The durability study of thermochromic vanadium dioxide films with the addition of barrier coatings

The high-performance thermochromic vanadium dioxide (VO₂) films can be applied in many industrial applications such as smart windows, infrared sensors, and infrared imaging (bolometers). The preservation of its highly thermochromic properties of VO₂ films is crucial since the oxidation number of vanadium ranges from +2 to +5 under various reducing or oxidizing atmospheres at elevated temperatures and humid environment. In this study, VO₂ films were fabricated by thermal oxidation of co-sputtered thin films of vanadium and stainless-steel (SS), followed by the addition of barrier coatings on top of the as-prepared VO₂ films for the improvement of long-term stability. The samples with barrier coatings containing zinc oxide (ZnO) and silicon oxide (SiO₂) showed significantly better durability in either wet or dry high temperature environment. With an equivalent barrier coating thicknesses, the stability of the samples was ranked in the order of TiO₂/ZnO/VO₂:SS ∼ ZnO/SiO₂/VO₂:SS > VO₂:SS > TiO₂/SiO₂/VO₂:SS > Plain VO₂ at wet condition (95% RH, 80 °C). In addition, the durability order was: TiO₂/ZnO/VO₂:SS > ZnO/SiO₂/VO₂:SS ∼ TiO₂/SiO₂/VO₂:SS > VO₂:SS > Plain VO₂ at dry condition (300 °C). The results suggest that the proposed VO₂/TiO₂/ZnO barrier coating is a promising material for both durability and thermochromic performance.