In situ synchrotron powder diffraction data for the LaNi5–H system were collected, and the dislocation structures formed during the H activation cycle, were studied by using Rietveld refinement analysis in which anisotropic line-broadening was modelled by dislocation scattering. Marginal line broadening was observed in the α phase formed by the very first H absorption by virgin metal. It could best be modelled by a/3<¯21•0>

dislocations, on basal {00•1} slip planes, at densities of 1010 to 1011/cm2. On the other hand, in the β-phase (LaNi5H6) and the activated α-phase (LaNi5H0.4 post-desorption) most dislocations were prismatic, with a {0¯1•0} slip plane and the same Burgers vector; with only a small proportion (15%) of dislocations having basal slip planes. High dislocation densities, of the order of 1012/cm2, were associated with distributed strain fields of intermediate range. The results supported the idea that the dislocation structure was inherited during the α-β phase transition; with dislocations from the first-formed α-phase on basal planes, and the majority being created during nucleation and growth of the β-phase on the prismatic planes. All of these were retained during subsequent phase transitions.

Synchrotron Powder Diffraction Line Broadening Analysis of Dislocations in LaNi5-H. E.Wu, E.M.Gray, D.J.Cookson: Journal of Alloys and Compounds, 2002, 330-332, 229-33