Structural Phase Transition of Tungsten-Doped Vanadium Dioxide Nanopowders Prepared by Thermolysis

摘要

Tungsten-doped vanadium dioxide (VO{sub}2) nanopowders were prepared by thermolysis of (NH{sub}4){sub}5[(VO){sub}6(CO{sub}3)4(OH){sub}9]·10H{sub}2O at low temperature, with active white powdery tungstic acid used as a substitutional dopant. The composition and microstructure of the powders were examined by X-ray diffraction, transmission electron microscope, and differential scanning calorimetry. The change in electrical resistance due to the S-M transition was measured from 0 to 150℃ by the four-probe method. Hysteresis loops and differential scanning calorimetry analysis of the samples indicated that the phase-transition temperature of VO{sub}2 nanopowders was 67.15℃. For tungsten-doped VO{sub}2 nanopowders, the temperature was reduced to 26.46℃. After sintering the nanopowders, Tc rose from 26.46℃ to 34.85℃ with the sizes increasing to the bulk. A significant direct correlation between particle size and Tc was confirmed. The results indicated that white powdery tungstic acid is exceptionally effective as a dopant for reducing transition temperature.