Synthesis, structure and properties of printable W-doped thermochromic VO2 with a low phase transition temperature

Vanadium dioxide (VO2) could be a good candidate for thermochromic materials due to the characteristic features of phase transition and discoloration. However, the high phase transition temperature (Tc) of 68 degrees C becomes the limitation of its practical application. In this work, a cost-effective fabrication method was developed to prepare W-doped thermochromic VO2 with a low phase transition temperature. Herein, tungsten (W) was introduced into an O-V-O system via a simple hydrothermal method, followed by annealing in an argon atmosphere to reduce the Tc of VO2. The results show that the micromorphology of VO2 changed significantly from rectangular to continuous sheet-like and that the particle size was increased after W-doping. Annealing could decrease the size of undoped VO2, and the morphology became an inhomogeneous and disordered cusplike shape. In addition, annealing made the W-doped VO2 particles with a larger size exhibit crimps, shrinkage and collapse. The Tc of VO2 (M phase to R phase) was reduced to 34.3 degrees C, 18.6 degrees C and 10.6 degrees C with W-doping levels of 1.5 at%, 2.0 at% and 3.0 at% at annealing temperatures of 500 degrees C, 550 degrees C and 500 degrees C, respectively. Infrared spectra indicate that the largest integrated infrared transmittance was increased from 51.78% to 81.91% (sample of S-22). Therefore, W-doped thermochromic VO2 could be a promising candidate for applications in printing, sensors and optical devices as functional materials.