Abstract
The set of compositions with Fe2+ in the system NaxFex/2Ti2–x/2O4 has been prepared by solid-state reactions in the inert atmosphere at 1050 °С. The oxidation state of iron was confirmed using the XANES method. Na0.88Fe0.44Ti1.56O4 is the new four-element compound in Na2O–“FeO”–TiO2 system. According to the X-ray powder data, it is orthorhombic, Pnma, a = 9.3624(1), b = 2.96718(4), c = 11.3435(1) Å and has the same structure as Na0.9Fe0.9Ti1.1O4 with Fe3+. The structure was refined by the Rietveld method. The 3D-framework of (Fe, Ti)O6 octahedra contains quadruple rutile-like chains and sodium ions in double tunnels. Fe/Ti partial ordering in the framework and sodium distribution in the tunnels were studied additionally using the method of bond valence sums and Voronoi tessellation. The structure and composition of Na0.88Fe0.44Ti1.56O4 make it a promising material for cathode application.
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