Thermoelectric Performance of Single-Phase Tellurium-Reduced Quaternary (PbTe)(0.55)(PbS)(0.1)(PbSe)(0.35)

Lead chalcogenide quaternary systems have been shown to provide high thermoelectric (TE) efficiency superior to those of binary and ternary lead chalcogenides, arising from both altered electronic band structures and a reduction in lattice thermal conductivity. Here, we have synthesized single-phase samples of the quaternary compound (PbTe)(0.55)(PbS)(0.1)(PbSe)(0.35) doped with Na and characterized their TE properties. We show that the dopant solubility is limited to 1 at. %. A very low lattice thermal conductivity of similar to 0.6 W m(-1) K-1 at 850 K is achieved at all dopant concentrations because of phonon scattering from point defects associated with solute atoms with high contrast atomic mass. As a result, a high TE figure of merit of approximately 1.5 is achieved at 823 K in heavily doped samples. Moreover, the figure of merit is greater than 1 over a wide temperature range above 675 K.