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

Misfit-layered oxides Ca(3-x)Ln(x)Co(4)O(9+delta) 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 2h under a uniaxial pressure of 60 MPa. Thermoelectric properties of Ca(3-x)Ln(x)Co(4)O(9+delta) 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 Ln(3+). 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+delta sample, which is about 1.6 times larger than that for the non-doped counterpart. (C) 2010 Elsevier B.V. All rights reserved.