Synthesis of Ca3Co4O9 ceramics by polymerized complex and hydrothermal hot-pressing processes and investigation of its thermoelectric properties

Ca₃Co₄O₉ ceramic powders were synthesized by the polymerized complex (PC) method and consolidated by the hydrothermal hot-pressing (HHP) technique. The observation by the scanning electron microscope indicated that the powders by the PC process showed fine and flaky grains. The density of the sintered body increased with an increase of the operating temperature, pressure and time during the HHP process. The electrical resistivity was much reduced with an increase of the operating pressure, but the thermal conductivity is apt to increase with an increase of the operating temperature and pressure. The Seebeck coefficient was hardly affected by the HHP condition. As a result, the sample treated by the HHP process under the condition of 573 K, 200 MPa and 1 h showed a maximum ZT of about 0.29 at 1073 K.