Annealing effect on synthesis of VO ₂ (M) nanopowders by a novel solution-based process

This paper describes a novel and simple method to preparing monoclinic VO ₂ (M) nanopowders via the reaction of ammonium meta-vanadate (NH ₄VO ₃) and oxalic acid dihydrate (C ₂H ₂O ₄·2H ₂O). The products were characterized by means of methods. XRD results show that well crystallized nanopowders of the monoclinic VO ₂ (M) were successfully synthesized, while the molar ratio between NH ₄VO ₃ and C ₂H ₂O ₄·2H ₂O was kept at 1:0.5∼2.5, and the annealing temperature was 350∼750 °C 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 VO ₂ is lower than 387 °C in this work. And the phase transition temperature is determined by differential scanning calorimetry (DSC).