Misfit-layered oxides Ca3−xLnxCo4O9+ with Ln = Dy, Er, Ho, and Lu were synthesized using solid state reactions. The resulting samples were hot-pressed (HP) at 1123K in air for 2 h under a uniaxial pressure of 60 MPa. Thermoelectric properties of Ca3−xLnxCo4O9+ı 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 1073K for the Ca2.8Lu0.2Co4O9+ sample, which is about 1.6 times larger than that for the non-doped counterpart.
Keyword: Thermoelectric materials; Oxide materials; Solid state reactions; Thermoelectrics