Extremely Low Thermal Conductivity in Thermoelectric Ge0.55Pb0.45Te Solid Solutions via Se Substitution

In this contribution, we report that an extremely low lattice thermal conductivity can be achieved in a Ge0.55Pb0.45Te-based thermoelectric system through gradually replacing Te by Se. It was revealed that substitution of Se promotes the solid solubility of Pb in GeTe, hence leading to a reduction of PbTe precipitation. The PbTe precipitation was found to completely disappear when 60% of the Te was replaced by Se. In, the optimized composition alloy (x = 0.5), the substantial percentage of solute Pb and Se atoms in the GeTe-based phase, together with the twinning microstructures in the GeTe-based matrix phase, enhances phonon scattering sufficiently, leading to extremely low thermal conductivities (0.67 and 0.45 W m(-1) K-1 at at 300 and 723 K, respectively), which are the lowest ever reported. The maximum ZT of 1.55 at 723 K was obtained in the alloy Ge0.55Pb0.45Te0.5Se0.5, which is 8 times higher than that of its Se free counterpart Ge0.55Pb0.45Te.