Topotactic phase transformation in correlated vanadium dioxide through oxygen vacancy ordering

Controlling the insulator-metal transition (IMT) in correlated oxide system through oxygen vacancy ordering opens up a new paradigm for exploring exotic structural transformation and physical functionality. Oxygen vacancy serves as a powerful tuning knob for adjusting the IMT property in VO2, though driving topochemical reduction to V2O3 remains challenging due to structural incompatibility and competing phase instability. Here we unveil consecutive oxygen-vacancy-driven VO2-VO2-x-V2O3 topotactic phase transformation route with enticing facet-dependent anisotropy, engendering tunable IMT properties over an extended temperature range. Remarkably, topochemically reduced V2O3 inherits the crystallographic characteristics from parent VO2, enabling emergent lattice framework and IMT behavior inaccessible via direct epitaxial growth. Analogous electron doping arising from hydrogenation and oxygen vacancy contributes cooperatively to drive the Mott phase transition in VO2 through band-filling control. Our work not only unveils sequential topotactic phase transformations in VO2 through oxygen vacancy ordering but also provides fundamentally new insights for defect-mediated Mott transitions.