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

•Deuterium occupies octahedral sites in the FCC structure of the Pd77Ag23 alloy.•D occupancy decreases with temperature and increases with pressure.•D uptake at 1 bar is enhanced by previous sample treatment at higher pressure.•Observed deviations from Sieverts' law are ascribed to D-D repulsion in the structure.

Experiments of deuterium absorption/desorption were performed on a foil of Pd77Ag23 (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 Å) on the Pd0.772Ag0.228Dν 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(D2) pressures are discussed in comparison with literature data on H and D absorption into PdAg 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 γD to D-D and D-M interactions in the solid solution phase.