Neutron diffraction study of the Pd0.772Ag0.228Dν membrane for hydrogen separation

Abstract Experiments of deuterium absorption/desorption were performed on a foil of Pd 77 Ag 23 (wt%) alloy in the 78–196 °C temperature and 1–4 bar pressure ranges under the neutron beam at ILL (Grenoble). Powder diffraction patterns were collected on the D1B diffractometer ( λ  = 1.2871 A) on the Pd 0.772 Ag 0.228 D ν deuterated alloy, and the face-centred-cubic structure was Rietveld-refined locating the D atom in the octahedral site with a variable occupancy ν (=D/M ratio). The results of ν ( T ) curves at different p (D 2 ) pressures are discussed in comparison with literature data on H and D absorption into Pd Ag alloys from thermodynamic measurements. A negative deviation from predictions of Sieverts' law is shown by the dependence of D occupancy on pressure. This effect relates the behaviour of the activity coefficient γ D to D–D and D–M interactions in the solid solution phase.