Preparation of highly overstoichiometric LaNi5+x (1 <= x <= 4) single-phase films by ion beam sputtering

Single-phase LaNi6.1 and LaNi9.2 films with hexagonal TbCu7 structure have been successfully obtained. Films in the micron scale range were deposited by ion beam sputtering on sapphire and glass substrates heated at 600 K. A two-material La-Ni mosaic target was used for this purpose. X-ray diffracti on and transmission electron microscopy investigations show that the lattic e parameters of the hexagonal structure follow a linear dependence for Ni c oncentration. This result relates to a random substitution of La atoms for Ni dumbbell pairs in the ordered CaCu5 structure. The films exhibit a stron g preferential orientation, with the c axis parallel to the substrate plane , which seems to be favored by the presence of Ni dumbbell pairs. The expec ted impact of this phase on the preparation of new hydrogen storage materia ls is discussed. (C) 1999 American Institute of Physics. [S0021-8979(99)050 24-0].