High-pressure synthesis of novel hydrides in Mg-RE systems and their hydrogen content (RE = Y, La)

New high-pressure hydrides in the MgH2-REH3 systems, where RE = Y and La, have been prepared by using a cubic-anvil-type apparatus, and their detailed crystal structure and hydrogen content have been investigated. The high-pressure synthesis was performed at 800 degreesC under 5 GPa for 2 h. In the Mg-Y system, MgY2H7.8 (H/M approximate to 2.6) with an FCC structure (a = 0,51657(2) nm) have been prepared. Based on the hydrogen content and crystallographic consideration, it was suggested that octahedral sites were partially (approximate to 60%) occupied by H atoms in addition to tetrahedral sites. For this hydride, H atoms on the tetrahedral sites seem to play a role to hold the FCC unit cell. For MgH2 - x mol% LaH3, the new high-pressure hydride was obtained in the range of 25 less than or equal to x less than or equal to 33. Mg3LaH9 was found to have a primitive tetragonal unit cell (a = 0.8172 nm, c = 0.5015 nm).