Nanoengineering Approaches to Tune Thermal and Electrical Conductivity of a BiSbTe Thermoelectric Alloy

Nanoengineering of thermoelectric (TE) materials is an effective approach to decouple their electronic and thermal transport properties, hence enhancing their TE efficiency. Nanoengineering strategies can significantly reduce the thermal conductivity through the corporation of different phonon scattering mechanisms, whereas the electrical conductivity may not be affected considerably. Herein, the effects of three nanoengineering approaches on the structural, electrical, and thermal properties of Bi0.5Sb1.5Te3 (BST) alloy are compared: (a) nanohybridization of the alloy by adding Sb2O3 nanoparticles, (b) severe plastic deformation via high-pressure torsion, and (c) grain refinement by sonication of BST powders before sintering. It is shown that among these methods, severe plastic deformation induces ultrafine grains and a high density of dislocations, resulting in a large reduction of the total thermal conductivity (32.8%) and a moderate decline in the electrical conductivity of (15.7%) at 300 K. A notable decrease in the lattice thermal conductivity (56.8% at 300 K) is attributed to midfrequency phonon scattering by the dislocations together with low and high frequency scatterings through grain boundaries and point defects, respectively. A new pathway is opened for designing highly efficient TE materials through nanoengineering approaches, particularly severe plastic deformation.