Structural and Thermoelectric Properties of Nanostructured Nominally Stoichiometric Pb1−x Bi x Te Prepared by Mechanical Alloying

We have investigated the influence of substituting bismuth for lead in lead telluride. The material was nanostructured by mechanical alloying and compacted via short-term sintering or hot pressing. Synthesis of samples with substitution up to 6 at.% bismuth was carried out twice to ensure reproducibility. All relevant thermoelectric transport parameters were measured in a wide temperature range from 123 K or 173 K to 773 K. Two different techniques for measuring the electrical conductivity and Seebeck coefficient were used, one at low and the other at high temperature. Higher bismuth content of 4 at.% to 6 at.% was found to result in the best thermoelectric properties, with maximum ZT value of about 0.7 at 723 K for 4.0 at.% bismuth. The structure was examined in detail via x-ray diffraction analysis, Raman spectroscopy, and transmission electron microscopy. A key feature of the microstructure was the inhomogeneous distribution of bismuth in the lead telluride matrix and the occurrence of bismuth-rich regions on the nanoscale, related to remarkably increased carrier concentration and mobility.