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).