Direct preparation and formation mechanism of belt-like doped VO2(M) with rectangular cross sections by one-step hydrothermal route and their phase transition and optical switching properties

VO2(M) shows a reversible first-order metal-insulator transition to metallic rutile phase VO2(R) at 68 °C. The large-scale and low-cost synthesis of VO2(M) are challenge for materials scientists. In this paper, belt-like W-doped VO2(M) with rectangular cross sections was successfully synthesized using peroxovanadium (V) complexes as the vanadium precursor and ethanol as the reducing agent by a facile one-step hydrothermal approach for the first time. The samples were separately characterized by XRD, EDS, XPS, XRF, SEM, DSC and variable-temperature FTIR. Some parameters, such as the quantity of the dopants, reaction temperature, reaction time, kinds of dopants and volume of ethanol, were briefly discussed to synthesize W-doped VO2(M) solid solution. It is found that doped atoms can be successfully doped into the crystal lattice of VO2 matrix, and the morphologies of the samples are described as highly faceted micro- and nano-belts structures with rectangular cross sections. The formation mechanism of W-doped VO2(M) was discussed in detail. The phase transition temperature of W-doped VO2(M) can be simply tuned by changing the doping concentration of W atom within appropriate limits. The variable-temperature infrared spectra reveal that the doped VO2(M) has outstanding thermochromic characters and optical switching properties.