The defects energetics of the γ-LiAlO2, Li2TiO3, and Li2ZrO3 materials are investigated based on density functional theory (DFT) calculations for the tritium-producing burnable absorber rod (TPBAR) materials used in nuclear reactors. Analysis of charged defects including vacancies, interstitials, antisite defects, and 3H substitutional defects was performed using ab initio thermodynamic methods to identify the trends of the point defect stability under the TPBAR operating temperature and the relevant P(O2) conditions. Interactions between the point defects and the 3H species were also examined by looking into the formation energy differences between the 3H related defect products and their corresponding reactants as a functional of electron chemical potential across the band gap. Our results suggest that the experimental tritium/hydrogen diffusivities, with the diffusivities in γ-LiAlO2 being the slowest (Li2TiO3 &gt; Li2ZrO3 &gt; γ-LiAlO2), correlate with the defect formation energy trends calculated theoretically. The defect formation energies were found to be higher in γ-LiAlO2 than in the other two materials, leading to lower tritium transport carrier concentration. The higher point defect formation energies indicate a greater stability of γ-LiAlO2 and the possibility to better withstand the long-term irradiation at high temperatures in the reactor. Furthermore, the strong interactions up to about -2.5 eV between the 3H interstitial and the VLi, VO, and Oint defects in γ-LiAlO2 phase might be responsible for trapping of 3H species at bulk point defects, which reduces the efficiency of tritium recovery in the TPBARs.

Density functional theory study of the point defect properties of γ-LiAlO2, Li2ZrO3, and Li2TiO3 materials

256th National Meeting (2018)

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