A comparative study uncovering the different effect of Nb, Mo and W dopants on phase transition of vanadium dioxide

Vanadium dioxide is a promising material for energy-saving and smart switching applications due to its reversible metal-to-insulator transition (MIT) accompanied by swift changes in electrical and optical properties. However, its deployment in practical applications is utterly restricted due to its high MIT temperature (∼ 68Co) and vague MIT mechanism. Although the MIT temperature can be reduced via high valence cations doping, the cause of diverse effects on MIT temperature by Nb, Mo, and W doping was not well defined. Here, we conducted a systematic study of Nb, Mo, and W dopants in the VO2 host material to understand the nature of the MIT and the contrast in reducing MIT temperature due to these dopants. Poor hybridization of Nb-4d and V-3d states and enhanced Nb–O ionic character due lower electronegativity of Nb was observed in both M1 and R phases which softened V–V interaction. On the other hand, W with high electronegativity was found better than Nb and Mo in contributing localized electrons via strong hybridization of V-3d and dopant states, effecting thermochromic properties strongly. The fundamentals behind the diverse effect on MIT temperature of studied dopants have also been explained. These findings expose the MIT mechanism in VO2 and help to modulate its properties for thermochromic windows and smart switching applications.