In situ XAS study of the hydrogenation of AB 5 compounds (A=La, Ce and B=Ni 3.55Mn 0.4Al 0.3Co 0.75)

Abstract

The XAS spectra of La 1− x Ce x B 5 (B=Ni 3.55Mn 0.4Al 0.3Co 0.75; x=0, 0.5, 1) at the Ce L III and transition metal K edges have been measured in situ upon hydrogen absorption. The evolution of the Ce valence from an intermediate valent state to a trivalent state as the hydrogen content increases leads to an increase of Ce radius, which rules the structural and thermodynamic properties of the hydrides. The decrease of the prepeak intensities of the transition metal K edges, is related to the change of the density of states upon hydrogen absorption. The presence of cerium modify also the filling of the 3d band, and shift the formation of a stable hydride to larger H content.