Abstract: The violet polycrystalline (NH₄)₅[(VO)₆(CO₂)₄(OH)₉]·10H₂O(Ⅰ) was synthesized by using V₂O₅, HCl, N₂H₄·2HCl and NH₄HCO₃as the starting materials. The yield was 80%-95%. The TG/DTG and DTA of Iwere studied in a flow of N₂. The effects of partial pressure of oxygen(po₂) in N₂-air flow and temperature of reaction on VO₂stoichiometry were investigated in the pyrolysis of Ⅰ in a silica tube. The results show that x value of VO_xis proportional to po₂at pyrolysis temperature of 500 ℃ At po₂= 30.3 Pa and in the temperature range from 450 to 520 ℃ the products are oxygen-deficient VO₂, and when the temperature is lower than 450℃ or higher than 520℃ the products are oxygen-rich VO₂In this paper, various stoichiometry VO₂powders from VO_1.927to VO_2.080were successfully synthesized by pyrolysizing the precursor. XRD patterns of VO₂show that none of the impurity peaks was observed. The SEM micrograph of sample indicates that as-prepared VO₂is spherical particles with mean size 20 nm and is homogeneous in distribution. Further experiments testify that the composition of nano-powders is homogeneous.

Key words: Vanadium dioxide, Nano-powder, Stoichiometry, Preparative route of the precursor