First-principles study of the surface properties of LiAl5O8 : Stability and tritiated water formation

[摘要] LiAl5O8 is an important secondary phase of gamma-LiAlO2 ceramics in tritium (H-3, T)-producing burnable absorber rods (TPBARs), present in small quantities in the as-fabricated condition and in larger quantities after irradiation due to Li burnup and mobility in the radiation-damaged lattice. In this work, we performed first-principles calculations to study the stabilities and structures of LiAl5O8 surfaces the possibility of T2O formation on the (111) surface. By calculating the surface energies of all possible symmetrical stoichiometric and nonstoichiometric low-index surfaces, we identified the two most stable surfaces, one stoichiometric (001) surface and one nonstoichiometric (111) surface in an O-rich condition. The surface oxygen atoms on the nonstoichiometric (111) surface have remarkable displacements after relaxation, due to the large dangling O bonds. Considering a Li-poor and (3) H-rich condition relevant to TPBARs, we further studied these two stable surfaces with 37.5%, 75%, and 100% surface O atoms covered by H-3 atoms. Our results show that the H-3 saturation is favorable for the nonstoichiometric (111) surface but not for the stoichiometric (001) surface. In addition, the structure of nonstoichiometric (111) surface is well stabilized when the surface O atoms are 100% saturated by H-3 atoms. Based on the fully H-3-saturated (111) surface, the (H2O)-H-3 desorption with an energy barrier of 0.69 eV is preferable in the H-3-rich condition. (C) 2021 Elsevier B.V. All rights reserved.

[发布日期] 2021-11-01

[关键词] LiAl5O8 surfaces;Tritium-producing burnable absorber rods (TPBARs);Density functional theory;Tritium Saturation and (H2O)-H-3 formation