open access

https://hdl.handle.net/2115/83799

Layered cobalt oxide epitaxial films exhibiting thermoelectric ZT = 0.11 at room temperature

英語

2021-01-07

Royal Society of Chemistry

Journal of Materials Chemistry A

9(1)

274-280

Among many thermoelectric materials, oxide-based materials draw significant interest due to their environmental compatibility. In particular, layered cobaltite, Na0.75CoO2, shows a large thermoelectric power factor parallel to the layers. However, the thermal conductivity (k) is rather high (5-7 W m(-1) K-1), and therefore, its thermoelectric figure of merit ZT is small (similar to 0.03) at room temperature. Here we show that substituting the Na+ ion with the Ba2+ ion in NaxCoO2 drastically reduces the kappa while keeping the large power factor, resulting in a large enhancement in ZT. We fabricated epitaxial films of Na0.75CoO2 by the reactive solid-phase epitaxy method and performed ion-exchange treatment from Na+ to Ba2+ to synthesize Ba0.27CoO2 films. The room temperature electrical conductivity (s), thermopower (S), and power factor of the c-axis oriented Ba0.27CoO2 films along the in-plane direction were 2310 S cm(-1), +72 mV K-1, and 1.2 mW m(-1) K-2, respectively, while the k along the in-plane, which was clarified by measuring the k of the c-axis inclined (55 degrees) film, was 3.3 W m(-1) K-1. This yields a ZT (= S-2 sigma T/kappa) value along the in-plane as high as 0.11 at room temperature, which is the highest among those reported for oxide thermoelectric materials except oxychalcogenide (BiO)(CuSe).

学術雑誌論文

Accepted Manuscript

2050-7488