Phase stability and bonding characteristics of Li-rich Al-Li intermetallic compounds: Al2Li3 and Al4Li9

The all-electron local-density full-potential linearized augmented-plane-wave method was applied to calculate the total energy and electronic structure of several Li-rich Al-Li compounds including Al2Li3, Al4Li9, and AlLi3 (with L12 and D03 structure). The ground-state properties are found to be in good agreement with the available experimental data. Based on the calculated heats of formation, both Al2Li3 and Al4Li9 were found to be stable, whereas both AlLi3 compounds are unstable with respect to the mixture of the most stable compounds. The bonding in the stable phases is characterized by its tendency to form stronger, tetrahedra-like Al-Al bonds due to the Al-Al and Al-Li interactions. Based on these results, we propose that the phase stability and the bonding characteristics of the Al-Li alloys can be understood by assuming that the Li atoms basically transfer their valence electrons in between the Al bonds and that the resultant strengthened Al bonds stabilize the Al-Li compounds.