Improvement on the low-temperature thermoelectric characteristics of Ca_3-xYb_xCo₄O_9+δ (0≤x≤0.10)

The effect of ytterbium doping on the low-temperature (<300 K) thermoelectric properties of Ca_3-xYb_xCo₄O _9+δ (x=0.00, 0.02, 0.05 and 0.10) have been investigated. The samples were prepared by conventional solid-state synthesis and their properties measured from 25 K to 300 K. The X-ray diffraction patterns revealed that all the samples are single phase. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity and thermopower were increased and total thermal conductivity was decreased with an increase in ytterbium doping level. Among the doped samples, Ca_2.95Yb_0.05Co₄O _9+δ had the highest dimensionless figure of merit of 0.037 at 300 K, representing an improvement of about 48% compared to the undoped Ca ₃Co₄O_9+δ sample at the same temperature. These results indicate that the partial substitution of Yb³⁺ ion improves the thermoelectric properties of Ca₃Co₄O _9+δ.