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Keywords:

  • X-ray resonant scattering;
  • Fe3O4;
  • magnetite;
  • Fe K absorption edge;
  • anomalous scattering factor;
  • electron-density distribution

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 pd mixing is needed with hybridized electrons of Fe in both sites overlapping the neighbouring O atoms.