High pressure synthesis of novel Mg(Ni_1-xCu_x) ₂ hydrides (x = 0-0.2)

In our previous papers, we have reported the hydrogenation of MgNi ₂ with C36-type structure under GPa-order hydrogen pressure. In this paper, the effect of Cu substitution in MgNi₂ was studied on the crystal structures, thermal stabilities and hydrogen contents of Mg(Ni _1-xCu_x)₂ hydrides (x = 0-0.2). The hydrides were obtained by high pressure synthesis using cubic-anvil-type apparatus at 973 K for 8 h under 5 GPa. The hydrides were found to have primitive orthorhombic (Pmmm, X = 0.0-0.1) and body-centered tetragonal structures (JA/mmm, X = 0.15-0.2). Their hydrogen contents were estimated to be 2.23-2.32 mass%. Dehydrogenation temperature decreased from 460 K (x = 0.0) to 429 K (x = 0.20) with increasing amount of Cu substitution. After dehydrogenation, the C36-type phase was observed by X-ray diffraction (XRD). Consequently, it is noteworthy that Mg (Ni_1-xCu_x) ₂ could be hydrogenated reversibly without disproportionation under high pressure of the order of gigapascals.