Improvement of thermoelectric performance in magnetically c-axis-oriented bismuth-based cobaltites

Fabrication of thermoelectric Bi-based cobaltites with large magnetic anisotropy (Δχ = χc − χab) and relatively low resistivity using a crystallochemical process is reported. Doping of various rare earth (RE) ions into the Ca site in [(Bi0.5Pb0.5)2Ca2O4]yCoO2 [(Bi, Pb)Ca222] enhanced Δχ comparable to that of [Ca2CoO3−δ]0.62CoO2. Tailoring of the Sr-doping level in Dy-doped (Bi, Pb)Ca222 enabled the resistivity to be reduced without decreasing Δχ. The magnetically c-axis-oriented (Sr, Dy)-doped (Bi, Pb)Ca222 bulk exhibited improved thermoelectric performance compared with the Sr-free RE-doped BiCa222 and a-axis grain-oriented [(Bi0.5Pb0.5)2Sr2O4]∼0.55 CoO2.