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A novel low-temperature hydride, Mg3MnNi2D3−x with filled Ti2Ni-type structure has been synthesised and its crystal structure has been studied in detail by powder neutron diffraction. Refinement of the structures of β-Mg3MnNi2D1.83 and α-Mg3MnNi2D0.23 deuteride phases showed that D atoms partially fill 16d Mg6 octahedral and 32e Mg3Ni tetrahedral interstices in the cubic metal matrix (sp.gr. View the MathML sourceFd3¯m). The β-hydride was found to be rather unstable, during storage in air it transforms into α-hydride.

The effect of Cu-for-Ni substitution on the structural and hydrogenation properties of the LaCu2 compound with hexagonal AlB2 type structure has been studied. An extended solid solution was found from LaCu2 to La(Cu0.35Ni0.65)2. The La(Cu1−xNix)2 compounds easily absorb hydrogen at room temperature under 1 bar pressure, after preliminary activation treatment by heating in vacuum. Hydrogenation of LaCu2 resulted in the formation of amorphous LaCu2H3.3 hydride. For all Ni-substituted compounds formation of crystalline hydrides with CeCu2 or AlB2 type structure of the metallic sublattice and hydrogen content up to 4.4 at.H/f.u was observed. As found, long-term exposure of the La(Cu0.4Ni0.6)2H4.2 and La(Cu0.35Ni0.65)2H4.0 hydrides to the air or their heating under vacuum up to 100 °C is accompanied by structural transition of the metallic sublattice to Fe2P type structure, previously observed for Pr(Cu,Ni)2-based hydrides.

It is shown that the oxygen-stabilised compounds Zr3Fe(Co)Ox (x = 0–1.0) interact with hydrogen at ambient temperature and pressure forming saturated hydrides with filled Re 3B type structure. The hydrogen storage capacity decreases with increasing oxygen content from 6.7 H/f.u. for Zr3Fe down to 5.35 H/f.u. for Zr3FeO1.0 and from 6.9 H/f.u. for Zr3Co down to 5.3 H/f.u. for Zr3CoO1.0. A small change of the unit cell volumes for the Zr3Fe(Co)Ox parent compounds and a substantial increase of these parameters for the corresponding saturated hydrides were observed with increasing oxygen content. The partial hydrogen-induced lattice expansion, � V/at. H, increases from 2.25 A 3 for Zr3FeH6.7 up to 3.38 A 3 for Zr3FeO1.0H5.35 and from 2.08 A 3 for Zr3CoH6.9 up to 3.25 A 3 for Zr3CoO1.0H5.3. Rietveld refinement using neutron powder diffraction data for Zr 3FeO0.4D6.25 showed a distribution of deuterium atoms and a redistribution of oxygen atoms from octahedral to tetrahedral sites in a similar way as in Zr3NiOxDy. Both 57 Fe Mossbauer spectroscopy and magnetic susceptibility measurements of Fe-containing hydrides indicated weak hydrogen-induced magnetic ordering at low temperatures. The ordering temperatures of Zr3FeO0.2H6.52 and Zr3FeO0.6H6.25 are 105 and 140 K, respectively. © 2004 Elsevier B.V. All rights reserved.