Microstructure and Thermoelectric Properties of n-type Chalcogenide Nanopowders Sintered by ECAE

Nanograined powders of Bi1.9Sb0.1Te2.85Se0.15 alloy have been consolidated into bulk ingots by warm ECAE process. Sintering has been achieved after only two ECAE passes at 300 °C, with a total holding time at this temperature of 19 minutes. The morphological characterization of ECAE processed samples, performed by HRTEM, has shown grain sizes varying from 20 to 50 nm. Thermoelectric properties, measured at 300 K show that the thermal conductivity is considerably reduced by the nanostructure, but the value of the Seebeck coefficient is relatively low, due to a non optimized value of the electron concentration. The latter result has been attributed to oxygen contamination.