Nano scale structure such as nano-size crystallites and defects can be found in conventional hydrogen absorbing alloys

Our progress on crystal structural studies on hydrogen absorbing alloys including intermetallics and solid solutions is reviewed. LaNi5 shows an extremely high equilibrium pressure at the first hydrogen absorption but not at the second one. The structural change in the first absorption was followed by in-situ X-ray diffraction (XRD). We found that the crystalline size did not change but the anistropic strain was introduced to the lattice of the hydride formed. The strain introduced was not relaxed in the following dehydrogenation and hydrogenation. However, the behavior of LaNi4.75Al0.25 for the first absorption was completely different from LaNi5. The stain observed for LaNi5 was not found at the first absorption but reversible stain parallel to c-axis was observed in desorption.