The observation of the lattice defect formation during the hydrogenation and dehydrogenation in La(Ni,Sn)₅ by in-situ positron lifetime measurement

To clarify the effect of Sn substitution for Ni of LaNi₅ on the lattice defect formation during the hydrogenation and dehydrogenation processes, in-situ positron lifetime measurements were performed in LaNi _4.93Sn_0.27. During the hydrogenation, the mean positron lifetime, τ_m, monotonically increased up to 175 ps which is almost same as calculated positron lifetime for vacancy. This shows vacancy introduction by hydrogenation. The τ_m decreased down to 135 ps with hydrogen content during the dehydrogenation. It shows that the vacancies are removed from the lattice during the dehydrogenation. These results show that vacancies in LaNi_4.93Sn_0.27 are introduced and removed reversibly during the hydrogenation and dehydrogenation. The concentrations of vacancy and dislocation were 1 × 10^-5 and 6 × 10⁹ cm^-2, respectively. These values are two orders lower than those in LaNi₅.