Publication date: 15th December 2025
Being able to control how materials exchange and conduct heat could open new avenues of research, generating a novel class of heat-driven devices such as thermal switches and thermal transistors1,3. One of the most promising approaches to build these components is based on the variation of the thermal conductivity of an active layer pumping ions in/out the layer through an electrolyte from/towards a counter electrode. Some examples of such transistors have been developed, usually employing liquid electrolytes2. While variations in thermal conductivity of efficient active layers have been reported, a short variation of conductivities and the inability to be integrated into a circuit have hindered the performance and the applicability of thermal transistors. Solid-state thermal transistors with systems formed by a solid electrolyte and an oxide active layer have recently been studied as a response to these limitations3.
In this work, we study the effect of oxygen stoichiometry on the thermal properties of complex oxides that can change their crystalline structure by reduction/oxidation processes through a solid electrolyte. In particular, we focus on SrFeO3, in which we can produce phase changes from perovskite to brownmillerite in a fully reversible manner. For this purpose, we designed and fabricated a platform to modulate the oxygen stoichiometry of the active layer, producing a wide span of oxygen contents in a single sample. In the first step, a thin film of the active oxide was deposited by PLD on a substrate of yttrium-doped zirconia, which is an ion-conductive oxide, functioning as an electrolyte. Later, we designed and fabricated a gold pad stripe pattern on top of the thin film. Finally, by applying a voltage between this strip and a silver counter electrode, we modified the oxygen stoichiometry along the gold stripe, which was determined using a non-destructive optical-based procedure. Finally, by using the frequency domain thermoreflectance technique we were able to make precise measurements of the thermal conductivity at each point, thus correlating the oxygen content in the film with the thermal conductivity. The studied material shows that there is a lot of potential for this family of oxides in the field of thermal modulation.
This work is part of the project POWERDOT, funded by MCIN/AEI/FEDER with PID2022-142003OB-C21.
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