Crystal structures and hydrogen-induced decomposition of La(Mg1−xAlx)3 alloys

The crystal structures and hydrogenation behavior of La(Mg1−xAlx)3 (x = 0.1, 0.2, 0.3 and 0.4) alloys have been studied. A new ternary compound La6Mg22Al was found in these alloys. La6Mg22Al crystallizes with the Th6Mn23-type structure in space group Fm3¯m (No. 225). The lattice parameter was calculated to be a = 14.6056(6) Å. The solubility of Al in the La6Mg22Al phase is small, but this Th6Mn23-type structure does not exist in the binary La–Mg system. The La(Mg1−xAlx)3 alloys contain LaMg3, La(Mg,Al)2 and La6Mg22Al when x is from 0.1 to 0.3. As x increases to 0.4, the alloy consists of La(Mg0.29Al0.71)2 and La6(Mg0.955Al0.045)22Al. All the phases decompose into LaH3, MgH2 and La3Al11 under hydrogen atmosphere at 473 K.