Electrochemical Switching of Heat, Charge, and Light in an Oxygen-Sponge Cobaltite, PrBaCo2O5+ x

Abstract

Active control of heat transport in solids is a long-standing challenge for thermal management and phononic technologies. Materials capable of reversibly altering their crystal structures through oxygen exchange provide a promising route to dynamically tune multiple physical properties. Here, we demonstrate electrochemically driven switching of optical, electrical, and thermal properties in epitaxial films of the oxygen-sponge cobaltite PrBaCo2O5+x. This topotactic oxide accommodates large and reversible changes in oxygen content, enabling structural transformations between reduced and oxidized states. X-ray absorption and optical spectroscopy reveal that the Co valence state can be reversibly tuned between +2/+3 and +3/+4 via thermal and electrochemical redox reactions. These transformations induce dramatic changes in physical properties: the electrical resistivity varies by 6 orders of magnitude, from ∼104 Ω cm in the reduced state to ∼10–2 Ω cm in the oxidized state, while the thermal conductivity switches from ∼0.8 to ∼2.7 W m–1 K–1, corresponding to a modulation ratio of ∼3.4. Because the electronic contribution to heat transport is negligible, the thermal switching originates from oxygen-driven structural transformations that modify phonon transport. Our results establish oxygen-sponge cobaltites as a material platform for electrochemically programmable control of heat, charge, and light, opening an opportunity for solid-state thermal switches and adaptive thermal-management technologies.