The Crystal Structure of Pure and Deuterated Zr₅Al₃O_0.5Dx (X = 0, X = 2.7)

The crystal structures of Zr5Al3Oo.5 and Zr₅Al₃o_0.5D_2.7 have been determined and refined by the Rietveld method from neutron powder diffraction data. Zr₅Al₃o_o.5 crystallizes in the hexagonal “filled” Ca₅Pb₃ type structure, space group F₆₃mc, with the unit cell dimensions a = 14.1552(5) A and c = 5.6862(4) Å, = 6. The dissolved deuterium atoms in Zr₅Al₃O_0.5D_2.7 occupy different types of interstices between the metal atoms and the unit cell dimensions increase to a = 14.2470(13) Å and c = 5.7814(6) Å. The deuterium atoms were found to be distributed on eight crystallographically nonequivalent positions, out of which two are octahedrally surrounded by six zirconium atoms, two are coordinated by three zirconium atoms and two aluminium atoms and the remaining deuterium atoms have three zirconium and one aluminium near neighbours in a tetrahedral arrangement.