High-pressure synthesis under giga-pascal hydrogen is attractive method to discover new metal hydrides with high hydrogen storage capacity. Recently, we have succeeded to prepare a series of new hydrides Mg
7MH
x (M=Ti, V, Nb, Hf, Ta,
etc) with a cubic super-lattice structure (Ca
7Ge-type) at 8 GPa and 600°C. One of them, Mg
7TiH
x had the theoretical hydrogen capacity of 6.9 mass%, and exhibited lower hydrogen desorption temperatures of
ca 150°C than MgH
2. The detailed crystal structure analysis showed that the Mg-H interatomic distance in Mg
7TiH
x was longer than that in MgH
2, explaining the lowered desorption temperature.
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