Solubility and formation of ternary Widmanstatten precipitates in PbTe in the pseudo-binary PbTe-Bi2Te3 system

A unidirectional solidification experiment by Bridgman method has been performed for the Pb14Bi28.8Te57.2 composition, which lies on the pseudo-binary PbTe-Bi2Te3 system, resulting in the formation of Widmanstatten precipitates of a ternary compound, most likely with the structure of PbBi2Te4 in the PbTe matrix. The formation of the precipitates is caused by the decrease of bismuth solubility in the PbTe phase with decreasing temperature. The PbTe-rich part of the PbTe-Bi2Te3 phase diagram was investigated from the compositional variations in the unidirectionally solidified sample and the diffusion couples. This proved that the solubility decreases with decreasing temperature: 15.6 +/- A 0.9 (583 A degrees C) to (450 A degrees C) at.% Bi. The orientation relationship between the matrix and precipitates has been examined by electron backscatter diffraction technique; precipitation occurs on {111} habit planes in PbTe with orientation relationship (0001)(precipitate)//{111}(PbTe) and The thermoelectric properties in PbTe with Widmanstatten precipitates as examined by the scanning Seebeck probe method is -46 +/- A 2 mu VK-1.