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 grain boundaries in these materials are highly 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 numbers. Contrary to previous reports we find that the reduction in average coordination numbers is smaller than previously reported (at most $4\pm 0.03\%$ 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 eighth coordination shell taking into account the important multiple-scattering paths.

• Received 20 June 1997

DOI:https://doi.org/10.1103/PhysRevB.57.3365