Local structure investigation of cobalt ferrite-based nanoparticles by synchrotron X-ray diffraction and absorption spectroscopy

摘要

In this work, the local structure of ferrite nanoparticles (CoFe2O4) composed of a cobalt ferrite core surrounded by a thin layer of maghemite (CoFe2O4@gamma-Fe2O3) was investigated by crossing analyses of X-ray powder Diffraction (XRD), X-ray Absorption Spectroscopy (XANES/EXAFS) and Diffraction Anomalous Fine Structure (DAFS). The proportion of the core and the shell phases was carefully checked by chemical analysis. The whole of these multiple complementary techniques confirmed the non-equilibrium site occupancy in the cobalt ferrite core. The cation distribution was precisely determined showing that about 15% of cobalt ions are located at tetrahedral sites. The results of EXAFS spectra indicated interatomic distances very close to bulk values. The mean coordination number of both metallic cations was found to be lower than expected for bare nanoparticles and reflected the core-shell structure in CoFe2O4@gamma-Fe2O3 ones. Finally, DAFS analyses were applied to enlighten the local structure around iron atoms in specific Bragg planes.