Peeling off single-crystalline thermoelectric oxide films

POINT

• Succeeded in single crystallization of Ba_1/3CoO₂, a high-performance thermoelectric material that is stable at high temperatures and in air.
• Peeling off the Ba_1/3CoO₂ single crystal film fabricated on the sapphire substrate.
• After peeling, the free-standing Ba_1/3CoO₂ single crystal film maintains high thermoelectric performance.

ABSTRACT

A research group led by Professor Hiromichi Ohta of Research Institute for Electronic Science, Hokkaido University has succeeded in single crystallization of Ba_1/3CoO₂, a high-performance thermoelectric material that is stable at high temperatures and in air. 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. The research group 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. They 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. The results of this research have been published in ACS Applied Electronic Materials on Tuesday, October 17, 2023 (JST).

Kungwan Kang, Fumiaki Kato, Akitoshi Nakano, Ichiro Terasaki*, Takashi Endo, Yasutaka Matsuo, Hyoungjeen Jeen*, and Hiromichi Ohta*, “Fabrication and Thermoelectric Properties of Freestanding Ba_1/3CoO₂ Single Crystalline Films”, ACS Appl. Electron. Mater. XXXX, XXX (2023). (DOI: 10.1021/acsaelm.3c01129)