Powder metallurgical processing of functionally graded p-Pb_1-xSn_xTe materials for thermoelectric applications

Lead tin telluride-based compounds are p-type materials for thermoelectric applications, in the 50-600 °C temperature range. The electronic transport properties of PbTe and Pb_1-xSn_xTe materials are strongly dependent on the processing approach. Powder metallurgy is a suitable approach for the preparation of Functionally graded materials (FGMs) but its effects on the electronic properties have to be carefully checked. Powder metallurgical processing may introduce atomic defects and local strains into the material and, thereby, alter the carrier concentration. Such material may be in non-equilibrium conditions at the operating temperature with unstable thermoelectric properties. This effect can be reduced and eliminated by appropriate annealing procedures. In FGMs, annealing up to the stabilization of the thermoelectric properties is mandatory for achieving the desired carrier concentration profile along the sample. The design procedures of the FGMs, as well as the annealing effects on cold compacted and sintered Pb_1-xSn_xTe samples are described in details.