Thermoelectric Properties of Lead Tin Telluride Compacts

Abstract

In this paper the effects of grain size on the thermoelectric properties of compacts of PbSnTe are investigated. The preparation of compacts with a grain size L in the range 25<L<60, 10<L<25, 5<L<10 and <5 m is described and the results of measurements of the thermal conductivity, Seebeck coefficient and electrical resistivity reported. At room temperature the thermal conductivity of compacts with a grain size <5 pm is about 70% that of material with a grain size 25<L<60 p m and this reduction increases further with an increase in temperature. As pressed compacts possess degraded electrical properties compared to “single crystal” material and heat treatment procedures are employed to improve the electrical properties.

It is concluded that the thermal conductivity of PbSnTe alloys can be reduced by the use of very small grain size compacted material. The behaviour of the electrical properties both as a function of grain size and temperature is problematic and attests the complicated relationship between the physical and transport properties of compacted materials. All three parameters which occur in the thermoelectric figure of merit are sensitive to high temperature heat treatment and in judiciously heat treated material the reduction in the thermal conductivity of the smallest grain size material compared to that of the largest grain size more than compensated for the degradation in electrical properties. This resulted in an improvement in the thermoelectric figure of merit of the specimen investigated.