High-pressure synthesis of novel hydrides in Mg–RE–H systems (RE = Y, La, Ce, Pr, Sm, Gd, Tb, Dy)

The high-pressure synthesis of new hydrides of Mg–RE–H systems, where RE = Y, La, Ce, Pr, Sm, Gd, Tb and Dy, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In Mg–Y–H system, newly found MgY2Hy with a FCC-type structure has been prepared. In MgH2–x mol% REH (REH = LaH3, CeH2.5 and PrH3), new hydrides with primitive tetragonal structure were synthesized around x = 25–33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c = 0.4970 nm at x = 25 in Mg–La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1, 3.7 and 3.9 mass% in Mg–La, Ce and Pr systems, respectively, and the chemical formulae were found to correspond to Mg3LaH9, Mg3CeH8.1 and Mg3PrH9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg3LaH9: 614 K, Mg3CeH8.1: 609 K, Mg3PrH9: 630 K) with an endothermic reaction. In MgH2–x mol% hREH (hREH = GdH3, TbH3 and DyH3), new hydrides with FCC-type structure were synthesized around x = 67.