CEMNALHX, A NEW METAL HYDRIDE

In contrast to CeAl2, which does not form hydrides, and Ce-Mn which do es not form binary intermetallic compounds at all, CeMnAl absorbs cons iderable amounts of hydrogen. A stable hydride phase (beta-phase) is f ormed at low pressures (<10 mbar) with a capacity of about 1.2 H/formu la unit (f.u.). Hydrogen is absorbed up to 2.4 H/f.u. at pressures >10 mbar (at 300 K). In this work we show the absorption characteristics and structural properties of this new metal hydride. The intermetallic compound CeMnAl crystallizes in the cubic C15 Laves phase as observed by X-ray diffraction. Neutron scattering experiments on this intermet allic compound show that the Mn and Al atoms are distributed randomly on the B sites in this AB(2)-type C15 Laves phase compound (A=Ce; B=Mn , Al). Upon hydride (deuteride) formation the C15 structure is preserv ed. The deuterium atoms occupy only the 2A-2B-tetrahedral interstitial sites(96g-positions) over the investigated concentration range 0.0<x less than or equal to 2.5 in CeMnAlDx. (C) 1997 Elsevier Science S.A.