First-principles study of the surface properties of γ-LiAlO2: Stability and tritium adsorption

• Published in: Journal of nuclear materials 2019-08, Vol.522 (C), p.1-10
• Main Authors: Jia, Ting, Zeng, Zhi, Paudel, Hari, Senor, David J., Duan, Yuhua
• Format: Article
• Language: English
• Subjects: Adsorption; Charge transfer; Density functional theory; First principles; Mathematical analysis; Neutron radiation; Nuclear energy; Oxidation; Pressurized water reactors; Rods; Stability of γ-LiAlO2 surface; Surface chemistry; Surface properties; Surface stability; Tritium; Tritium adsorption and diffusion; Tritium-producing burnable absorber rod (TPBAR) materials; Unit cell
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2019.05.007

γ-LiAlO2 enriched with 6Li isotope exhibits excellent performance under neutron radiation and is used in tritium-producing burnable absorber rods (TPBARs) to produce tritium (T, 3H) in pressurized water reactor (PWR). To better understand the 3H formation and diffusion on the surfaces, the first-principles calculations are performed to study the stability of γ-LiAlO2 surface and the 3H adsorption on the surface. By considering all possible symmetrical stoichiometric and nonstoichiometric low-index surfaces, two most stable surfaces, one stoichiometric (100) and one nonstoichiometric (101), were identified. The 3H adsorption and diffusion on the most stable (100) surface were further explored, and the obtained results show that there are four stable sites (three O and one Al atop) for 3H adsorption. The calculated Bader charges of atoms reflect that 3H adsorption on the top of O site is a reduction process, while on the top of Al site is an oxidation one. Under low adsorption coverage of 1/4 per surface unit cell, 3H atoms are adsorbed on the most stable OA atop site. With increasing 3H diffused from bulk to surface, the AlG site is the second choice for 3H adsorption, and then the OB site. The coverage of 2/4 is the most favorable 3H adsorption state due to the counteracted charge transfer. When the coverage is up to 4/4, the interaction between 3H atoms leads to partial formation of T2 molecule that desorbs from surface. Therefore, T2 molecule should be the main product from the perfect surface of γ-LiAlO2 at high 3H coverage. [Display omitted] •The most stable low-index surfaces of one stoichiometric (100) and one nonstoichiometric (101) were identified for γ-LiAlO2.•There are four stable sites (three O and one Al atop) for 3H adsorption on the most stable (100) surface.•With increasing its coverage, the 3H atoms first adsorb on the most stable OA atop site, then the AlG and OB sites.•The 2/4 coverage with one O atop site and one Al atop site is the most favorable 3H adsorption state.•When the coverage is up to 4/4, the 3H atoms partially combine to T2 molecule and then desorb from surface.