Fe2+ and Fe3+ ions distinguishable by x-ray anomalous scattering: Method and its application to magnetite

Abstract

A chemical shift of about 5 eV was observed between ferrous and ferric ions in the XANES absorption spectra of FeO and Fe₂O₃ where the Fe ions coordinate in regular octahedra. Experimental f^’_e was estimated based on the cross‐section data in the 108 eV region at the Fe K edge using the Cromer and Liberman’s equation. The result shows that the maximum difference in f^’_e between Fe²⁺ and Fe³⁺ is about 2.5 at the longer wavelength side of the Fe²⁺K edge. The XANES spectrum of Fe₃O₄ (magnetite) lies between those of FeO and Fe₂O₃. Synchrotron x‐ray‐diffraction data of a magnetite crystal were measured on a vertical‐type four‐circle diffractometer and used for evaluation at seven wavelengths of 1.7415, 1.7420, 1.7425, 1.7431, 1.7452, 1.7499, and 1.7567 Å. The difference‐Fourier technique promises the possibility of mapping valence differences for atoms of the same atomic species in a mixed‐valence crystal.