High thermoelectric figure of merit and improved mechanical properties in melt quenched PbTe–Ge and PbTe–Ge1−xSix eutectic and hypereutectic composites

We report the synthesis, microstructure, and transport properties of composite thermoelectric materials based on the eutectic phase relationship between PbTe and Ge. When quenched, these eutectic mixtures exhibit considerably stronger mechanical strength and reduced brittleness compared to PbTe itself, while at the same time they possess lower lattice thermal conductivity. Thermal conductivity measurements show values lower than expected based on the law of mixtures and multiphase composites. We find that the thermoelectric performance in these composites can be tuned through the use of hypereutectic compositions and alloying of Ge with Si. PbI2 was used as an n-type dopant, and precise control of the carrier concentration was achieved to optimize the electrical transport and thermoelectric properties. ZT values approaching 1.3 at 778 K have been obtained in samples of PbTe–Ge0.8Si0.2(5%), which represent an ∼62% improvement over that of PbTe.