Annealing Effect on Synthesis of VO2 (M) Nanopowders by a Novel Solution-Based Process

This paper describes a novel and simple method to preparing monoclinic VO₂ (M) nanopowders via the reaction of ammonium meta-vanadate (NH₄VO₃) and oxalic acid dihydrate (C₂H₂O₄•2H₂O). The products were characterized by means of methods. XRD results show that well crystallized nanopowders of the monoclinic VO₂ (M) were successfully synthesized, while the molar ratio between NH₄VO₃ and C₂H₂O₄•2H₂O was kept at 1:0.5~2.5, and the annealing temperature was 350~750 ℃ for 2~10 hour in nitrogen atmosphere. The spherical morphology of the samples is characterized by SEM. The crystallization temperature of the desired M/R-phase VO₂ is lower than 387 ℃ in this work. And the phase transition temperature is determined by differential scanning calorimetry (DSC).