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Increased Seebeck Coefficient and Decreased Lattice Thermal Conductivity in Grain-Size-Controlled p-Type PbTe–MgTe System

PbTe systems are known as good thermoelectric materials for midtemperature range applications. Here, we demonstrate that a method of melt-spinning followed by pulsed electric current sintering is effective to synthesize nanostructured bulk PbTe with enhanced thermoelectric properties. The bulk samples with the nominal composition PbTe–2% MgTe doped with 4% Na consist of a hierarchical nanostructure, where MgTe-based nanoprecipitates with the size of ∼2–15 nm exist in the PbTe grains that are several hundred nm in size. Both the nanoscale precipitates and the high-density grain boundaries effectively scatter heat-carrying phonons, leading to significant reduction in the lattice thermal conductivity. Furthermore, an increased Seebeck coefficient is observed, which can be explained by band convergence induced by alloying Mg and energy filtering induced by grain boundaries. The simultaneous realization of the decreased lattice thermal conductivity and increased Seebeck coefficient results in the enhanced ther...