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

Magnesium-based hydrides with Zr or Hf have been synthesized by means of an ultra-high pressure technique. Powder mixtures of MgH2 and ZrH2 or HfH2 have been heated up to 873 K under 4–8 GPa in a multi-anvil cell. New ternary phases (Mg–Zr–H and Mg–Hf–H) with a face centered cubic (FCC) structure have been formed. In the Mg–Zr hydride, the FCC phase with disordered metal–atom occupancy was observed, while a Ca7Ge-type super-lattice structure was observed in the Mg–Hf hydride. By the temperature programmed desorption (TPD) measurements, these new hydrides exhibit the hydrogen-desorption at around 543–583 K, which were 130–70 K lower than that of MgH2 at a heating rate of 10 K/min under vacuum. Desorbed hydrogen contents were estimated to be 4.2 and 3.0 mass% for Mg–Zr and Mg–Hf hydrides, respectively.