Higherature thermoelectric properties of Ca_0.9-xSr_x Yb_0.1 MnO₃-δ (0x_0.2)

Polycrystalline samples of Ca_0.9-xSr_x Yb _0.1 MnO₃-δ (x=0, 0.025. 0.05, 0.1, and 0.2) were prepared by a conventional solid-state reaction and their thermoelectric properties were evaluated at 303-973 K. Each of the samples consisted of a single phase with an orthorhombic structure. All the samples showed a metallic conductivity and their electrical resistivity was markedly affected by the distortion of the MnO6 octahedron. The Seebeck coefficient of all the samples was negative, indicating that the predominant carriers were electrons over the entire temperature range examined. The highest power factor achieved (0.22 mW m-1 K-2 at 773 K) was shown by the sample with x=0.1. The thermal conductivity was affected by both the crystal distortion and the difference in mass between the Ca2+ and Sr2+ ions. The highest dimensionless figure of merit obtained was 0.09 at 973 K for the sample with x=0.1; this is a result of its low electrical resistivity and its moderate Seebeck coefficient and thermal conductivity.