Ultralow Lattice Thermal Conductivity and High Thermoelectric Figure of Merit in Dually Substituted Cu12Sb4S13 Tetrahedrites

The thermoelectric properties of dually substituted Cu12-xInxSb4S12.8Se0.2 tetrahedrites are studied in temperature range from 300 to 723 K. The results indicate that dual substitution of In for Cu and Se for S not only causes the enhancement of thermopower S but also gives rise to a significant decrease in lattice thermal conductivity kappa(L). An ultralow kappa(L) approximate to 0.2 W m(-1) K-1 is obtained at 723 K in Cu11.95In0.05Sb4S12.8Se0.2 sample due to the enhanced phonon scattering mainly by point defects. Consequently, a high figure of merit ZT(max) approximate to 1.0 is achieved in Cu11.95In0.05Sb4S12.8Se0.2 sample, which is approximate to 56% larger than that of pristine Cu12Sb4S13, indicating that dual substitution is effective in boosting the thermoelectric properties of tetrahedrites.