Thermoelectric and Mechanical Properties of Pb-Doped Sb2Te3–Bi2Te3 Solid Solutions

We have studied the properties of samples prepared by hot-pressing and extruding granules produced by solidifying molten Pb-doped Sb2Te3–Bi2Te3 solid solutions (24 and 25 mol % Bi2Te3, 0.04 to 0.14 wt % Pb) in a liquid and comminuted in a mortar, cutting mill, or planetary mill. Their microstructure and fractographs have been investigated using an optical and a scanning electron microscope. The results demonstrate that doping with Pb has no significant effect on the compressive strength of the materials, which depends on the sample preparation procedure and is lowest in the case of the samples prepared by hot-pressing granules comminuted in the cutting mill. The highest strength is offered by the samples prepared by extrusion of 25-mm-diameter rods. Doping with Pb increases carrier concentration (reduces the Seebeck coefficient) and shifts the peak in the thermoelectric figure of merit of the materials, (ZT)max, to higher temperatures. The highest thermoelectric figure of merit, (ZT)max = 1.1 ± 0.1, has been obtained at 360 K for the Bi0.5Sb1.5Te3 solid solution doped with 0.05 wt % Pb and prepared by extruding granules comminuted in the planetary mill.