V2.38Nb10.7O32.7: A V2O5–Nb2O5 mixed oxide tunnel structure related to the tetragonal tungsten bronzes

A crystal structural model for the orthorhombic compound V{sub 2.38}Nb{sub 10.7}O{sub 32.7}, which is known as 'V{sub 2}Nb{sub 9}O{sub 27.5}', was developed by means of selected area electron diffraction (SAED), Rietveld refinement and high resolution electron microscopy (HREM). The metastable compound is obtained by thermal decomposition of freeze-dried precursors as chain-like agglomerated nanoparticles or by reaction of V{sub 2}O{sub 5} with fresh-precipitated Nb{sub 2}O{sub 5} as more compact micro-scaled crystals. With the latter, it was possible to identify its structure for the first time (space group Cmmm). The tetragonal tungsten bronze (TTB)-type structure shows high potential for ionic intercalation, since easily reducible [V{sup 5+}{sub 2}O{sup 2-}] units are implemented in the tunnels of a rigid niobium oxide framework. - Graphical abstract: A crystal structural model for the orthorhombic compound V{sub 2.38}Nb{sub 10.7}O{sub 32.7}, which is known as 'V{sub 2}Nb{sub 9}O{sub 27.5}', was developed by means of selected area electron diffraction, Rietveld refinement and high resolution electron microscopy. In dependence on the synthesis method the metastable compound is obtained as chain-like agglomerated nanoparticles or as more compact micro-scaled crystals. V{sub 2.38}Nb{sub 10.7}O{sub 32.7} is the first and only example of a compound with a TTB-type structure (space group Cmmm) in themore » system V{sub 2}O{sub 5}-Nb{sub 2}O{sub 5}.« less