Thermoelectric energy conversion has attracted attention as an energy-harvesting technology for converting waste heat into electricity via the Seebeck effect. Conducting oxide-based thermoelectric materials that exhibit a high figure of merit are promising because of their good chemical and thermal stability, as well as their harmless nature compared to chalcogenide-based state-of-the-art thermoelectric materials. Among many conducting oxides, Ba_1/3CoO₂ epitaxial films exhibit the highest figures of merit. For the practical use of Ba_1/3CoO₂, bulk ceramics or single-crystalline Ba_1/3CoO₂ are necessary. Here, we show that freestanding Ba_1/3CoO₂ single-crystalline films can be fabricated by peeling Ba_1/3CoO₂ epitaxial films from the substrate. We fabricated Ba_1/3CoO₂ epitaxial films and immersed them in 40 °C hot water for several tens of minutes. Subsequently, the Ba_1/3CoO₂ epitaxial film spontaneously peeled off and floated on the surface of the water like seaweed. We measured and analyzed the crystal structure, chemical composition, and thermoelectric properties before and after peeling and realized that there was no significant difference. The present results would provide a useful method for fabricating freestanding single-crystalline oxide films for thermoelectrics.

Reference movie (Peeling off of Na_0.75CoO₂ single crystalline film) Reference Adv. Mater. 18, 1649–1652 (2006).