Snowflake-Like Monoclinic VO2 Powders: Hydrothermal Synthesis, Characterization and In Situ Monitoring Phase-Transition Behavior

Vanadium dioxide can transit from semiconductor to metal state at about 68 degrees C accompanying with great change of optical and electrical properties. In this work, snowflake-like VO2 (M) powders were prepared via onestep hydrothermal approach. The crystalline structure, surface morphology, valence state of the derived VO2 powders were characterized via X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that monoclinic phase VO2 was successfully prepared under the optimized conditions. The formation mechanism of the snowflake-like VO2 (M) powders was also discussed. Furthermore, the reversible phase-transition properties of VO2 (M) powders were studied by differential scanning calorimetry and in-situ X-ray diffraction. It is found that the temperature-driven structural phase transitions between monoclinic phase and tetragonal phase can be clearly observed in situ XRD. And the phase-transition performances of VO2 (M) powders have not decreased after 10 heating-cooling cycles in air atmosphere. All of these results imply that VO2 (M) materials can be a potential material access to thermochromic applications such as adaptive camouflage coatings.