Visible Thermochromism in Vanadium Pentoxide Coatings.

Although di-vanadium pentoxide (VO) has been a candidate of extensive research for over half a century, its intrinsic thermochromism has not been reported so far. Films of VO grown on silicon, glass, and metal substrates by metal organic chemical vapor deposition in this study exhibit a thermally induced perceptible color change from bright yellow to deep orange. Temperature-dependent UV-vis spectroscopy and X-ray diffraction allow the correlation between the reversible continuous red shift of the absorption and the anisotropic thermal expansion along the (001) direction, that is, perpendicular to the sheets constituting the layered structure. Furthermore, the possibility of tuning the thermochromic behavior was demonstrated via a chemical doping with chromium.