First-principles study of the effect of oxygen vacancy and strain on the phase transition temperature of VO2

Abstract

Vanadium dioxide (VO₂) has been extensively studied as a thermochromic material due to its metal–insulator transition at a critical temperature (T_c) of ∼340 K. Our first-principles calculations show that V–V chains in rutile VO₂ with oxygen vacancy (VO_2−x(R)) exhibit dimerization, and the band gap of monoclinic VO₂ with oxygen vacancy (VO_2−x(M)) can be narrowed to 0.51 eV compared to the 0.69 eV of pure monoclinic VO₂ (VO₂(M)), resulting in increased near-IR absorption. Furthermore, the smaller energy barrier of oxygen vacancy in VO_2−x(M) (0.51 eV) with respect to VO_2−x(R) (0.55 eV) indicates that VO_2−x(M) could easily capture the oxygen from air and transition back to the normal VO₂(M). However, precisely the opposite case is found for VO_2−x(R), such that an oxygen vacancy in VO_2−x(R) can stabilize the rutile phase at a low temperature. In addition, VO_2−x is more sensitive to strain than pure VO₂, implying that combining the effect of the oxygen vacancy and compressive strain could effectively tune the phase transition behavior and further reduce its phase transition temperatures. These results provide a theoretical guidance for the improvement of smart devices.