High Pressure Synthesis of Novel Mg(Ni_1−xCu_x)₂ Hydrides (x=0–0.2)

抄録

In our previous papers, we have reported the hydrogenation of MgNi₂ 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 (I4⁄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.