HYDROGEN EFFECTS ON THE ELECTRONIC AND MICROSTRUCTURAL PROPERTIES OF CE, NI, AND CENI2 INTERMETALLIC COMPOUND

The electronic properties and the microstructure associated with room temperature (RT) cathodic charging of Ce, Ni, and CeNi2 massive specim ens have been investigated by XPS analysis and microscopic observation s. The use of a cooling stage allows us to study the hydride formed by cathodic charging on the nickel surface and to evidence by XPS the hy drogen induced filling of the 3d band in nickel. A thin hydride layer (CeH2.53) is readily formed at RT on Ce. In spite of a hydrogen induce d lowering of the valence band intensity, conduction states at E(F) ar e present in this hydride. The XPS spectra of the Ce 3d and 4d core le vels also demonstrate the existence of a hybridization effect of the 4 f electrons with those of the conduction band which raises the intensi ty of the f0 and f2 satellites. Needle-shaped hydride precipitates are observed at the very beginning stage of the cathodic charging of CeNi 2; they are readily replaced by an amorphous CeNi2H4 hydride. The hydr ogenated surface exhibits a metal-hydrogen band at 6 eV below E(F); th e presence of hydrogen also increases the relative intensity of the f0 and f2 satellites in the 3d and 4d core levels.