IV-VI Compounds for medium temperatures

Lead chalcogenides are traditional thermoelectric materials with decent ZT values. Both PbTe and PbSe have intrinsic two valence bands contributing to high hole DOSs and high Seebeck coefficients. Resonant states could be created in p-type PbTe by Tl doping and n-type PbSe by Al doping to increase the DOSs close to the Fermi levels and Seebeck coefficients. Compared with PbTe and PbSe, PbS is also an ideal candidate because of the cheaper and more abundant S despite the single valence band and absence of the resonant states. Now, it has been easy to obtain high ZTs > 1 in all p-type and n-type PbTe, PbSe, and PbS.1, 2, Since PbTe, PbSe, and PbS have similar face-centered cubic rock salt structure, ternary and quaternary Pb chalcogenides are considered for further optimization. There are always related reports with high ZTs > 2 in the lead chalcogenide samples with different content of Te, Se, and S.16-18 Both PbTe_1-x Se_x and PbSe_1-x S_x are complete solid solution in the whole composition range. PbTe-PbS and PbTe_1-xSe_x -PbS (or PbTe-PbSe_1-xS_x) show very limited solubility. There is a miscibility gap in the phase diagram. In this chapter, we will review the high-performance lead chalcogenides and analyze the reason for the high performance with the categories of PbTe_1-xSe_x, PbSe_1-xS_x, PbTe_1-xS_x, and PbTe_1-x-y Se_xS_y.