Structural Refinement and Density Functional Theory Study of Synthetic Ge-Akaganeite (beta-FeOOH)

In this study, we propose a revised structural model for highly ordered synthetic Ge-akaganeite, a stable analogue of tunnel-type Fe-oxyhydroxide, based on the Rietveld refinement of synchrotron X-ray diffraction data and density functional theory with dispersion correction (DFT-D) calculations. In the proposed crystal structure of Ge-akaganeite, Ge is found not only in the tunnel sites as GeO(OH)(3)(-) tetrahedra, but also 4/5 of total Ge atoms are in the octahedral sites substituting 1/10 of Fe. In addition, the tunnel structures are stabilized by the presence of hydrogen bonds between the framework OH and Cl- species, forming a twisted cube structure and the GeO(OH)(3)(-) tetrahedra corner oxygen, forming a conjugation bond. The chemical formula of the synthetic Ge-akaganeite was determined to be (Fe7.2Ge0.8)O-8.8(OH)(7.2)Cl-0.8(Ge(OH)(4))(0.2).