Spectroscopic evidence for directional oxygen-ion transport in correlated oxide heterostructures with tunable migration dynamics

Abstract

Oxygen chemical potential mismatch (Δµ_O) spontaneously drives directional ionic transfer across oxide heterointerfaces, offering a facile route to introduce oxygen deficiencies beyond the traditional thermal stimulus in monolayer materials. Here, we provide compelling spectroscopic evidence for directional oxygen-ion transport in a TiO₂/VO₂ heterostructure, driven by a built-in Δµ_O gradient, uncovering critically balanced Peierls–Mott physics. Given the exceptional sensitivity of VO₂ to external stimuli, the band filling in the t_2g band of VO₂, together with the suppression of V–V dimerization, is clarified using synchrotron and Raman spectroscopy techniques, circumventing artifacts typically introduced by electron-beam illumination. Oxygen off-stoichiometry in the TiO₂ overlayer functionalized as an oxygen reservoir is identified as a powerful tuning knob for actively accelerating ionic transport dynamics. By harnessing the symmetry mismatch between VO₂ and Al₂O₃, either the inclined or vertically aligned domain-boundary configuration achieved in VO₂ can offer an efficient pathway for oxygen-ion diffusion, extending the horizons of material design for iontronic devices. Our findings establish a feasible strategy to controllably manipulate oxygen-ion transport in oxide heterostructures, driven by the Δµ_O gradient, while offering direct spectroscopic evidence that deepens the understanding of defect-associated correlated physics.