Enhanced Thermoelectric Properties of Ca(3−x)Ag(x)Co(4)O(9) by the Sol–Gel Method with Spontaneous Combustion and Cold Isostatic Pressing

In this study, Ca(3−x)Ag(x)Co(4)O(9) ceramics were synthesized by the sol–gel method combined with spontaneous combustion and cold isostatic pressing. The Ca(3−x)Ag(x)Co(4)O(9) ceramics were characterized via X-ray diffraction and scanning electron microscopy. Thermoelectric properties of the ceramics were measured from 323 to 673 K. The results indicated that Ag doping significantly affected the microstructure and thermoelectric properties. With the increase in Ag content and gradual increase in electrical conductivity, the Seebeck coefficient first increased and then decreased, whereas the thermal conductivity exhibited the opposite case. The figure of merit, ZT, was 0.17 at 673 K for the Ca(2.8)Ag(0.2)Co(4)O(9) sample. These results indicated that the thermoelectric properties could be optimized remarkably with the substitution of Ag.