Phase transition in thermochromic VO2 coatings grown by ac dual magnetron cathode sputtering

High quality of thermochromic VO 2 coatings were grown onto ITO-coated quartz by thermal oxidation of ac magnetron sputtered vanadium oxide films. The thermochromic properties of VO 2 coatings were investigated by means of IR transmittance and Raman scattering measurements as a function of temperature (up to 100 °C). It is observed that the IR transmittance of VO 2 decreased by increasing temperature, that is the signature of the semiconductor-to-metallic transition (SMT). The associated transition temperature was found to be around 56 °C. At room temperature, the Raman analysis showed only the presence of vibrational modes of the pure VO 2 phase. However, the temperature dependent Raman measurements showed that the scattered signals decreased by increasing the temperature and they disappeared completely when the VO 2 switched to its metallic state. The structural phase transition from a monoclinic crystalline structure (at room temperature) to a tetragonal rutile type structure (at high temperature) appeared at relatively high temperature (~ 75 °C) compared to the SMT transition temperature (~ 56 °C). The evolution of vibrational Raman modes in the heating and cooling cycles showed relatively large hysteresis (~ 10 °C).