Hydrogen sites occupation in α-LaNi₄Al hydride

Abstract

The hydrogen sites occupation in La₂Ni₈Al₂H has been investigated by a first-principle calculation to study the effect of the Al atom on the location of hydrogen and to explore the dominating factors to determine the hydrogen sites. It is found that the hydrogen cannot be stationed at interstitial sites surrounded by atoms including Al. Judged from the solution energy of hydrogen, the 12n site is most stable and the 4h site cannot accommodate H. The hydrogen occupation in LaNi₄Al shows a distinct way from that in LaNi₅, where five nonequivalent interstices (3f, 4h, 6m, 12o, 12n) have been reported to be available for the hydrogen in LaNi₅. This indicates that the Al atom has important influence on the hydrogen occupation. The seems to be a parameter to measure the stability of La₂Ni₈Al₂H. By analyzing the density of states combined with the local environment of sites, the bond order (BO) and average Mulliken charge (AMC), we found that the 12n and 3f sites have similar atomic and electronic structure and the covalence and ionicity. The 3f site is also favorite occupation for hydrogen besides the 12n site.

Keywords:

• Hydrogen occupation
• First-principles calculation
• La₂Ni₈Al₂H
• Electronic structure
• Covalence
• Ionicity

Acknowledgements

The authors are grateful to Dr D.S. Xu, department of Titanium Alloys, Shenyang advanced material R&D center, at this laboratory for computer resources and helpful discussions.