Defects Formation in LaNi₅-based Alloys Investigated by In-situ X-ray Diffraction

Defects formation in LaNis-based alloys was investigated by X-ray diffraction (XRD). In-situ XRD data measured along the first hydriding-dehydriding P-C isotherms were analyzed by the Rietveld method. Lattice strain and crystallite size were evaluated from the peak profile. In LaNi₅ hydride phase formed accompanying with 2 % of anisotropic lattice strain in <hk0> direction caused by dense dislocations. Coexisting solid solution phase was not affected by the strain in the hydride phase. Lattice parameter a became smaller after cycles than before hydriding, which is related with vacancies formation. Only 5 % of Al substitution for Ni dramatically changed the defects formation behavior. Hydride phase did not show lattice strain in the first hydriding but showed small strain during dehydriding. Formation of both dislocations and vacancies are strongly affected by substitution of other elements for a part of Ni.