First-principles calculations of LaNi5-xSnxHy intermetallics and intermediate phase

The crystal and electronic structures of LaNi 4:75 Sn 0.25 intermetallics and LaNi 4.5 Sn 0.5 H y ( y =2.0, 2.5) intermediate phase have been investigated by the full-potential linearized augmented plane wave (FP-LAPW) method. Hydrogen occupation sites in LaNi 4.5 Sn 0.5 H y have been determined based on Westlake's criterions: (1) the minimum hole radius is 0.04 nm; (2) the minimum H-H distance is 0.21 nm; as well as geometry optimizations and internal coordinates optimizations. We find that hydrogen atoms prefer to occupy the 12n * , 6m, 12o, 6m * sites in LaNi 4.5 Sn 0.5 H 2.0 and the 6m * , 4h, 6m, 12o, 12n * sites in LaNi 4.5 Sn 0.5 H 2.5 . The specific coordinates of hydrogen atoms in LaNi 4.5 Sn 0.5 H y are also determined. The results show that hydrogen atoms tend to keep away from tin atoms. The maximum hydrogen content decreases compared with LaNi 5 . The interactions between Sn and Ni with H play a dominate role in the stability of LaNi 4.5 Sn 0.5 -H system. Lattice expansion and increment of Fermi energy E F show that both Sn and H atoms decrease structural stability of these alloys.