Substitution Effect of Rare Earth on Hydrogenation for AB₅-Type Alloys

Abstract

Substitution effects of rare earth elements for hydrogenation of MmNi_3.55Co_0.75Al_0.30Mn_0.40 AB₅-type alloys were investigated, where Mm consisted of La-Pr-Nd-M (M : Ce, Y, Gd, Tm and Lu), and the amount of La and M was adjusted to keep the lattice volume identical which leads to a similar equilibrium hydrogen pressure. The above alloys showed two-phase reaction during hydrogenation, and both the phases had the orthorhombic lattice with a space group of Cmmm after activation. The Ce containing alloy showed a higher equilibrium hydrogen pressure (0.12 MPa) than the others (0.07–0.10 MPa) at 298 K. In addition, this alloy showed the largest lattice volume expansion among the alloys investigated. However, lattice strain of the hydride phases calculated from line broadening in X-ray diffraction peaks showed to be less than 0.9% for all the alloys investigated.