[12p-S203-1~13] 6.3 Oxide electronics

▼ [12p-S203-10] High-Temperature Thermoelectric Figure of Merit of Ba_1/3CoO₂ Epitaxial Films

〇(P)Xi Zhang¹, Yuqiao Zhang¹, Liao Wu², Hai Jun Cho¹, Hiromichi Ohta¹ (1.RIES Hokkaido Univ., 2.IST Hokkaido Univ.)

Keywords:Layered cobaltite, Thermoelectric, Low thermal conductivity

Thermoelectric materials, which can convert wasted heat exhausted in our daily life into electricity, have become promising candidates to meet the challenges of global energy issues. Layered cobalt oxides such as Na_3/4CoO₂ and Ca₃Co₄O₉ are attracting increasing attention as potential p-type thermoelectric materials due to their promising thermoelectric properties and environmental compatibility. However, the ZT of layered cobalt oxides is lower compared to heavy metal-based chalcogenides like Bi₂Te₃ and PbTe, mainly due to their high thermal conductivity. In this regard, we hypothesized that the thermal conductivity of layered cobalt oxides can be reduced by heavier ion substitution. Recently, we found Ba_1/3CoO₂ films exhibit a high ZT of 0.11 at room temperature, which arouse our interest to investigate the high-temperature performance of them. In this study, we investigated the thermoelectric properties of the Ba_1/3CoO₂ epitaxial films at elevated temperatures. The films are stable in air with a limitation temperature of up to ~600 °C, which is higher than the thermal stability temperature of Na_3/4CoO₂ (~350 °C). The power factor of Ba_1/3CoO₂ films is similar to Na_3/4CoO₂ films above room temperature with a value of ~1 mW m⁻¹ K⁻². The thermal conductivity of Ba_1/3CoO₂ films at room temperature is ~3 W m⁻¹ K⁻¹, much lower than Na3/4CoO2 films (~5.5 W m⁻¹ K⁻¹), and it greatly decreased to ~1.7 W m⁻¹ K⁻¹ at 573K. As a result, a high ZT of ~0.33 at 573K was achieved, which is the highest among oxide thermoelectric materials.