X-ray diffraction peak broadening and lattice strain in LaNi5-based alloys

Peak broadening in X-ray powder diffraction (XRD) profiles of LaNi5-based a lloys after hydriding and dehydriding processes was investigated in order t o clarify the mechanism of formation of lattice strain in hydriding and deh ydriding. The Rietveld method was used to evaluate the degree of peak broad ening and to determine anisotropic peak broadening axis for LaNi5 and LaNi5 - aMa (M: Mn, Fe, Cu, Al; alpha=0.25, 0.5) before hydriding, after activat ion and after 1000 hydriding-dehydriding cycles. All the alloys studied sho wed anisotropic broadening vectors of the same direction (110) after activa tion. The degree of the peak broadening, however, strongly depended on the substitution elements. Hydriding-dehydriding cycles did not influence the d irection of the anisotropic peak broadening axis, while both anisotropic an d isotropic peak broadening increased with number of cycles. It was found t hat the lattice strain analyzed from the peak broadening in X-ray diffracti on profiles corresponded to dislocations with Burgers vectors (hk0) observe d by transmission electron microscope. (C) 2000 Elsevier Science S.A. All r ights reserved.