Fabrication and Thermoelectric Properties of Freestanding Ba_1/3CoO₂ Single-Crystalline Films

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 1/3 CoO 2 epitaxial films exhibit the highest figures of merit. For the practical use of Ba 1/3 CoO 2, bulk ceramics or single-crystalline Ba 1/3 CoO 2 is necessary. Here, we show that freestanding Ba 1/3 CoO 2 single-crystalline films can be fabricated by peeling Ba 1/3 CoO 2 epitaxial films from the substrate. We fabricated Ba 1/3 CoO 2 epitaxial films and immersed them in 40 °C hot water for several tens of minutes. Subsequently, the Ba 1/3 CoO 2 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 provide a useful method for fabricating freestanding single-crystalline oxide films for thermoelectrics.