Formation of Sb_2Te_3 Widmanstätten precipitates in thermoelectric PbTe

Abstract

Unidirectional solidification experiments have been performed with a thermoelectric alloy with a starting composition of Pb_(10.5)Sb_(31.6)Te_(57.9) in the pseudobinary PbTe–Sb_2Te_3 system. The bottom of the resulting rod consists of PbTe phase with Widmanstätten precipitates of Sb_2Te_3. The precipitation is due to a decrease in the solubility of Sb_2Te_3 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 {111}PbTe family. An orientation relationship of (0001)Sb_2Te_3//{111}PbTe and <1120>Sb_2Te_3//<110>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.

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