Sulfur simultaneously act as pore-forming agent and doping agent to improve the thermoelectric properties of Bi2Te2.7Se0.3

Abstract

Constructing nanopores in the solid is considered as an effective mean for suppressing thermal conduction, nanoporous materials have shown a desired potential for thermoelectric application. Herein, a simple two-step method is employed to construct nanopores in commercial n-type Bi2Te2.7Se0.3 (BTSe) material by evenly mixing sulfur with Bi2Te2.7Se0.3 powders and then hot-pressing. Some of sulfur can be sublimed to leave pores with the size of 50–300 nm on the surface of BTSe grains and others can be doped into the lattice of BTSe to achieve substitution of isoelectric atoms. In other words, sulfur can simultaneously act as pore-forming agent and doping agent to form defects with different scales in BTSe, contributing collectively to enhanced phonons scattering. The results show that the effective mass md∗ is enhanced and thus Seebeck coefficient α is increased after introducing nanopores and point defects (sulfur substitution). And high carrier mobility μ is still maintained due to increased grain size even though nanopores and sulfur substitution are unfavorable it. Consequently, a peak ZT of 0.85 at 473 K and average ZT of 0.74 at 300–548 K are achieved in this work, both of which increase by about 50% compared to those of initial BTSe.