Determination of Local Structure in Monofase Palladium by X-Ray Absorption Spectroscopy

We report a comprehensive investigation of nanophase palladium by x-ray-absorption spectroscopy with the aim of clarifying the issue of the structure of the grain boundaries in nanophase materials. In fact, since the proposal that the gain boundaries in these materials are disordered, various techniques have obtained conflicting results on this issue. Until two recent brief reports (one of which was our own) x-ray-absorption spectroscopy investigations have supported the view of highly disordered grain boundary regions due to the finding of greatly reduced average coordination number. Contrary to previous reports we find that the reduction in average coordination numbers is smaller that previously reported (at most 4�0.03% for the first shell) and can be explained by a size effect due to the non-negligible interface-to-bulk ratio of the samples. The analysis of the x-ray-absorption data has been extended up to the eight coordination shell taking into account the important multiple-scattering path.