High-Pressure Synthesis, Crystal Structures, and Hydrogenation Properties of MgYNi and (Mg,Y)2Ni Compounds

This study presents two new structures of compounds in the Mg–Y–Ni ternary system, MgYNi with a hexagonal ZrNiAl-type structure and Mg_2–xY_xNi with an orthorhombic Mg₂Cu-type structure, both obtained through a high-pressure synthesis technique at GPa-order pressures. MgYNi with the ZrNiAl-type structure underwent a phase transformation into an orthorhombic MoAlB-type structure at 622 K in an Ar atmosphere via an exothermic reaction. Additionally, MgYNi with the ZrNiAl-type structure exhibited hydrogen absorption at 313 K under 5 MPa H₂ and formed MgYNiH_∼4.7 with the ZrNiAl-type structure, resulting in volume expansion of approximately 24.7%. Mg_2–xY_xNi with the Mg₂Cu-type structure was obtained at 0.12 < x < 0.26. Hydrogenation of Mg_2–xY_xNi with the Mg₂Cu-type structure at 598 K and 8 MPa resulted in decomposition into monoclinic and orthorhombic phases of Mg₂NiH₄ along with YH₃ and Ni. Hydrogen desorption temperature of the hydrogenated Mg_2–xY_xNi was approximately 50 K lower than that of Mg₂Ni after hydrogenation.