Electrode Oxygen Exchange Enables Polarity-Controlled Resistive Switching in Topotactic SrCoO_2.5

Resistive switching in SrCoO_2.5 has been variably attributed to localized filamentary conduction and lattice-scale oxygen redox; as a topotactic oxide capable of reversible oxygen exchange with minimal lattice disruption, it provides a model system to resolve this distinction, which is critical because the underlying mechanism governs switching stability, reproducibility, and device design. Here, we address this issue by directly comparing Au/SrCoO_2.5/Nb-SrTiO₃ and SrRuO₃/SrCoO_2.5/Nb-SrTiO₃ heterostructures using electrical transport measurements combined with operando bias-dependent x-ray absorption and hard x-ray photoelectron spectroscopy, providing direct sensitivity to lattice-oxygen-driven redox processes. Devices with an oxygen-inert Au electrode exhibit polarity-restricted switching, whereas the oxygen-active SrRuO₃ electrode exhibits switching under both bias polarities within the investigated voltage window, consistent with participation of both interfaces in the bias-induced redox response. Operando spectroscopy reveals electrode-dependent modulation of the Co valence, while complementary structural and vibrational measurements show no macroscopic lattice change but clear local rearrangements of the oxygen coordination, indicating an interface-controlled, spatially distributed redox mechanism. These results identify electrode oxygen-exchange capability as an important parameter governing switching polarity and redox dynamics in topotactic transition-metal oxides. The combined electrical and spectroscopic observations further support the contribution of a distributed redox mechanism to the switching process.