One-step hydrothermal conversion of VO2(B) into W-doped VO2(M) and its phase transition and optical switching properties

W-doped monoclinic vanadium dioxide VO2(M) nanobelts have been transformed from VO2(B) nanobelts in the presence of tungstic acid by a facile one-step hydrothermal route for the first time. The as-prepared samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and variable-temperature infrared spectroscopy (IR). The results show that W atoms are doped into the crystal lattice of VO2(M) matrix, and the morphology and size of the as-obtained VO2(M) nanobelts are dependent on that of the precursor VO2(B). The phase transition temperature (Tc) of W-doped VO2(M) can be tuned by W doping. The variable-temperature IR reveals that the as-synthesized W-doped VO2(M) nanobelts have outstanding thermochromic characters and optical switching properties.