First-principles electronic structure calculations were performed in order to investigate vacancy formation in LaNi5. The Ni dumb-bells at La sites accommodate the excess Ni atoms removed as Ni vacancies. Clear site dependence was observed in vacancy formation energies: the formation energy of the Ni vacancy at the 2c site was about 0.8eV lower than that at the 3g site. The formation of Ni vacancies at the 2c sites led to the decrease of the lattice parameter a and the increase of the lattice parameter c. This trend exhibited good agreement with the change in lattice parameters by activation of LaNi5. The calculated results indicated that Ni vacancies were mainly formed at the 2c sites in the hydrogen absorption–desorption process in LaNi5.

First-Principles Study of Vacancy Formation in LaNi5. M.Mizuno, H.Araki, Y.Shirai: Journal of Physics - Condensed Matter, 2008, 20[27], 275232 (5pp)