Effects of Doping on Transport Properties in Cu–Bi–Se-Based Thermoelectric Materials

The
thermoelectric properties of Zn-, In-, and I-doped Cu1.7Bi4.7Se8 pavonite homologues were investigated
in the temperature range from 300 to 560 K. On the basis of the comprehensive
structural analysis using Rietveld refinement of synchrotron radiation
diffraction for Cux+yBi5–ySe8 compounds with the inherently disordered
crystallographic sites, we demonstrate a doping strategy that provides
a simultaneous control for enhanced electronic transport properties
by the optimization of carrier concentration and exceptionally low
lattice thermal conductivity by the formation of point defects. Substituted
Zn or In ions on Cu site was found to be an effective phonon scattering
center as well as an electron donor, while doping on Bi site showed
a moderate effect for phonon scattering. In addition, we achieved
largely enhanced power factor in small amount of In doping on Cu site
by increased electrical conductivity and moderately decreased Seebeck
coefficient. Coupled with a low lattice thermal conductivity originated
from intensified point defect phonon scattering by substituted In
ions with host Cu ions, a thermoelectric figure of merit ZT of 0.24 at 560 K for Cu1.6915In0.0085Bi4.7Se8 was achieved, yielding 30% enhancement compared
with that of a pristine Cu1.7Bi4.7Se8 at the same temperature.