High-Pressure X-ray Studies of the Ni-H, Re-H and Al-H Systems

The room tempearture equations of state of the metallic hydrides NiHx and ReHx have been studied to 123 GPa and of the nonmetallic hydrides AIH3/AID3 to 53 GPa by means of x-ray diffraction in a diamond anvil cell. The partial hydrogen volume in ALH3/AlD3 is found to reduce to that characteristic of metallic hydrides at∼47 GPa. The evolution of the partial hydrogen volume with pressure in the metallic hydrides is discussed in light of existing empirical models.