Structure, magnetic and transport properties in Ca3Co4−xSbxO9 ceramics

The structure, magnetic, electrical and thermal transport properties of Ca 3 Co 4− x Sb x O 9 (0 ⩽ x ⩽ 0.2) have been investigated systematically. Base on the analysis of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the valence state of the doped Sb ions is suggested to be +3 in the x = 0.05 sample, and its content increases monotonously along with the gradual introduction of Sb 5+ ions as x further increases. The resistivity and the metal–insulator-transition temperature increase with increasing x , indicating the more stable spin-density-wave state in the Sb-doped samples. The thermopower decreases first as x = 0.05, and then increases monotonously with increasing x till to 0.15. The thermal conductivity decreases obviously due to Sb-doping. As a result, the Ca 3 Co 3.90 Sb 0.10 O 9 sample has the largest thermoelectric figure-of-merit ZT value of 0.012 at room temperature, which is about two times larger than that of Ca 3 Co 4 O 9 . The results are suggested to originate from the variations of carrier concentration and electronic correlation via Sb-doping with the different valence states.