Strain formation and lattice parameter change in LaNi_4.75Sn _0.25-H system during the initial activation process

Hydriding-dehydriding behavior of LaNi_4.75Sn_0.25 was investigated by means of in situ X-ray diffraction (XRD). Lattice strain formed only in the hydride phase during dehydriding in the two-phase region. Isotropic strain increased up to 1.7% with decreasing fraction of hydride phase accompanied with anisotropic strain of ∼0.7%. Significant lattice parameter change was observed in the hydride phase both in the single-phase and two-phase regions only in dehydriding but not in hydriding. Both lattice parameters a and c for the hydride phase decreased by about 0.005nm over the two-phase region. The behavior of LaNi_4.75Sn_0.25 in lattice parameter change and lattice strain formation during hydriding-dehydriding are quite different from those observed in LaNi₅ but are similar to those seen in LaNi_4.75Al_0.25.