High-temperature thermoelectric properties of Ca3Co4O9+δ with Eu substitution

We have prepared polycrystalline Ca3−xEuxCo4O9+δ (x=0, 0.15, 0.3 and 0.45) samples using a sol-gel process followed by SPS sintering and investigated the Eu substitution effects on their high-temperature thermoelectric properties. With the Eu substitution, both the electrical resistivity and thermopower increase monotonously. This could be attributed to the decrease of hole concentrations by substitution of trivalent Eu3+ for divalent Ca2+. The Eu substituted samples (x=0.15, x=0.3) have lower thermal conductivity than Ca3Co4O9+δ due to their lower electronic and lattice thermal conductivity. The dimensionless figure of merit ZT reaches 0.3 at 1000 K for the sample of Ca2.7Eu0.3Co4O9+δ.