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The equiatomic RTX intermetallic compounds ( R = rare earth metal ; T = Fe , Co , Ni ; X = non-transition element ) exhibit interesting crystal structures, hydrogenation and magnetic properties. The hexagonal intermetallics are frequently formed in these systems and can be obtained via internal and external deformation of the AlB2-type metal sublattice accompanied by a partial substitution of T by X. This work was focused on studies of hydrogen interaction with LaCuSn and CeCuSn intermetallics. Original compounds crystallise with the hexagonal “a *2c” type structures characterised by ordering of Cu and Sn with a slight internal deformation. ( c / a ) hex was found to be significantly higher for R = La . The structural phase transformations were studied by synchrotron XRD and powder neutron diffraction. The hydrogenation is accompanied by a small volume expansion (0.8–1.1%) proceeding exclusively along [0 0 1] and leading to a rebuilding of the structures of (La,Ce)CuSnD0.3–0.5 into deformed AlB2 type (Cu + Sn disordered; “a *c” cells). Deuterium atoms partially occupy trigonal bipyramidal R3Sn2 sites with D slightly shifted from the R3 planes towards the R3Sn tetrahedra. Thermal desorption properties studied by the vacuum TDS technique show that D desorption leads to a reversible formation of the initial intermetallics that restores the LiGaGe (Cu + Sn ordered) type structure.

Phase-structural transformations during hydride formation and decomposition in the advanced hydrogen storage alloy LaNi4.7Sn0.3, are studied by in situ synchrotron X-ray powder diffraction (SR-XRD). A specially designed cell for in situ studies in H2-atmosphere is attached to a metal hydride hydrogen storage unit developed at IFE providing hydrogen gas at convenient pressures. The studied sample is kept in a quartz glass capillary. Temperature cycling between RT and 100 ° C at H2 pressures of 2–3 bar was employed to LaNi4.70Sn0.30H°∼6 which resulted in a reversible hydrogen absorption–desorption process. Both a large temperature-dependent homogeneity range of the β -hydride and a small hysteresis in the formation-decomposition of the β -hydride have been revealed.

The influence of O 2 and H 2 O on the hydrogen reactivity with the surface of LaNi 4.7 Sn 0.3 was studied at 298 K by a volumetric Wagener method. A significant enhancement of the H 2 reactivity by precovering the surface by both O 2 and H 2 O was observed. A formation of the oxygen deficient SnO 2− x in the surface layer acting as a catalyser of the H 2 dissociation stands as possible reason for such an improvement. The present data explain the reasons for the improvement of hydrogen cycling properties by the Sn-doped LaNi 5 alloys.

The rate of hydrogen desorption in the LaNi 4.7 Sn 0.3 -H system studied by means of the volumetric technique has been found to be controlled by H diffusion. Apparent diffusivities of H were estimated using the spherical model and showed a decrease of D on a transition from the α-solid solution to the β-hydride region (6.7 × 10 −10 cm 2 /s for LaNi 4.7 Sn 0.3 H 3.2−5.3 and 1.2 × 10 −9 cm 2 /s for LaNi 4.7 Sn 0.3 H 0.2−0.5 at 298 K). Apparent diffusivity for 3.0 4.7 Sn 0.3 ] 4.7 Sn 0.3 ]

Unusual intermetallic deuteride LaNiInD 1.63-x containing D...D pairs with very short D...D separations of 1.63 A has been studied at 200K at pressures up to 40 GPa by high-pressure synchrotron X-ray diffraction. In the elastic region (