BaCoO: A Thermoelectric Oxide Showing a Reliable of ∼0.55 at 600 °C in Air.

Thermoelectric energy conversion technology has attracted attention as an energy harvesting technology that converts waste heat into electricity by means of the Seebeck effect. Oxide-based thermoelectric materials that show 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. Although several high- thermoelectric oxides ( > 1) have been reported thus far, the reliability is low due to a lack of careful observation of their stability at elevated temperatures. Here, we show a reliable high- thermoelectric oxide, BaCoO. We fabricated BaCoO epitaxial films by the reactive solid-phase epitaxy method (NaCoO) followed by ion exchange (Na → Ba) treatment and performed thermal annealing of the film at high temperatures and structural and electrical measurements. The crystal structure and electrical resistivity of the BaCoO epitaxial films were found to be maintained up to 600 °C. The power factor gradually increased to ∼1.2 mW m K and the thermal conductivity gradually decreased to ∼1.9 W m K with increasing temperature up to 600 °C. Consequently, the reached ∼0.55 at 600 °C in air.