"Physical properties and electronic structure of LaNi5 compound before and after hydrogenation: An experimental and theoretical approach"

Abstract

The present study deals with the experimental and theoretical approaches of LaNi5 hydrogen storage alloy. The structural, morphological and hydrogenation characterization of this sample which is synthesized by the arc melting technique were carried out by X-ray diffraction, scanning electron microscopy and a homemade Sievert's type apparatus, respectively. The results showed that after several hydrogenation/dehydrogenation cycles, disproportionation occur in LaNi5. The hydriding kinetic measurements under different applied pressure show that the hydrogen storage capacity (Cwt.%) increases with pressure. However, kinetic analysis at different temperatures under constant initial pressure, which is fitted to two models such as Jander diffusion model and Johnson-Mehl-Avarmi, revealed that Cwt.% and hydriding reaction rate are decreased and increased by increasing of temperature, respectively. The theoretical study using full potential linearized augmented plane wave plus local orbitals method was also performed to investigate the structural, energetic and electronic properties of LaNi5 and its saturated hydride (LaNi5H7). From the two possible space groups for LaNi5H7, P63mc was found as the most favorable one. A volume expansion of ~%26 was found for its hydride. Other calculated results including the equilibrium atomic positions, bulk modulus and the enthalpy of formation were in good agreement with other theoretical and experimental results. The band structure calculations showed that the valence bands were mainly derived from Ni-3d states, and the bandwidth of the occupied Ni-3d bands in hydride phase was narrower than that of the parent compound due to the filling of Ni-3d bands as a result of hydrogen absorption and volume expansion.