Site occupancy of Fe2+, Fe3+ and Ti4+ in "titanomagnetite" determined by valence‐difference contrast synchrotron X‐ray

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Marco E. Ciriotti
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Site occupancy of Fe2+, Fe3+ and Ti4+ in "titanomagnetite" determined by valence‐difference contrast synchrotron X‐ray

Messaggio da Marco E. Ciriotti » sab 10 nov, 2018 14:10

▪ Okube, M., Oshiumi, T., Nagase, T., Miyawaki, R., Yoshiasa, A., Sasaki, S., Sugiyama, K. (2018): Site occupancy of Fe2+, Fe3+ and Ti4+ in titanomagnetite determined by valence‐difference contrast in synchrotron X‐ray resonant scattering. Journal of Synchrotron Radiation, 25, 1694-1702.

A synchrotron X‐ray diffraction study of a single crystal of titanomagnetite shows that the cation distribution of Fe2+, Fe3+ and Ti4+ is of the inverse‐spinel type. The valence‐difference contrast (VDC) method of resonant scattering was applied at a wavelength of λ = 1.7441 Å (E = 7.1085 keV) within the pre‐edge of the Fe K absorption spectrum, utilizing the large difference in the real part of anomalous scattering factors, between −7.45 and −6.50, for Fe2+ and Fe3+, respectively. The most plausible atomic arrangement in Ti0.31Fe2.69O4 obtained from our analysis is [Fe3+1.00]A[Fe3+0.38Fe2+1.31Ti4+0.31]BO4, where A and B in an AB2O4‐type structure correspond to the tetrahedral and octahedral sites, respectively. This result suggests that titanomagnetite has the complete inverse‐spinel structure continuously from the end‐member of magnetite, even in the case of relatively high Ti content. The physical properties may be described by the Néel model, which claims that Fe3+ preferentially occupies the tetrahedral site, within a Ti‐poor half‐region of the solid solution. Based on the ordering scheme the magnetic structure of titanomagnetite is considered to be analogous to that of magnetite. The combination of circularly polarized X‐rays and a horizontal‐type four‐circle diffractometer used in this VDC technique has the advantage of increasing the experimental accuracy and freedom with the simultaneous reduction of experimental noise.
Marco E. Ciriotti

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