High Pressure Synthesis of Novel Mg(Ni<SUB>1&minus;<I>x</I></SUB>Cu<I><SUB>x</SUB></I>)<SUB>2</SUB> Hydrides (<I>x</I>=0&ndash;0.2)

Abstract

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 MgNi 2 was studied on the crystal structures, thermal stabilities and hydrogen contents of Mg(Ni 1Àx Cu x ) 2 hydrides (x ¼ 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 ¼ 0:0{0:1) and body-centered tetragonal structures (I4=mmm, x ¼ 0:15{0:2). Their hydrogen contents were estimated to be 2.23-2.32 mass%. Dehydrogenation temperature decreased from 460 K (x ¼ 0:0) to 429 K (x ¼ 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 1Àx Cu x ) 2 could be hydrogenated reversibly without disproportionation under high pressure of the order of gigapascals.