 1 atm) for 10 h. This was attributed to the movement of oxygen atoms from O2 gas into O-vacancies generated by reduction. In order to control the mass change during of high-temperature use, development of Li2TiO3 which has excess Li2O was studied by T. Hoshino et al.. Li2TiO3 (L100) and Li2.1TiO3.05 (L105) were prepared by solid-state reaction of Li2CO3 and TiO2 powders at 1273 K. In thermogravimetry, the masses of samples L100 and L105 were found to decrease with time in a hydrogen atmosphere which is indicative that something is lost from the sample. However, sample L105 had fewer oxygen defects than L100. K. Tsuchiya et al. developed advanced tritium breeders and good prospects have been obtained by using oxide additives such as TiO2, CaO and Li2O. The order of oxygen defects was confirmed as Ca–Li2TiO3 < Li2TiO3 < Zr–Li2TiO3 < Sc–Li2TiO3. In previous work, O-related defects were considered to be promising defects for trapping tritium and trigger the detrapping and release of tritium.However, there is no report on the influence of O-related defects introduced by reduction on the performance of the tritium breeding blanket. This work is to investigate the influence of these defects on both the release behavior of hydrogen isotopes, and the damage caused by O-related defects in Li2TiO3. The type of O-related defects was also confirmed in this work.