EXAFS studies of nanostructured Finemet-type alloys

The nanostructure of nanocrystalline Fe66Cr8Cu1Nb3Si13B9 alloys has been studied using extended X-ray absorption fine structure (EXAFS) and analyzed by the cumulant method. Application of the cumulant method enables us to determine the nearest-neighbor interatomic distance and the coordination number for chromium and copper atoms, and thus we are able to obtain detailed knowledge about the role of both Cr and Cu in the structure of nanocrystals at various stages of crystallization. A detailed analysis of the distribution of alloying elements in the grains and grain boundaries reveals the accumulation of Cr in the surrounding of Fe(Si) nanocrystals. The presence of Cr in the surroundings of Fe(Si) can influence the content's arrangement of the nanograins, allowing diffusion of Si atoms in the grain boundaries. Simulated X-ray absorption spectra of the model produced by FEFF9.05 and the proposed Cu clustering of 19 atoms with average cluster size of about 0.4 nm show a good resemblance to the experimental data of the Cu k-edge.