Positional disorder in LaNi5-ySny intermetallic phases

There has been extensive research on the LaNi5-ySny intermetallic phases because of their unique hydriding properties. Current research involves studies of the location of the Sn substituent in the phase, the substituent being important in alleviating thermal degradation of the phases during hydriding-dehydriding cycles. Experiments to date, however, have not examined positional disorder in the LaNi5-ySny phases. The principles of the P6/mmm structure are certainly correct, but preliminary single-crystal studies suggest that disorder of the atoms in the phases may occur to alleviate short interatomic distances in the compounds, in particular the short La-Ni(c) distances which are 0.2 Angstrom less than the sum of the atomic radii in the putative ordered P6/mmm atomic arrangement. High precision single-crystal diffraction studies, using sphere-ground crystals, are currently underway to investigate such disorder. Copyright (C) 1997 International Association for Hydrogen Energy.