Fabrication and thermoelectric properties of Ca₃Co₄O₉/Ag composites

Ca₃Co₄O₉/Ag thermoelectric composites were fabricated by hot-pressing the composite powders prepared by a solution chemical process. No second phases or unwanted reaction phase were found in Ca₃Co₄O₉/Ag composites. SEM micrographs revealed that composites exhibited a textured structure and the Ag particles with ∼0.1 to several μm in size distributed at Ca₃Co₄O₉ grain boundaries. Addition of Ag particles has a strong influence on densification and texture development in Ca₃Co₄O₉/Ag composites. By adding Ag particles, the Seebeck coefficient (S) and electrical resistivity (ρ) of composites decrease simultaneously. The power factor (P) of Ca₃Co₄O₉/Ag is found to be improved due to the remarkable reduction in ρ. However, the value decreases when the Ag content is above 7.5 vol.% because the value of S is obviously deteriorated by the presence of large amounts of Ag particles.