Cryogenic thermoelectric enhancements in SbCl3-doped porous Bi0.85Sb0.15 alloys

Abstract

In this work, porous Bi_0.85Sb_0.15/x vol% SbCl₃ (x = 0, 0.5, 1, 1.5, and 2) materials were prepared by melt-spinning combined with hot pressing and annealing, and the effects of SbCl₃ doping as well as the porous structure on their cryogenic thermoelectric performance were investigated. It is found that the nano/microscale porous structure is formed due to SbCl₃ sublimation during annealing, and meanwhile a small amount of SbCl₃ is doped into the Bi_0.85Sb_0.15 matrix simultaneously. The carrier concentration is reduced as a consequence of Cl doping, leading to a well-maintained PF (66 μW cm⁻¹ K⁻²) and a 27% reduction in κ_ele + κ_bip. A low κ_L of 0.71 W m⁻¹ K⁻¹ is obtained for the intense phonon scattering due to the porous structure. Thus, the maximum ZT value of 0.45 at 180 K is achieved for the Bi_0.85Sb_0.15/1 vol% SbCl₃ sample, and is increased by 45% compared with that of the Bi_0.85Sb_0.15 matrix. Under an external magnetic field, the enhancement of S compensates for the decrease in the electrical conductivity, resulting in an unchanged PF. With the suppression of κ_ele + κ_bip by the magnetic field and the reduction of κ_L by the porous structure, a low κ_tot of 1.56 W m⁻¹ K⁻¹ under 1 T is obtained. Finally, the maximum ZT value of 0.64 at 220 K under 1 T is achieved for the Bi_0.85Sb_0.15/1 vol% SbCl₃ sample, and is increased by 106% compared with that of the Bi_0.85Sb_0.15 matrix. This work demonstrates that SbCl₃ doping combined with a porous structure can synergistically regulate the electronic and thermal transport properties of the Bi_0.85Sb_0.15 alloy, and can further promote its cryogenic thermoelectric performance.