Development and evolution of nanostructure in bulk thermoelectric Pb-Te-Sb alloys

Abstract

Motivated by reports of exceptionally high zT > 2 in thin film superlattices or "quantum well" materials with nanometer sized features, we have undertaken a study of composite materials with nanoscale features that promise to provide similar structures in bulk material. Nanometer scale layers of PbTe and Sb_2Te_3 with periodicities of 180 nm to 950 nm form when quenched eutectic PbTe-Sb_2Te_3 melt, crystallizing as Pb_2Sb_6Te_(11), subsequently annealed. The lamellar spacing depends on the temperature and time of the anneal. The mechanism for the development of the nanostructures is probed by examining the fraction of material transformed as a function of anneal time. Preliminary analysis of the shape factor exponent reveals that the transformation to the nanostructured lamellae bears similarities to the thickening of very large plates. The coarsening of the lamellar spacing is also examined as a function of time and temperature.

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