Pure Single-Crystal Rutile Vanadium Dioxide Powders: Synthesis, Mechanism and Phase-Transformation Property

Pure single-crystal rutile-type VO(2) has been synthesized via the hydrothermal reaction Of V(2)O(5), oxalic acid, and tungstenic acid at low temperatures. The products have been characterized by means of X-ray diffraction, transmission electron microscopy, scanning electron microscopy, selected area electron diffraction, differential scanning calorimetry, and X-ray photoelectron spectroscopy. It is shown that a part of VO(2) powders have a "snowflake" morphology assembled by VO(2) rods which have a monoclinic structure with a preferential orientation along (110) direction. The adulterating agent tungstenic acid plays a key role in the synthesis of rutile phase. The DSC results indicated that the metal-semiconductor transition temperature Of VO(2) powders was reduced to room temperature or below. The reaction details and mechanisms are described and discussed. The substitution of a part of V atoms with larger W atoms induces the distortion of the VO(6) octahedra, promoting the transition from VO(2) (B) to VO(2) (R).