Large angle x-ray diffraction study of nanocrystalline Pd

This paper reports on quantitative x-ray diffraction measurements of ultrafine-grained (nanocrystalline) Pd and a coarse-grained polycrystalline reference foil that were obtained using synchrotron radiation. The Bragg reflection intensity profiles of nanocrystalline Pd were found to be considerably better represented by Lorentzian functions than by Gaussian functions, indicating that a large fraction of the intensity from the Bragg peaks is located in the tails of the reflections. The intensity that is in the Lorentzian-shaped Bragg peaks differs only slightly for different grain-sized materials; thus, the atomic relaxations in the vicinity of grain boundaries do not produce broadly distributed diffuse scattering other than that found in the Bragg reflections. The results of the present work do not support the previously proposed existence of either a gas-like grain boundary phase, or large quantities of vacancies or voids within grains of nanocrystalline Pd