Hydrogenation of oxygen-stabilized Zr3NiOx compounds

It is shown that oxygen-stabilized compounds Zr₃NiO_x (x=0.4, 0.6, 0.8, 1.0) interact with hydrogen at ambient temperature and pressure forming saturated hydrides with a filled Re₃B-type structure. The hydrogen storage capacity decreases with increasing oxygen content from 6.65 H/f.u. for Zr₃NiO_0.4 down to 5.58 H/f.u. for Zr₃NiO_1.0. A slight decrease of the crystal lattice parameters of the parent compounds and a substantial increase of these parameters for the saturated hydrides were observed with increasing oxygen content. The partial hydrogen-induced lattice expansion, ΔV/at. H, increases from 2.333 ų for Zr₃NiO_0.4H_6.65 to 3.047 ų for Zr₃NiO_1.0H_5.58. Joint Rietveld refinement using X-ray and neutron powder diffraction data showed a distribution of deuterium atoms on similar positions as in oxygen-free Zr₃FeD_x and Zr₃CoD_x. The oxygen atoms move during deuteration from the octahedral site to one trigonal bi-pyramidal and two tetragonal interstices that are fully occupied in the saturated deuterides jointly by deuterium and oxygen. After deuterium desorption the oxygen atoms fully return to the initial octahedral site.