Oxygen-Valve Formed in Cobaltite-Based Heterostructures by Ionic Liquid and Ferroelectric Dual-Gating

Manipulation of oxygen vacancies via electric-field-controlled ionic liquid gating has been reported in many model systems within the emergent fields of oxide electronics and iontronics. It is then significant to investigate the oxygen vacancy formation/annihilation and migration across an additional ferroelectric layer with ionic liquid gating. Here, we report that via a combination of ionic liquid and ferroelectric gating, the remote control of oxygen vacancies and magnetic phase transition can be achieved in SrCoO_2.5 films capped with an ultrathin ferroelectric BaTiO₃ layer at room temperature. The ultrathin BaTiO₃ layer acts as an atomic oxygen valve and is semitransparent to oxygen-ion transport due to the competing interaction between vertical electron tunneling and ferroelectric polarization plus surface electrochemical changes in itself, thus resulting in the striking emergence of new mixed-phase SrCoO_x. The lateral coexistence of brownmillerite phase SrCoO_2.5 and perovskite phase SrCoO_3-δ was directly observed by transmission electron microscopy. Besides the fundamental significance of long-range interaction in ionic liquid gating, the ability to control the flow of oxygen ions across the heterointerface by the oxygen valve provides a new approach on the atomic scale for designing multistate memories, sensors, and solid-oxide fuel cells.