DETERMINATION OF LOCAL-STRUCTURE IN NANOPHASE PALLADIUM BY X-RAY-ABSORPTION SPECTROSCOPY

We report a comprehensive investigation of nanophase palladium by x-ra y-absorption spectroscopy with the aim of clarifying the issue of the structure of the grain boundaries in nanophase materials. In fact, sin ce the proposal that the grain boundaries in these materials are highl y 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 o f highly disordered grain boundary regions due to the finding of great ly 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 +/- 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 da ta has been extended up to the eighth coordination shell taking into a ccount the important multiple-scattering paths.