Improving thermoelectric performance of (Bi0.2Sb0.8)2(Te0.97Se0.03)3 via Sm-doping

Abstract

We herein report the effects of Sm doping on the thermoelectric performance of (Bi0.2Sb0.8)2(Te0.97Se0.03)3 compounds prepared by a growth-from-the-melt spark-plasma-sintering procedure. In conjunction with micro-morphology and compositional analyses, the electrical conductivity, Seebeck coefficient, and thermal conductivity of (Bi0.2-xSmxSb0.8)2(Te0.97Se0.03)3 samples were measured as a function of temperature (298–473 K) and the Sm doping ratio (x = 0%, 0.2%, 0.4%, and 0.8%). We found that (i) there was no discernible crystal lattice symmetry change upon Sm doping; (ii) Sm doping generally increased the electric conductivity and practically retained the Seebeck coefficient, thereby yielding higher power factors; and (iii) specially, a minimum thermal conductivity ∼ 0.92 Wm−1K−1 was attained in the x = 0.4% sample at 423 K, resulting in a state-of-the-art ZT value ∼ 1.22, which is ∼25% higher than the maximum ZT value of pristine sample. Contrary to the customary view that Sm dopant adopts a trivalent state Sm3+, the variations of lattice constant pointed toward a lower valence state of Sm. The results demonstrated the efficacy and deepened our understanding of rare earth doping in thermoelectric study of Bi2Te3-based materials.