Low-Temperature Topotactic Control of a Double Exchange Interaction in an La_0.5Sr_0.5CoO₃ Oxygen Sponge Facilitates the Development of Ultra-Sensitive and Stable Correlated Oxygen Sensors

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_0.5Sr_0.5CoO₃ 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_0.5Sr_0.5CoO₃, which is further amplified with the topotactic transition into brownmillerite La_0.5Sr_0.5CoO_2.5. This more facile transition is attributable to oxygen-driven filling of correlated electrons in Co 3d-orbitals and successive destabilization of CoO₆ octahedra into CoO₄ tetrahedra. The La_0.5Sr_0.5CoO₃ oxygen sponges with ionic-electric-magnetic coupling constitute a proof-of-principle demonstration that ultra-sensitive and stable oxygen sensors can be achieved.