In Situ Characterization on Thermal Transitions of VO2(B): Toward VO2(R) and V2O3

VO2(B) was synthesized via a facile hydrothermal process using V2O5 and oxalic acid. The crystal structure and the phase transition of VO2(B) during elevated temperatures in N2 were investigated by in situ X-ray diffraction (XRD). Meanwhile, the morphologies and the crystal structures of the samples obtained by annealing at different temperatures were characterized by Field emission scanning electron microscopy (FE-SEM), XRD and Raman spectroscopy, respectively. The results show that the as-synthesized nano platelet-like monoclinic VO2(B) irreversibly transforms into submicron and micron subsphaeroidal tetragonal VO2(R) between 430 and 700 °C. The as-obtained VO2(R) starts to decompose and form Magnéli phases VnO2n−1 (3≤n≤9) series compounds at ≈1000 °C, and totally transfers into a corundum V2O3 sintered block at ca. 1200 °C.