Influence of SiC dispersion and Ba(Sr) substitution on the thermoelectric properties of Ca3Co4O9+δ

Ca3Co4O9+δ is a typical p-type thermoelectric oxide material with a low thermal conductivity. In this study, double-layered oxide samples Ca(Ba,Sr)3Co4O9+δ dispersed with different SiC contents were obtained via the traditional solid phase reaction method. The effects of different elemental substitutions and SiC dispersion contents on the microstructure and thermoelectric properties of the samples were studied. The double optimisation of partial substitution of Ca-site atoms and SiC dispersion considerably improved the thermoelectric properties of Ca3Co4O9+δ. Through the elemental substitution, the resistivity of the Ca3Co4O9+δ material was reduced. Conversely, introducing an appropriate amount of SiC nanoparticles enhanced phonon scattering and was crucial in reducing its thermal conductivity. After double optimisations, the dimensionless thermoelectric figure of merit (ZT) values of both Ca2.93Sr0.07Co4O9+δ + 0.1 wt% SiC and Ca2.9Ba0.1Co4O9+δ + 0.1 wt% SiC achieved an optimum value of 0.25 at 923 K.