Molybdenum-doped vanadium dioxide coatings on glass produced by the aqueous sol–gel method

Abstract Thin films of vanadium dioxide (VO2) on glass substrates were produced by the aqueous sol–gel method. Various levels of doping were achieved by adding small quantities of a water-soluble molybdenum compound to the sol. After dip coating, the substrates were reduced by heat treatment in a low-pressure carbon monoxide/carbon dioxide (CO/CO2) atmosphere. The change in electrical conductivity with temperature, and optical reflectance in the semiconductor and metallic phases were measured and compared to undoped VO2 films. Doping the VO2 films with molybdenum lowered the transition temperature of the semiconductor-to-metal phase change; at a doping level of 7 at.% the transition temperature was measured at 24 °C, as indicated by the electrical conductivity. All the films showed a substantial change in reflectance upon heating through the transition. The optical reflectance in the semiconductor state increased slightly with additional dopant, while the reflectance in the metallic state remained constant.