Nano Vanadium Dioxide Powder Preparation And Optoelectronic Properties Of Tungsten Doping

As a special function material, vanadium dioxide (VO2) have attracted great interest and been extensively studied. VO2 undergoes a semiconductor-metal phase transition approximately at 68 oC which is near room-temperature. The transition is accompanied with abrupt changes in its electrical and optical properties. The most important is that phase-transition temperature (Tc) of VO2 powders can be gone down to room temperature by doping. So VO2 can be used for a smart window material and energy saved material.To the best of our knowledge, tungsten-doped vanadium dioxide (VO2) nanopowders with reduced transition temperature were synthesized by thermolysis of (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O at low temperature, with active white powdery tungstic acid (WPTA) used as a substitutional dopant for the first time. The products were characterized by XPS, XRD, SEM-EDX, TEM, TG-DTA and DSC. The properties of thermochromic VO2 thin films have been investigated by FT-IR and the four-probe method.DSC and T-R curves of the nanopowders indicated that Tc of VO2 powders was 67.15 oC. However, when WPTA was added into V2O5 (with W/V = 2 atom %), Tc of VO2 decreased markedly from 67.15 oC. to 26.46 oC. which was close to room temperature. The product of W-doped showed the relatively large changes of the optical transmittance and reflectance during the phase transitions that are nearly 56%. The results indicated that WPTA was found to be exceptionally effective as a dopant for reducing transition temperature. Such a low Tc is beneficial to the application and development of smart windows materials.The thermolysis was compared with the other widely accepted preparation techniques. It was found that the thermolysis was a valuable preparation technique for its cheap precursor, simple processes, can be doped tungsten easily, and great potential to produce markedly high quality nanopowders.