Synergistic effect of grain boundaries and phonon engineering in Sb substituted Bi2Se3 nanostructures for thermoelectric applications.

Phonon scattering by intrinsic defects and nanostructures has been the primary strategy for minimizing the thermal conductivity in thermoelectric materials. In this work, we present the effect of Isovalent substitution as a method to decouple the Seebeck coefficient and the thermal conductivity of antimony (Sb) substituted bismuth selenide (Bi2Se3). Transmission electron microscopy studies present the nanostructured Bi2-xSbxSe3 thermoelectric system represents the coexistence of hierarchical defect structure and dislocations. The observed giant reduction in thermal conductivity is due to the multi-scale phonon scattering caused by a combination of stacking faults, lattice dislocations and grain boundary scattering. This study reveals that a large number of dislocations about ∼1.09 × 1016 m-2 are particularly effective at lowering thermal conductivity. We achieved one of the ultra-low thermal conductivity values (∼0.26 W/m K) for the maximized dislocation concentration. Moreover, Isovalent substitution provides a new avenue for the reduction in thermal conductivity and significant enhancement in the Seebeck coefficient of thermoelectric materials.