Residual-density mapping and site-selective determination of anomalous scattering factors to examine the origin of the Fe K pre-edge peak of magnetite

The electron‐density distribution and the contribution to anomalous scattering factors for Fe ions in magnetite have been analyzed by X‐ray resonant scattering at the pre‐edge of Fe K absorption. Synchrotron X‐ray experiments were carried out using a conventional four‐circle diffractometer in the right‐handed circular polarization. Difference‐Fourier synthesis was applied with a difference in structure factors measured on and off the pre‐edge (Eon = 7.1082 keV, Eoff = 7.1051 keV). Electron‐density peaks due to X‐ray resonant scattering were clearly observed for both A and B sites. The real part of the anomalous scattering factor f′ has been determined site‐independently, based on the crystal‐structure refinements, to minimize the squared residuals at the Fe K pre‐edge. The f′ values obtained at Eon and Eoff are −7.063 and −6.682 for the A site and −6.971 and −6.709 for the B site, which are significantly smaller than the values of −6.206 and −5.844, respectively, estimated from the Kramers–Kronig transform. The f′ values at Eon are reasonably smaller than those at Eoff. Our results using a symmetry‐based consideration suggest that the origin of the pre‐edge peak is Fe ions occupying both A and B sites, where p–d mixing is needed with hybridized electrons of Fe in both sites overlapping the neighbouring O atoms.