A comparative study of the thermochromic performances of VO2 films obtained by air oxidation of V and VN precursors

Thanks to its metal-to-insulator transition (MIT) temperature not so far from the ambient one, thermochromic VO2 exhibits great potentiality in smart coatings devoted to energy purposes. Among the different methods to synthesize thermochromic VO2 films, reactive magnetron sputtering remains one of the most suitable for cost-effective industrial-scale production. For a few decades, increasing attention has been paid to a fast and relatively simple approach based on two steps to produce thermochromic VO2 thin films: synthesis of a vanadium thin film followed by its oxidation at moderate temperatures. Recently, we have revealed that the oxidation of vanadium nitride (VN) thin films also gives rise to the formation of thermochromic VO2. This work aims to compare the thermochromic properties of VO2 films achieved after thermal air oxidation of V and VN thin films. For both precursors, short-time air annealing was performed at 550 °C. X-ray diffraction and Raman spectroscopy depicted that the thermal oxidation domain allowing the formation of the thermochromic VO2 phase was enlarged for VN compared to V precursor films. These results were confirmed by electrical measurements. Finally, a particular focus was made on the oxides of the VN series in terms of their infrared properties. The results indicate that the oxidation of VN precursor allows the synthesis of VO2 films with high purity displaying good thermochromic performances (IR contrast of 63%, electrical switch of ∼2 decades) with narrower hysteresis widths (<9.3 °C) as compared to those from vanadium films, making VN precursor of particular interest for industrial upscaling.