First principles investigation of the substitutional doping of rare-earth elements and Co in La4MgNi19 phase

Abstract

RE-Mg-Ni alloys, including AB3, A2B7, A5B19 and AB4 types, have received extensive attention due to their excellent hydrogen storage properties. La4MgNi19 is the one of the outstanding candidate for hydrogen storage. In this work, the structure, phase stability and electronic structure of the different La-site partial substituted by Pr, Sm, Gd, Nd and NI-site substituted by Co have been investigated by means of the density functional theory.The calculation results show that La4MgNi19 alloy shows the negative enthalpy of formation, indicating the more stable in the thermodynamic. When the substitution of La occurs, among the two sites La(2c) and La(4f), Pr, Nd, Sm and Gd preferentially occupy the La(4f) site. And the addition of the four doping elements will reduce the stability of the phase. Among them, Pr substituted La4MgNi19 has the highest structural stability. When Co substituting Ni, a single Co atom occupies the Ni(12k) preferentially among the seven different Ni positions. During this process, the crystal structure will be destabilized. The DOS results show that the system still puts up the metallic character after substitution. Sm(La(4f)) has the maximum valence band width. The stability of four doped alloys from high to low is: Pr, Nd, Sm, Gd, which is consistent with the enthalpy of formation results. The enthalpy of formation of hydrides shows that, the bounding hydrogen capacity of the system can be obtained as Nb > Sm > Pr > Gd.