Post-calcination, a novel method to synthesize cobalt oxide-based thermoelectric materials

Abstract Cobalt oxide-based Ca 3 Co 4 O 9 ceramics are known for their good thermoelectric (TE) performance and chemical stability at high temperatures ( 3 Co 4 O 9 ceramics is investigated by high-temperature X-ray diffraction analysis. The post-calcination method, which includes cooling and reheating of the phase decomposed Ca 3 Co 4 O 9 ceramics, synthesizes high-density (relative density = 92%) and single-phase Ca 3 Co 4 O 9 ceramics via a solid-state reaction at a high sintering temperature of 1200 °C, and improved TE properties (power factor = 0.245 mW K −2  m −1 at 800 °C) are observed. The post-calcination method is expected to be applicable to Ca 3 Co 4 O 9 and other materials that are difficult to obtain in high-density form due to thermal decomposition. Furthermore, this technique improves the sinterability and production efficiency without using complicated processes.