The relationship between microstructure and H absorption-desorption was investigated as a function of the number of H sorption cycles. The desorption pressure did not depend significantly upon the number of cycles, but the absorption pressure decreased as the number of cycles increased; with the most significant decrease occurring between the first and second cycles. Transmission electron microscopy revealed that numerous a-type edge dislocations were introduced during the first absorption cycles. The introduction of numerous lattice defects (such as a-type edge dislocations), as well as the formation of severe cracks, was responsible for a significant decrease in the absorption pressure between the first and second cycles. This indicated that reproducible pressure-composition characteristics could be achieved only when numerous dislocations and cracks were formed in the bulk of LaNi5 particles

Effects of Lattice Defects on Hydrogen Absorption-Desorption Pressures in LaNi5. T.Yamamoto, H.Inui, M.Yamaguchi: Materials Science and Engineering A, 2002, 329-331, 367-71