Synthesis of Ca3Co4O9 ceramics by polymerized complex and hydrothermal hot-pressing processes and the 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. Observation by scanning electron microscope indicated that the form of powders by the PC process was fine and flaky. The density of the sintered body increased with an increase of the operating temperature and pressure during the HHP process. The electrical resistivity was greatly reduced with an increase of the operating pressure, but the thermal conductivity is prone 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 1,073 K.