High-temperature thermoelectric properties of late rare earth-doped Ca3Co4O9+δ

Misfit-layered oxides Ca3−xLnxCo4O9+δ with Ln = Dy, Er, Ho, and Lu were synthesized using solid state reactions. The resulting samples were hot-pressed (HP) at 1123 K in air for 2 h under a uniaxial pressure of 60 MPa. Thermoelectric properties of Ca3−xLnxCo4O9+δ were investigated up to 1200 K. Both the Seebeck coefficient and electrical resistivity increase upon Ln substitution for Ca. Among the Ln-doped samples, the magnitude of Seebeck coefficient tends to increase with decreasing ionic radius of Ln3+. The Ln-doped samples exhibit a lower thermal conductivity than the non-doped one due to a decrease of their lattice thermal conductivity. The dimensionless figure of merit, ZT, reaches 0.36 at 1073 K for the Ca2.8Lu0.2Co4O9+δ sample, which is about 1.6 times larger than that for the non-doped counterpart.

. Temperature dependence of the thermal conductivity (a) and dimensionless figure of merit, ZT; (b) for non-doped, Ca2.9Ln0.1Co4O9+δ (Ln = Ho and Lu), and Lu-doped with x = 0.2 samples. The dimensionless figure of merit, ZT, reaches 0.36 at 1073 K for the Ca2.8Lu0.2Co4O9+δsample.Figure optionsDownload as PowerPoint slideResearch highlights▶ Misfit-layered oxides Ca3−xLnxCo4O9+δwith Ln = Dy, Er, Ho, and Lu were synthesized by the solid state reaction followed by hot-pressing. Thermoelectric properties were investigated up to 1200 K. ▶ Among the Ln-doped samples, the magnitude of Seebeck coefficient tends to increase with decreasing ionic radius of Ln3+. The Ln-doped samples exhibit lower thermal conductivity than the non-doped one due to a decrease of their lattice thermal conductivity. ▶ The dimensionless figure of merit, ZT, reaches 0.36 at 1073 K for the Ca2.8Lu0.2Co4O9+δsample, which is about 1.6 times larger than that for the non-doped counterpart.