Nanocomposite structure of two-line ferrihydrite powder from total scattering

• Published in: Communications chemistry Vol. 3; no. 1; p. 22
• Main Authors: Funnell, Nicholas P., Fulford, Maxwell F., Inoué, Sayako, Kletetschka, Karel, Michel, F. Marc, Goodwin, Andrew L.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 21.02.2020; Nature Publishing Group; Springer Nature
• Subjects: 639/301/1034/1035; 639/638/169/209; 639/925/357/354; 639/925/930/12; Atomic structure; Atomistic models; Characterization and analytical techniques; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Computer simulation; Crystal structure; Crystallinity; Geochemistry; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Iron; Multiphase; Nanocomposites; Nanoparticles; Scattering
• ISSN: 2399-3669; 2399-3669
• DOI: 10.1038/s42004-020-0269-2

Ferrihydrite is one of the most important iron-containing minerals on Earth. Yet determination of its atomic-scale structure has been frustrated by its intrinsically poor crystallinity. The key difficulty is that physically-different models can appear consistent with the same experimental data. Using X-ray total scattering and a nancomposite reverse Monte Carlo approach, we evaluate the two principal contending models—one a multi-phase system without tetrahedral iron(III), and the other a single phase with tetrahedral iron(III). Our methodology is unique in considering explicitly the complex nanocomposite structure the material adopts: namely, crystalline domains embedded in a poorly-ordered matrix. The multi-phase model requires unphysical structural rearrangements to fit the data, whereas the single-phase model accounts for the data straightforwardly. Hence the latter provides the more accurate description of the short- and intermediate-range order of ferrihydrite. We discuss how this approach might allow experiment-driven (in)validation of complex models for important nanostructured phases beyond ferrihydrite. Although a geologically important mineral, the atomic-scale structure of ferrihydrite remains unresolved. Here the authors combine X-ray total scattering and reverse Monto Carlo to evaluate the two principal contending models, explicitly considering the material’s complex nanocomposite structure.