High-resolution and high-pressure x-ray diffraction study of ScFe2H compounds

Using synchrotron-based x-ray diffraction (SXRD) techniques, the evolution of the crystal lattice in ScFe 2 H x compounds is investigated at room temperature and under pressures up to 25 GPa. High-resolution SXRD experiments reveal that the C14 hexagonal MgZn 2 -type structure of the parent intermetallic compound ScFe 2 is preserved upon H insertion into the crystal structure in spite of the large unit-cell expansion of 21.4 %. The lattice expansion proves to be anisotropic with a larger expansion within the basal plane of the hexagonal structure Δ a / a = 7.1 % against Δ c / c = 5.8 %. This huge increase in the cell volume is equivalent to 2.92 Å 3 /inserted hydrogen atom, a value much larger than that reported for several other Fe-rich alloys. Angle-dispersive SXRD measurements under external pressure indicate that the hexagonal symmetry of the crystalline lattice remains unaltered within the studied compression range up to 25 GPa. No signature of a structural phase transformation has been observed at least up to the highest applied pressure. The application of hydrostatic pressure induces a monotonous contraction of the cell dimensions. A bulk modulus of K 0 = 142 GPa has been inferred from the pressure-volume relationship for the initial alloy ScFe 2 . It is further shown that hydrogen (deuterium) absorption leads to a decrease of the bulk modulus down to K 0 = 112 and 92 GPa for ScFe 2 H 2.8 and ScFe 2 D 3.2 , respectively. • Hexagonal P6 3 /mmc crystal symmetry of ScFe 2 is preserved upon hydrogen insertion. • Large unit cell expansion of Δ V / V = 21.4 % is observed from high resolution synchrotron XRD. • High pressure effect on the hexagonal structure of ScFe 2 H x studied using synchrotron XRD. • No structural phase transition has been observed for ScFe 2 H x up to 25 GPa. • Decrease of the bulk modulus from 142 GPa for ScFe 2 to 92 GPa for ScFe 2 H 3.2 .