Low temperature electrical and thermal transport properties of the Ca3-xSbxCo4O9 system

In this study, the Ca3-xSbxCo4O9 (x = 0.0, 0.5, 0.75 and 1.0) system was fabricated using solid-state reaction technique. From the XRD analysis, it was found that increase of the Sb concentration in the system caused formation of impurity phases and therefore a distortion in the main lattice. The SEM-EDX results showed that the grain size reduced with increasing Sb in the Ca3Co4O9 system. The resistivity, rho, value increased with increasing the Sb-content and insulating behavior was obtained as the temperature was decreased. The samples fabricated have positive thermoelectric power, S, value, suggesting that holes are dominant charge carriers in the samples. S value decreased with decreasing the temperature. The Fermi energy, E-F , and the carrier concentration, n, decreased by the Sb-substitution. The Sb-substitution caused a decrease of thermal conductivity, kappa which is due to reduction of the phonon thermal conductivity, kappa(ph,) in the system. Figure of merit, ZT, value decreased significantly due to strongly increase in rho. The impurities, defects and distortion with substitution of Sb are responsible for large variation on electrical and thermal transport properties.