Critical evaluation of p-type doping effects in Bi-Sb alloys

Xixiao Hu,S Joseph Poon,Sheng Gao

doi:10.1063/1.5108956

Abstract

We have investigated the doping effects of elements (Sn, Pb, Ge) with valence 4 in Bi-Sb alloys. The solubilities of these elements in Bi-Sb alloy are known to range from ∼3 to ∼0.5 to zero atomic percent, respectively. We employed a rapid solidification method to prepare samples that allowed us to achieve a high doping level of Ge and a high doping efficiency of Pb in Bi85Sb15. Using this method, unprecedented high Ge content (up to 13 atomic percent) could be solutionized in Bi-Sb. Microstructure analyses and thermoelectric transport property measurements have been performed on the doped samples which all showed p-type properties at cryogenic temperatures. The doping efficiency of the elements (Sn, Pb, Ge) was calculated based on the Hall measurements and discussed in light of donor and acceptor sites in Bi-Sb. A two-band effective mass model was used to simulate the thermoelectric transport properties within the Boltzmann transport theory. The present study revealed a gap-decreasing phenomenon in the undoped and doped samples. This gap-decreasing behavior is a heretofore unrealized obstacle to achieving a high thermoelectric figure of merit in p-type Bi-Sb alloys.

Highlights

Relative to conventional power generators or refrigerators, thermoelectric (TE) technology provides a more stable, quiet, and environmentally-friendly method for heat-electrical energy conversion, and receives much research attention.1 the limitation of the energy conversion efficiency of TE devices makes them less competitive in many situations
X-ray diffraction (XRD, PANalyticalX’Pert pro MPD instrument) was employed to check if there was any second phase in the samples
The ribbons were pulverized with a mortar and pestle and the alloy powders were compacted into a solid disk using spark plasma sintering (SPS)

Summary

Introduction

Relative to conventional power generators or refrigerators, thermoelectric (TE) technology provides a more stable, quiet, and environmentally-friendly method for heat-electrical energy conversion, and receives much research attention.1 the limitation of the energy conversion efficiency of TE devices makes them less competitive in many situations. Researchers have done much work on Ge/Sn/Pb doped Bi-Sb,8–10,18,19 but high levels of doping have not been reported due to the low or even zero solubility of those elements in Bi or Sb. Using melt-spinning (MS) and low-temperature spark plasma sintering (low-T SPS), we have successfully introduced a high concentration of dopants into Bi-Sb with higher doping efficiency. The numerical simulation based on two-band effective mass model has not been performed on the TE transport properties of p-type doped Bi-Sb alloys.

Results

Conclusion