The microstructure of hydrogen- and deuterium-doped nanocrystalline palladium studied by small-angle neutron scattering

By means of small-angle neutron scattering the microstructure of two nanocr ystalline Pd samples (prepared by inert gas condensation) has been studied at room temperature in a Q-range from 10(-3) Angstrom(-1) to 0.4 Angstrom(- 1) An additional subsequent doping of the two samples with H as well as wit h D (concentrations < 4 at%) caused contrast variations that provided more detailed structural information. The measured scattering intensity was mode led by a Pored contribution from large heterogenities (e.g. pores) and a co ntribution from spherical grains with a log-normal distribution of their ra dii. To account for the presence of grain boundaries, the grains were consi dered to be surrounded by a shell with a reduced Pd density and a thickness half as large as the thickness of the grain boundaries. For the above mode l, the data of the H-doped, D-doped and undoped sample were simultaneously fitted with one single set of adjustable parameters. The fits yielded for t he two samples volume-weighted mean grain radii of 10 nm and 13 nm. The val ues for the grain boundary thickness lie between 0.2 and 0.8 nm. Almost all of the H- and D-atoms are, at low hydrogen concentrations, located in the grain boundaries.