Thermoelectric properties of Ca2.95Bi0.05Co4−xFexO9+δ (0⩽x⩽0.15)

[Display omitted] •The Fe doping element has remarkable effects on the thermoelectric properties of the system.•Resistivity of all the samples exhibits the nonmetallic to metallic transition at below 78K.•Ca2.95Bi0.05Co3.80Fe0.15O9+δ shows the highest dimensionless figure of merit. Polycrystalline samples of Ca2.95Bi0.05Co4−xFexO9+δ (x=0.00, 0.05, 0.10, and 0.15) are prepared by conventional solid-state synthesis. The XRD results show that all the samples are single phase. The thermopower of all the samples is positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity and thermopower decrease with increasing Fe content. Among all the samples, Ca2.95Bi0.05Co3.95Fe0.15O9+δ exhibits the highest dimensionless figure of merit of 0.064 at 300K. These results suggest that the Fe is an effective doping element for improving the thermoelectric properties of Ca2.95Bi0.05Co4O9+δ.