3He retention in LaNi5 and Pd tritides: Dependence on stoichiometry, 3He distribution and aging effects

This study compares the He-3 retention properties at room temperature of both LaNi5 and Pd tritides after more than 18 and 13 years, respectively. The effects of stoichiometry have been investigated by following He-3 retention in sub-stoichiometric and stoichiometric samples for both tritides, and in replenished samples for Pd tritide. For both compounds, the change of thermodynamic and structural properties due to 3He retention upon aging time has also been studied by PcT diagrams, X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) measurements. Transmission electron microscopy (TEM) observations were also performed for Pd only. Both LaNi5 and Pd tritides retain more than 95% of He-3 for at least 9 years of aging. However, the influence of 3 He in the matrix has completely different effects since LaNi5 tritide looses its thermodynamic and structural properties after 2.8 years of aging, whereas these properties are outstandingly well preserved in Pd tritide for at least 10 years. This difference has been attributed to a different distribution of 3He atoms, leading to different kind of defects produced by He-3 retention in both materials. (C) 2007 Elsevier B.V. All fights reserved.