Crystal Structure, Cation Distribution and Oxidation State of Spinel Ferrite Nanoparticles: A Synchrotron XRD and XANES Study

The spinel ferrite nanoparticles including Ni_1−x Cu _x Fe²O⁴ (with x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1), NiLa_0.1Fe_1.9O₄ and NiY_0.1Fe_1.9O₄ were prepared by different chemical methods with different fabrication conditions. The crystal structure, cation distribution and oxidation state of the samples were characterized by a combination of Synchrotron X-ray diffraction (SXRD) and X-ray absorption near edge spectrum (XANES). All the crystal structure information such as lattice parameters, coordinates of atoms, ion occupancy and parameters of microstructure have been determined from SXRD data on applying the full pattern fitting of Rietveld method using FullProf program. The refinement result indicates that all the samples have mixed spinel structure in which the rare earth ions locate only in the octahedral sites, while copper and nickel ions occupy both tetrahedral and octahedral sites. The oxidation state of iron and copper in the samples was identified from the XANES analysis at the Fe and Cu K-edges. The obtained results have been discussed and compared with the available data.