Recovery of hydrogen induced defects and thermal desorption of residual hydrogen in LaNi5

Lattice defects induced by initial hydriding and their effect on residual hydrogen content in LaNi5 have been studied by means of positron lifetime spectroscopy and hydrogen thermal desorption measurement. Component analyses of positron lifetime spectra show that surprising amount of vacancies together with dislocations are generated by the initial hydriding. Vacancy migration in LaNi5 after hydrogen desorption at room temperature is observed around 423-673 K, while dislocations in LaNi5 are much more stable. Hydrogen thermal desorption measurement shows that the release of residual hydrogen occurs mainly in the temperature range from 450 to 650 K, and it ceases at about 800 K. The release temperature of residual hydrogen closely corresponds with the temperature of vacancy migration and annihilation in LaNi5. Residual hydrogen in LaNi5 is most likely trapped by vacancies and vacancy clusters, which are induced by hydriding.