Low‐Temperature Topotactic Control of a Double Exchange Interaction in an La _0.5 Sr _0.5 CoO ₃ Oxygen Sponge Facilitates the Development of Ultra‐Sensitive and Stable Correlated Oxygen Sensors

Abstract Exotic oxygen‐driven control of quantum‐mechanical properties has attracted considerable attention for the oxygen sensors since it can give superior sensitivity to conventional sensors. Here, it is shown that La _0.5 Sr _0.5 CoO ₃ oxygen sponges simultaneously exhibit a huge change of resistance by three orders of magnitude, a reversible modulation of ferromagnetic ordering, stability, and reusability when the films in vacuum and oxygen is successively annealed. The correlated oxygen sensors work at lower temperatures (175−250 °C) and within a shorter timeframe (8−30 minutes) compared with conventional oxygen sensors working above 500 °C. The oxygen‐driven control starts softly via oxygen‐vacancy‐driven relaxation of double exchange interaction in the perovskite La _0.5 Sr _0.5 CoO ₃ , which is further amplified with the topotactic transition into brownmillerite La _0.5 Sr _0.5 CoO _2.5 . This more facile transition is attributable to oxygen‐driven filling of correlated electrons in Co 3 d ‐orbitals and successive destabilization of CoO ₆ octahedra into CoO ₄ tetrahedra. The La _0.5 Sr _0.5 CoO ₃ oxygen sponges with ionic‐electric‐magnetic coupling constitute a proof‐of‐principle demonstration that ultra‐sensitive and stable oxygen sensors can be achieved.