Bi doping effect on the thermoelectric properties of perovskite-type Sr0.7Ba0.3PbO3

Ceramics of perovskite-type solid solutions Sr0.7Ba0.3Pb1−xBixO3 with x=0.00–0.25x=0.00–0.25 were prepared, and the electrical conductivity and Seebeck coefficient were measured in a temperature range 373–1073 K to elucidate the Bi doping effect on the thermoelectric properties of the Sr0.7Ba0.3PbO3, which was an nn-type semi-metal. The itinerant conduction behavior was observed for the materials with 0.00≤x≤0.100.00≤x≤0.10, in which the Bi atoms were doped as Bi4+ to give electron carriers and mixing of Bi6s orbitals to the conduction band composed of Pb6s–O2p anti-bonding orbitals. The materials changed from semi-metals for x≤0.05x≤0.05 to a metal for x=0.10x=0.10 upon the electron doping. The localized conduction behavior occurred and enlarged with increasing Bi content for the materials with 0.15≤x≤0.250.15≤x≤0.25. This change from itinerant to localized was probably ascribed to the Bi disproportionation from Bi4+ to Bi4+δ and Bi4−δ beyond x=0.10x=0.10, which enlarged with increasing Bi content. Thermoelectric power factors decreased with the Bi doping, mainly due to the large decrease in the absolute values of the Seebeck coefficient, and were maximized for the Bi-undoped Sr0.7Ba0.3PbO3 showing 1.7×10−4 to 3.9×10−4 W m−1 K−2.