An extended X-ray absorption fine-structure study was made of nanocrystalline material which had been prepared by high-energy ball-milling. Data analysis was carried out by using a new  ab initio  multiple scattering method. Crystalline Fe, used as a reference, was analyzed by taking account of the important multiple scattering signal. The results of the data analysis were shown to be in good agreement with known structural values. The marked decrease in the first-neighbor coordination number, which was found in nanocrystalline material as a function of the milling time, was shown to be related to the presence of a large defect density. The corresponding decrease in the coordination numbers of the second and more-distant neighbors, as well as a significant decrease in the multiplicities of the 3-atom configurations, confirmed that interpretation. A simple model, which took account of the presence of atomic defects, was shown to lead to a marked reduction in the coordination numbers and 3-atom multiplicities; in agreement with the experimental data. Some models without lattice defects were shown to be unable to provide a quantitative explanation for the intensity reduction, of the extended X-ray absorption fine-structure signal, which was found in milled nanocrystalline Fe. The  in situ  annealing (at up to about 1100C) of samples which had been milled for 32h was shown to reduce considerably the defect density, as expected. However, no complete recovering of the crystalline order was found.

A.Di Cicco, M.Berrettoni, S.Stizza, E.Bonetti, G.Cocco: Physical Review B, 1994, 50[17], 12386-97