Increase in the density of states in n-type extruded (Bi(1−x)Sbx)2(Te(1−y)Sey)3 thermoelectric alloys

Abstract

The concentration and doping of n-type doped (Bi(1−x)Sbx)2(Te(1−y)Sey)3 thermoelectric alloys produced by powder metallurgy followed by hot extrusion are varied in order to optimize their performance for the generation of electricity. The material is polycrystalline and strongly textured, with an undetermined volumetric fraction of nanoscale subgrains, and its thermoelectric properties are optimal along the extrusion direction. Within the composition range 0 ⩽ x, y ⩽ 0.1 the quaternary (Bi0.97Sb0.03)2(Te0.93Se0.07)3 shows the highest temperature-averaged dimensionless figure of merit ⟨ZT⟩ for applications where TC = 295 K and TH = 420 K. This average ⟨ZT⟩ is further optimized for values of carrier concentrations close to n = 3.4 × 1019 cm−3. The introduction of substitution elements constituting these quaternary alloys leads to an increase in the electronic equivalent density of states compared with Bi2Te3. This increase has a direct impact on the Seebeck coefficient, the electronic contribution to the thermal conductivity and the carrier mobility.