Lattice defects introduced during hydrogen absorption-desorption cycles and their effects on P-C characteristics in some intermetallic compounds

The generation of lattice defects and their effects on hydrogen sorption properties described in terms of pressure-composition (P-C) isotherms have been investigated as a function of the number of hydrogen sorption cycles for LaNi5 and FeTi. For LaTi5, while the desorption pressure does not significantly depend on the number of cycles, the absorption pressure drastically decreases between the first and second cycles. Numerous dislocations of edge character with Burgers vectors of the 1/3 (1210)-type as well as numerous cracks are introduced during the first absorption cycle. The introduction of numerous lattice defects such as a-type edge dislocations and the formation of severe cracks seems to be completed during the first cycle, resulting in the reproducible P-C characteristics for the subsequent cycles. In contrast, FeTi exhibits ever-changing P-C characteristics with cycle number. The introduction of dislocations and cracks occurs during each of the absorption cycles. However, the extent to which this occurs is considerably smaller in each absorption cycle of FeTi than in the first absorption cycle of LaNi5. The difference in material response to hydrogenation seems to be closely related to the difference in ductility of these two intermetallics. (C) 2002 Elsevier Science B.V. All rights reserved.