Synergistic modulation of mobility and thermal conductivity in (Bi,Sb)2Te3 towards high thermoelectric performance

Abstract

Modulating microstructures in a wide range from atomic defects to microscale structures independently can partially decouple the transport of charge carriers and phonons and thus enhance the figure of merit (zT) of thermoelectric materials. High mobility requires atomic scale purity, while introducing nanoscopic inhomogeneities leads to low thermal conductivity. Through a two-step sintering process with excess Te, lower reduction of mobility and decreased thermal conductivity were simultaneously achieved in (Bi,Sb)₂Te₃. Grain boundaries and defects that strongly impede charge carrier transport are reduced by the two-step sintering process leading to a higher mobility compared to that of the one-step sintered bulk. At the same time, removal of Te as well as Sb-rich inhomogeneities with lattice misfit to the matrix decreased the thermal conductivity. In this way, simultaneous maintenance of high mobility and low lattice thermal conductivity was illustrated. By further optimization of carrier concentration, the produced material showed an encouraging zT value of 1.38 at 323 K. The present work demonstrates a method for synthesizing high-efficiency thermoelectric materials through simultaneous optimization of the electrical and thermal transport properties.