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Anti-NASICON Fe2(MoO4)3 (P21/c) shows significant structural and electrochemical differences in the intercalation of Li+ and Na+ ions. To understand the origin of this behavior, we have used a combination of in-situ X-ray and high-resolution neutron diffraction, total scattering, electrochemical measurements, density functional theory calculations, and symmetry-mode analysis. We find that for Li+-intercalation, which proceeds via a two-phase monoclinic-to-orthorhombic (Pbcn) phase transition, the host lattice undergoes a concerted rotation of rigid polyhedral subunits driven by strong interactions with the Li+ ions, leading to an ordered lithium arrangement. Na+- intercalation, which proceeds via a two-stage solid solution insertion into the monoclinic structure, similarly produces rotations of the lattice polyhedral subunits. However, using a combination of total neutron scattering data and density-functional theory calculations, we find that while these rotational distortions upon Na+ intercalation are fundamentally the same as for Li+ intercalation, they result in a far less coherent final structure, with this difference attributed to the substantial difference between the ionic radii of the two alkali metals.
Zhou, S., Barim, G., Morgan, B. J., Melot, B. C., & Brutchey, R. L. (2016). Influence of rotational distortions on Li+- and Na+- intercalation in anti-NASICON Fe2(MoO4)3. Chemistry of Materials, 28(2), 4492-4500. https://doi.org/10.1021/acs.chemmater.6b01806