Synthesis of Ca3Co4O9 Ceramics by Citric Acid Complex and Hydrothermal Hot-pressing Processes and its Thermoelectric Properties

Ca₃Co₄O₉ ceramics powders were synthesized by the citric acid complex (CAC) method and consolidated by the hydrothermal hot-pressing (HHP) technique. The observation by the scanning electron microscope indicated that the powders obtained by the CAC process show plate-like grains. The density and the Lotgering factor, which was estimated from the X-ray diffraction data, of the sintered body increase with an increase of the operating pressure during the HHP process. The electrical resistivity is much reduced with an increase of the operating pressure, but the Seebeck coefficient was hardly affected by the HHP conditions. As a result, the sample treated by the HHP under the condition of 573 K, 200 MPa and 3 h shows a maximum power factor