Influence of ionic sizes of rare earths on thermoelectric properties of perovskite-type rare earth cobalt oxides RCoO3 (R = Pr, Nd, Tb, Dy)

Perovskite-type rare earth cobalt oxide RCoO3 (R = Pr, Nd, Tb, Dy) ceramics were prepared by reaction sintering of corresponding metal oxide powders, and their thermoelectric performances were evaluated up to 873 K. The electrical conductivity of RCoO3 increased with increasing temperature while the Seebeck coefficient decreased, which was a typical semiconducting characteristic. The conductivity and the Seebeck coefficient also depend on the ionic radii of the rare earth cations. The former decreased while the latter increased with decreasing ionic radii. Thermal conductivity of RCoO3 decreased up to certain temperatures and then increased again. The increase above the temperature at which the thermal conductivity reached the minimum value was considered due to the contribution of carrier component on phonon conduction in the present RCoO3 Systems. Thermal conductivity of RCoO3 decreased with increasing temperature, and at same temperature it increased with decreasing ionic radii of the rare earth elements on the low-temperature side. On the other hand, on the high-temperature side, these dependencies were completely opposite. The figure of merit (Z) of RCoO3 increased with increasing temperature up to 673 K and then decreased for NdCoO3 and PrCoO3, while the Z value of DyCoO3 still increased. TbCoO3 and DyCoO3 showed the highest dimensionless figure of merit, ZT = 0.05 at 873 K in the present RCoO3 systems. (C) 2009 Elsevier B.V. All rights reserved.