Reversible Interconversion of a Divalent Vanadium Bronze between δ and β Quasi-1D Structures

Charge fluctuations along the quasi-1D frameworks of M x V2O5 bronzes have evinced much recent interest owing to the manifestation of colossal metal–insulator transitions and superconductivity. Depending upon the nature of the intercalating cation (M), distinctive geometries of the V2O5 framework are accessible. Herein, we demonstrate an unprecedented reversible transformation between double-layered (δ) and tunnel (β) quasi-1D geometries for nanowires of a divalent vanadium bronze, Ca x V2O5 (x ≈ 0.23), upon annealing-induced dehydration and hydrothermally induced hydration. Such a facile hydration/dehydration-induced interconversion between two prominent quasi-1D structures (accompanied by a change in charge-ordering motifs) has not been observed in the bulk and is posited to result from the ease of propagation of crystallographic slip processes across the confined nanowire widths for the δ → β conversion and the facile diffusion of water molecules within the tunnel geometries for the β → δ reversion.