Influence of processing parameters on the thermoelectric properties of (Bi0.2Sb0.8)2Te3 sintered by ECAE

Equal Channel Angular Extrusion (ECAE) has been recognized as one of the most successful process for nanopowder consolidation. By operating at lower temperatures than needed for Hot Pressing, it allows a better control of the competition between powder consolidation and coarsening. In this work, we report preliminary results on the influence of ECAE parameters on the thermoelectric properties of p-type (Bi0.2Sb0.8)2Te3 nanopowders. The latter, prepared by ball milling elemental chunks, were compacted at room temperature under Ar atmosphere, and encapsulated into a Cu can for ECAE processing. The so called route C was used, with a punch speed of 5 mm min-1. Two ECAE passes at 300 °C were sufficient to consolidate the material; however, the electrical conductivity was depressed, because of the introduction of n-type defects at this temperature. A satisfactory compromise among ?, ?, and ?, was achieved by operating at 385 °C, both with two and four ECAE passes. A value of ZT close to 1, from room temperature to 95 °C, was reached. Enhancement of the figure of merit is expected by further increasing the number of ECAE passes at this temperature (material texturing improvement), provided the total processing time is substantially shortened, in order to preserve the nanograined structure.