Thermoelectric properties of Ca_3-xEu_xCo_3.95Ga_0.05O_9+δ (0 ≤ x ≤ 0.10)

Polycrystalline samples of Ca_3–xEu_xCo_3.95Ga_0.05O_9+δ (x = 0.00, 0.02 and 0.10) have been prepared by conventional solid-state synthesis and their thermoelectric properties measured at 25 K to 300 K. The XRD results 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 simultaneously increased with increasing Eu³⁺ content. The total thermal conductivity decreased with increasing Eu³⁺ content. A maximum dimensionless figure of merit of 0.033 at 300 K was reached for Ca_2.9Eu_0.1Co_3.95Ga_0.05O_9+δ, which is about 27 % higher than that of the undoped sample. These results suggest that the Eu is an effective doping element for improving the thermoelectric properties of Ca₃Co_3.95Ga_0.05O_9+δ.