First-principles study of vacancy formation in LaNi5

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