Formation of vanadium oxides with various morphologies by chemical vapor deposition

We reported the formation of vanadium oxides with various morphologies, including V2O5 rods, VOx microspheres, VO2 microblocks etc., by chemical vapor deposition using vanadyl acetylacetonate (VO(acac)(2)) powder as a vanadium precursor. The obtained samples were characterized by scanning electron microscopy (SEM), Raman scattering and X-ray diffraction (XRD). Results revealed that the morphologies and microstructures of vanadium oxides were significantly dependent on the depositing temperature. V2O5 rods with a diameter of similar to 250 nm, VOx microstructure with V5+ and V4+ cations and VO2 microblocks were obtained at the depositing temperature of 500, 450-250 and 150 degrees C, respectively. VO2 structures were formed at the beginning of growth process, and V4+ cations were partially oxidized to V5+ cations at the higher depositing temperature (250-450 degrees C). Various morphologies of VOx were attributed to the mixed microstructure of V2O5 and VO2. The difference between V4+-O and V5+-O bonds induced the distortion and various structures in VOx. When the depositing temperature was as high as 500 degrees C, most of the V4+ cations were oxidized to V5+ cations and V2O5 rods were obtained. (C) 2008 Elsevier B.V. All rights reserved.