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

Abstract

This study presents two new structures of compounds in the Mg−Y−Ni ternary system, MgYNi with a hexagonal ZrNiAl-type structure and Mg2-xYxNi 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, 2 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%. Mg2-xYxNi with the Mg2Cu-type structure was obtained at 0.12 < x < 0.26. Hydrogenation of Mg2-xYxNi 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 Mg2-xYxNi was approximately 50 K lower than that of Mg2Ni after hydrogenation.journal articl