Alloying effects on the electronic structures of LaNi 5 containing hydrogen atoms

Abstract

The electronic structures of LaNi5 intermetallic compounds containing a variety of alloying elements were investigated by the DV-Xα cluster method in order to understand the effects of alloying on the hydrogen absorption and desorption characteristics of these compounds. It was found that hydrogen atom made a stronger chemical bond with Ni atoms than with La atoms in pure LaNi5. The bond strengths between hydrogen and Ni (or La) atoms were scarcely influenced by alloying, despite the fact that hydriding and dehydriding characteristics are greatly modified by the addition of alloying elements. On the contrary, both the Ni−Ni and the La−Ni atomic interactions were greatly affected by alloying. It was shown that the ratio of the La-Ni bond order to the Ni−Ni bond order correlated well with experimental data of dissociation pressures. This correlation was also found in other compounds, YNi5 and CaNi5. It was concluded that the strengths of the chemical bonds between the constituent atoms determined the essential features of the hydrogen absorption and desorption characteristics of the ANi5-type intermetallic compounds.