Synthesis of FCC Mg–Ta hydrides using GPa hydrogen pressure method and their hydrogen-desorption properties

Magnesium–tantalum ternary hydrides with an FCC structure were prepared by an ultra high-pressure technique. The FCC Mg–Ta hydride phases with the Ca7Ge-type super-lattice structure were formed at 4 and 8 GPa. Another new phase, Mg3TaHy, was also verified by XRD and SEM in the specimen prepared at 8 GPa. From the temperature-programmed desorption (TPD) measurements with a heating rate of 10 K/min under vacuum, the FCC hydride exhibited hydrogen desorption of ca. 3.1 mass% at an onset temperature of 583 K. When the FCC hydride phase coexisted with Mg3TaHy, simultaneous decomposition occurred and the hydrogen-desorption temperature was lowered to 543 K. The hydrogen-desorption temperatures of the Mg–Ta FCC hydrides were 130–170 K lower than that of MgH2.