Enhanced Thermoelectric Performance of Lightly Pb-Doped Sb2Te3 Polycrystalline Alloys for Power Generation in Midtemperature Range

Abstract

Sb2Te3 alloys are promising thermoelectric materials because of their outstanding electrical transport properties in the midtemperature range of 500–700 K, while codoping with multiple elements has been successful to improve their thermoelectric performance. In this study, enhanced thermoelectric properties with a maximum thermoelectric figure of merit of 0.97 are reported for singly and lightly Pb-doped Sb2Te3 polycrystalline alloys (Sb2– ${}_x$ Pb ${}_x$ Te3). Very light Pb doping in the range $0.005\le x\le 0.0125$ in the Sb2– ${}_x$ Pb ${}_x$ Te3 alloys yielded significantly improved carrier transport properties and increased electrical conductivity while the Seebeck coefficient is decreased moderately, since the density-of-state effective mass is improved much. As a result, power factor for the Pb-doped Sb2Te3 is largely increased up to 3.7 mW/mK2 at 300 K. The lattice thermal conductivity decreased considerably owing to the additional point defect phonon scattering by the Pb despite slight doping. Consequently, a maximum thermoelectric figure of merit of 0.97 was obtained for Sb1.9875Pb0.0125Te3 ( $x=0.0125$ ) at 600 K, which is the highest reported value for singly doped Sb2Te3-based alloys. A maximum energy conversion efficiency was calculated to be 9.0% for a temperature difference of 350 K, which is higher than that for other singly or codoped Sb2Te3 alloys.