FE2+ AND FE3+ IONS DISTINGUISHABLE BY X-RAY ANOMALOUS SCATTERING - METHOD AND ITS APPLICATION TO MAGNETITE

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 Fe 2+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. © 1995 American Institute of Physics.