The Preparation of Very Small Grain Size Compacts of Lead Telluride

Abstract

Compacts of 2N-lead telluride with grain sizes of <5 μm and <0.5 μm have been prepared by hot pressure sintering at a temperature of approximately 1100 K and pressure of 10 MPa. The densities of the compacts were in excess of 8.0 gm cm-3 compared with the “single crystal” value of 8.25 gm cm-3. Compacts having densities closer to “singe crystal” values can be obtained but they exhibit cracks along planes perpendicular to the pressing direction. The room temperature thermal conductivity of 2N-lead telluride with a grain size <0.5 μm it is about 9% lower than equivalent “single crystal” material. After allowing for porosity effects the reduction in thermal conductivity is in excess of 8%. This experimental data lends support to the predicted reduction in lattice thermal conductivity with grain size. Within the experimental error, the Seebeck coefficient of annealed samples does nos change with reduction in grain size. However, both the Seebeck coefficient and electrical resistivity of “as compacted” material are significantly higher than single crystal material. It is concluded that the thermoelectric figure of merit of materials based upon lead telluride could be improved through the use of very small grain size material, provided the electrical properties can be retained close to single crystal values.