Thermochromic vanadium dioxide (VO 2) window coatings hold the promise of reducing the energy consumption of the built environment by passively regulating solar heat gain in response to changing conditions. Composite materials with embedded VO 2 particles have shown greatly improved optical performances compared with thin films, however they typically exhibit broadened phase transition hysteresis and gradient widths, which negatively impacts the overall performance. Here, we present a scalable one-step solution based synthesis for a thermochromic smart window coating based on a vanadium dioxide sol-gel containing silica (SiO 2 nanoparticles. We compare the performance of our nanoparticle composite with thin film VO 2 along with composites formed by mixing VO 2 and SiO 2 sol-gels and find that both composites achieve an acceptable visible transmittance (∼ 50 %) along with a comparable and competitive solar modulation (12.5 % and 16.8 % respectively), roughly double that of the plain VO 2 film (6.7 %). However, our SiO 2 nanoparticle containing composite also benefits from a narrow transition hysteresis and gradient width (9.4 • C and 2.9 • C respectively). We predict that

The first direct synthesis of pure thermochromic VO2(M) nanoparticles with particle sizes below 50 nm by continuous hydrothermal flow synthesis (CHFS).

Monoclinic vanadium(IV) oxide (VO 2 ) has been widely studied for energy-efficient glazing applications because of its thermochromic properties, displaying a large change in transmission of near-IR wavelengths between the hot and cold states. The optimization of the reaction between VCl 4 and ethyl acetate via atmospheric-pressure chemical vapor deposition (APCVD) was shown to produce thin films of monoclinic VO 2 with excellent thermochromic properties (Δ T sol = 12%). The tailoring of the thermochromic and visible light transmission was shown to be possible by altering the density and morphology of the deposited films. The films were characterized by X-ray diffraction, atomic-force microscopy, scanning electron microscopy, ellipsometry, and UV–vis spectrometry. This article provides useful design rules for the synthesis of high-quality VO 2 thin films by APCVD.

Vanadium(IV) oxide thin films were synthesised via Atmospheric Pressure Chemical Vapour Deposition by the reaction between vanadium(IV) chloride and ethyl acetate at 550 °C. The substrate was varied with films being deposited on glass, SnO2 and F-doped SnO2. The films were characterised by X-ray diffraction, X-ray photoelectron spectroscopy, UV/vis spectroscopy, scanning electron microscopy and X-ray absorption near-edge structure. The influence of the electronic contribution of the substrate on the deposited VO2 film was found to be key to the functional properties observed.Highly electron withdrawing substituents, such as fluorine, favoured the formation of V 5+ ions in the crystal lattice and so reduced the thermochromic properties. By considering both the structural and electronic contributions of the substrate, it is possible to establish the best substrate choices for the desired functional properties of the VO2 thin films synthesised.