Influence of different additives on the synthesis of VO2 polymorphs

Monoclinic vanadium dioxide VO2(M) shows a fully reversible first-order metal-to-insulator transition (MIT) with the phase transition temperature (Tc) at about 68 °C. The large-scale and low-cost synthesis of VO2(M) are a challenge for materials scientists. In this paper, the influence of different additives on the synthesis of VO2 polymorphs by a hydrothermal route was studied. F, Ti, Cr, Fe, Mo, Sn, Sb and W atoms can promote the formation of VO2(M), while Mg, Al, Co and Ni atoms are favorable for the synthesis of VO2(B), whereas, Na, Ca, Mn and Zn atoms have no influence on the formation of VO2(A). It was found that the Tc of doped VO2(M) is very sensitive to the doped atoms. Some parameters, such as the temperature, reaction time, initial V2O5/oxalic acid molar ratio, tungstic acid concentration, were briefly discussed to give a systematic overview on the synthesis of W-doped VO2(M). In all cases, the morphologies of the doped VO2(M) show micro- and nano-rods structures. The Tc 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 show that the doped VO2(M) has outstanding thermochromic characters and optical switching properties. Furthermore, the enlarged-scale experiments for the synthesis of doped VO2(M) suggest that the same results can be acquired, which makes this route very suitable for practical application.