Effect of Composition on Thermoelectric Properties in PbTe-Bi2Te3 Composites

The solidification of alloys in the Bi2Te3-PbTe pseudobinary system at off- and near-eutectic compositions was investigated for their microstructure and thermoelectric properties. Dendritic and lamellar structures were clearly observed due to the phase separation and the existence of a metastable ternary phase. In this system, three phases with different compositions were observed: binary Bi2Te3, PbTe, and metastable PbBi2Te4. The Seebeck coefficient, electrical resistivity, and thermal conductivity of ternary alloys as well as binary compounds were measured. The phonon thermal conductivities of Pb-Bi-Te alloys were lower than those in binary PbTe and Bi2Te3, which could have resulted from the increased interfacial area between phases due to the existence of the metastable ternary phase and the resultant phase separation.