Formation of Sb2Te3 Widmanstätten 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 Widmanstätten precipitates of Sb2Te3. The precipitation is due to a decrease in the solubility of Sb2Te3 with temperature: the solubility at 450 °C was determined to be 2.1 ± 0.2 at.% Sb. The average thickness of plates was estimated to be ∼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 (0 0 0 1)Sb2Te3//{1 1 1}PbTe and <1 1 2¯ 0>Sb2Te3//<1 1 0>PbTe was found with a maximum misorientation of 15°. The Seebeck coefficient after annealing at 450 °C was −50 ± 10 μV °C−1 at room temperature. To improve the thermoelectric properties, tuning of the carrier concentration would be necessary.