Formation of Sb2Te3 Widmanstatten precipitates in thermoelectric PbTe

Unidirectional solidification experiments have been performed with a thermoelectric alloy with a starting composition of Pb10.5Sb31.6Te57.9 in the pseudobinary PbTe-Sb2Te3 system. The bottom of the resulting rod consists of PbTe phase with Widmanstatten precipitates of Sb2Te3. The precipitation is due to a decrease in the solubility of Sb2Te3 with temperature: the solubility at 450 degrees C was determined to be 2.1 +/- 0.2 at.% Sb. The average thickness of plates was estimated to be similar to 100 nm. The spacings between neighboring plates has a distribution in the 200-3000 nm range, peaking around 900 nm. The habit planes of precipitation are of the {1 1 1}PbTe family. An orientation relationship of (0001)Sb2Te3//{1 1 1}PbTe and < 1 1 (2) over bar0 > Sb2Te3//< 110 > PbTe was found with a maximum misorientation of 15 degrees. The Seebeck coefficient after annealing at 450 degrees C was -50 +/- 10 mu V degrees C-1 at room temperature. To improve the thermoelectric properties, tuning of the carrier concentration would be necessary. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.