Thermoelectric properties of Tl–X–Te (X=Ge, Sn, and Pb) compounds with low lattice thermal conductivity

We prepared polycrystalline-sintered samples of Tl2GeTe3, Tl4SnTe3, and Tl4PbTe3 and evaluated their thermoelectric properties. Although the electrical properties of these compounds were not optimized, the dimensionless figure of merit ZT was relatively high, i.e., 0.74 at 673K for Tl4SnTe3, 0.71 at 673K for Tl4PbTe3, and 0.29 at 473K for Tl2GeTe3, due to the very low lattice thermal conductivity of the compounds. Low lattice thermal conductivity appears to be closely related to the weak bonding of atoms and complex crystal structures of these compounds.