In the field of thermochromic materials, monoclinic vanadium dioxide (VO₂) has attracted great attention due to its unique characteristics, exhibiting a Metal to Insulator Transition (MIT) at a critical temperature of Tc = 68^oC, the closest to room temperature among the other phase change metal oxides. MIT is primarily a reversible crystal structure transition from the monoclinic phase, VO₂ (M), at temperature below Tc, to the tetragonal rutile, VO₂ (R), at values above Tc. Along with the structural changes, electronic and optical properties change too, with VO₂ (M) being insulating and IR-transparent while VO2 (R) is metallic and IR-reflective. These intrinsic properties make this material ideal for phase-changing applications where reversibility and the external temperature as stimuli are essential, such as thermochromic coatings for ‘smart’ windows.

In this work, evaluation of different methods towards thermochromic coatings were carried out. In the first part, the effect of the reducing agent used on the hydrothermal synthesis of thermochromic vanadium dioxide powders was investigated. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Differential Scanning Calorimetry (DSC) characterization techniques were employed to determine the structure, morphology and thermochromic performance of vanadium dioxide. Among different reducing agents, oxalic acid led to monoclinic vanadium dioxide with better thermochromic characteristics. After the optimization of the synthetic process, the product with optimum results was selected for the preparation of films to study their thermochromic properties. The implementation of a post-processing step of ball-milling was investigated for different duration time. For verification of thermochromic performance of VO₂ films optical measurements in UV-Vis-NIR range as a function of temperature were done, while Scanning Electron Microscopy (SEM) was employed to examine the morphology and distribution of VO₂ particles. In particular, the duration of ball-milling process seems to affect the homogeneity of film and consequently increasing the thermochromic ability.