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 films capped with an ultrathin ferroelectric BaTiO layer at room temperature. The ultrathin BaTiO layer acts as an atomic oxygen valve and is semitransparent to oxygen ions 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 SrCoOx mixed-phase. The lateral coexistence of brownmillerite phase SrCoO and perovskite phase SrCoO 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 at the atomic scale for designing multi-state memories, sensors, and solid-oxide fuel cells.