First-principles study of structures, electronic and elastic properties of LaNi_5-xFe_x(x: 0.25-1.25)

The structural, electronic and elastic properties of LaNi_5-xFe_x (x = 0.25, 0.5, 0.75, 1, 1.25) have been investigated employing the density functional theory with the generalized gradient approximation (GGA). The optimized results indicate that Fe prefers to substitute Ni atom in the 3 g site, and Fe replaces 2c site of Ni atom up to x = 1.25. The radius of 6 m interstitial site gradually increases as x goes from 0 to 1.25 due to volume expansion, which is one of the reasons for the increase of hydrogen storage. Combined with elastic constants and elastic modulus, the anti-pulverization ability of the La-Ni-Fe system enhances, and LaNi_4.25Fe_0.75 has the best anti-pulverization capability among six crystal structures. According to the density of states, the new peak appears at near -5 eV which is dominated by Fe-3d States. Based on the analysis of charge distributions and charge density differences, the sequence of interaction between atoms is Ni_2c-Fe_3g > Ni_2c-Ni_3g > Ni_3g-Ni_3g > Ni_3g-Fe_3g > La-Ni_2c > La-Fe_2c, while that of the interactions with H atom is as follows: Fe > Ni_3g > Ni_2c > La. The electron hybridization of H and La, Ni, Fe atoms form covalent bonds through electron transfer.