Distributions of hydrogen and strains in LaNi5 and LaNi4.75Sn0.25

Hydrogen distributions and internal strains that accompany hydriding of binary LaNi5 were compared to those of the ternary alloy LaNi47.5Sn0.25, which is known to have a cycle life superior to that of LaNi5 in electrochemical cells and in gas storage applications. X-ray diffractometry shows that the unit cell volume of the hydride phase changes more continuously with hydrogen concentration in LaNi4.75Sn0.25 than in binary LaNi5. Gas-phase isotherms show that the Sit atoms make significant changes to the local chemical potential of hydrogen atoms. Using generic hydrogen-solute interactions in Monte Carlo simulations and physical arguments, it is shown that normal coarsening of hydride zones will be altered, or even arrested, by hydrogen-solute interactions. Small-angle neutron scattering shows that the distribution of deuterium in partially-deuterated LaNi4.75Sn0.25 is more homogeneous than, in partially-deuterated LaNi5, at least on the spatial scales around 100 Angstrom. It is suggested that the more homogeneous deuterium distribution in LaNi4.75Sn0.25 suppresses the strain gradients that cause decrepitation of the metal hydride. (C) 2002 Elsevier Science B.V. All rights reserved.