Direct synthesis of a ternary superhydride, YxFeyHz compound: structure and metastability

The aim of this proposal is to obtain a ternary hydride by mixing two metals that are known to form binary superhydrides. In hydrogen at Mbar pressures, Y and Fe form binary superhydrides, respectively: YH6 with a cage-like H sublattice [5], and FeH5 with atomic H layers [6]. We will thus search for a ternary superhydride in the Y-Fe-H system. This is a continuation of the proposal HC-5070 in which a remarkable uptake of hydrogen under pressure by YFe2 up to YFe2H7 has been characterized. Hints for a transition to a YxFeyHz compound have been observed above 60 GPa. The beamtime will be devoted to solving the structure of YxFeyHz by single-crystal XRD and to measuring its equation of state and metastability range by decreasing pressure to ambient condition. Other compounds will be searched by exploring the 60-160 GPa range. Ab-initio calculations will then be performed to determine the structure of the H sublattice.