EXAFS study of LaNi5 and LaNi4.5Al0.5

We report extended X-ray absorption fine structure measurements in the temperature range between 20 and 300 K at the Ni K absorption edge on LaNi5 and LaNi4.5Al0.5 before and after hydrogen charging. In agreement with previous studies, an increase of the Ni-Ni distance has been found when Ni atoms are partially substituted by Al. For all the samples, the Debye-Waller factors of the Ni-Ni first sub-shells have been fitted with a correlated Debye model plus a temperature independent static disorder, obtaining a Debye temperature dependence on the Al content. Even a small hydrogen content has been found to increase the static contribution to the local disorder around Ni atoms.