Ca19Mg8H54, a new salt-like ternary metal hydride

Ca19Mg8H54 and its deuteride have been synthesised at high pressure (25 kbar) and high temperature (850 K) from a 1:2. mixture of the binary Mg and Ca hydrides (deuterides). X-ray and neutron powder diffraction show a cubic Yb19Mg8H54 type structure (space group Im (3) over bar) with cell parameters a=12.1457(6) Angstrom (hydride) and 12.0642(8) Angstrom (deuteride). The hydrogen storage densities (5.4 wt.%, 100.9 g/litre) are among the highest found so far for ternary alkaline earth or mixed alkali-alkaline earth metal hydrides. Desorption experiments suggest that the deuteride decomposes at similar to 700 K and 5 bar deuterium pressure into Ca4Mg3D14 and CaD2. (C) 1999 Elsevier Science S.A. All rights reserved.