Zr4Al3D2.68 and Zr3Al2D2.26: new Zr-containing intermetallic hydrides with ordered hydrogen sublattice

Abstract Two hydrogenated intermetallics with the highest Al/Zr ratio among the hydrogen-absorbing Zr–Al compounds, Zr 4 Al 3 and Zr 3 Al 2 , have been studied by synchrotron X-ray, powder neutron diffraction and thermal desorption spectroscopy. Initial intermetallic compounds are quite different with respect to Al–Al interactions and contain plain Kagome Al nets (Zr 4 Al 3 ) or Al–Al pairs (Zr 3 Al 2 ). In hexagonal Zr 4 Al 3 D 2.68 (space group (s.g.) P 6 3 22; a =11.0017(4); c =11.1694(5) A) a 2 a ×2 a ×2 c superstructure is formed as a result of deuterium ordering in half of the available Zr 4 tetrahedra. These tetrahedra share common corners and edges and form layers separated by 6363 Al-nets. In tetragonal Zr 3 Al 2 D 2.26 (s.g. P 4 2 / mnm ; a =7.5970(3); c =7.2613(3) A) in addition to the completely filled Zr 4 tetrahedra hydrogen partially occupies Zr 3 triangular sites. Thermal stability of the studied deuterides and Zr–D bonding characteristics can be related to the size of the occupied Zr 4 tetrahedra. Higher thermal stability of Zr 3 Al 2 D 2.26 agrees well with the existence of large Zr 4 sites and contrasts to the behavior of Zr 4 Al 3 D 2.68 containing ‘contracted’ Zr 4 tetrahedra and having weaker Zr–D bonds.