Abstract: VO₂ nanopowders with various stoichiometries and crystalline states were prepared by pyrolyzing the
precursor, (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O, at low temperature in a mixed flow of air and N₂. The adsorption properties of
crystal, quasi-crystal and amorphous state nano-VO₂-powders were studied. DSC results indicate that VO_2.025 exhibits a phase transition at
70.1℃ and has the maximum phase transition heat in the range from VO_1.985 to VO_2.071. The unit-cell parameters of various stoichiometry VO_x were determined. The results show that the unit-cell volume of the monoclinic VO_x phase increases linearly from
the oxygen-deficient VO₂ to the oxygen-rich VO₂.

Key words: VO₂ nano-powder, stoichiometry, phase transition heat, unit-cell parameter