Topotactic Phase Transformation in Vanadium Dioxide through Oxygen Vacancy Ordering with Synergistic Electron Doping via Hydrogenation

Controlling the insulator-metal transition (IMT) in correlated oxide system through oxygen vacancy ordering opens up a new paradigm for unlocking exotic structural transformation and physical functionality. Oxygen vacancies serve as a powerful tuning knob for adjusting the IMT property of VO₂, though driving topochemical reduction to V₂O₃ remains rather challenging due to structural incompatibility and competing phase instability. Here, a consecutive oxygen-vacancy-driven VO₂-VO_2-x-V₂O₃ topotactic phase transformation route is demonstrated with pronounced facet-dependent anisotropy, engendering widely tunable IMT properties across an extended temperature range over 200 K. Remarkably, topochemically reduced V₂O₃ inherits the crystallographic characteristics from parent VO₂, enabling the possibility of accessing exotic lattice framework with tunable IMT behaviors. Analogous electron doping arising from hydrogenation and oxygen vacancies contributes cooperatively to drive Mott phase transition in VO₂ through band-filling control, while ionic interactions between protons and oxygen vacancies markedly accelerate the oxygen ionic mobility. The work not only establishes a framework for engineering physical functionality through defect-mediated topotactic transition and band filling but also provides fundamentally new insights for filling-controlled Mott physics.