The hydrogenation of Dy5Pd2 followed by in situ methods

The hydrogenation behavior of the intermetallic compound Dy5Pd2 was investigated by means of ex situ X-ray powder diffraction, in situ neutron powder diffraction and in situ differential scanning calorimetry. The structural model of Dy5Pd2 with a palladium atom at the 32(e) position x, x, x (x≈0.22, 7/8 occupation) and a dysprosium atom at almost the same location (x≈0.18, 1/8 occupation) is confirmed. Upon heating the latter approaches x(Pd) and at T=399 K both positional parameters are indistinguishable. Dy5Pd2 does not incorporate hydrogen (deuterium) into its crystal structure, however, starting at T=495 K reacts with hydrogen to non stoichiometric dysprosium dideuteride, DyD2+x, following a parabolic rate law. In situ differential scanning calorimetry at various hydrogen pressures up to 2.5 MPa shows strongly exothermic signals, whose temperature onset depend on the gas pressure, corresponding to the formation of a mainly ionic hydride (DyH2+x).