VO₂ (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

Well crystallized VO₂ (A) microrods were grown via a single step hydrothermal reaction in the presence of V₂O₅ and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO₂ (A) micro rods. The structural and electronic transitions in VO₂ (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO₂ (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO₂ (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO₂ (M1) are described.