Abstract
NaxCo2O4 powders synthesized by citric acid complex (CAC) process were mechanically milled with Ag particles around 1μm in size and then pressurelessly sintered. Effects of the mechanical milling on microstructure and thermoelectric properties of a NaxCo2O4/Ag composite were investigated. Ag powder was finely dispersed in the NaxCo2O4/Ag mixed powder after mechanical milling. The NaxCo2O4/Ag sintered bodies showed the large crystallographic anisotropy as compared to the NaxCo2O4/Ag composite synthesized by the conventional CAC process. However, Ag particles were coarsened during sintering, and the NaxCo2O4/Ag composite polycrystal with dispersion of fine Ag grains could not be obtained. By Ag addition, the electrical resistivity was significantly reduced, but the thermal conductivity was increased because of the coarse Ag phase, resulting in the dimensionless figure of merit almost the same as, or smaller than, that of the sample without Ag.
