Electronic Transport and Thermoelectric Properties of Cu12-xZnxSb4S13 Tetrahedrites Prepared by Mechanical Alloying and Hot Pressing

Tetrahedrite Cu12Sb4S13 has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. When the Cu atoms of Cu12Sb4S13 are partially substituted with a transition metal, changes in the Cu vibrations can intensify phonon scattering, thereby enhancing the thermoelectric properties. The synthesis of tetrahedrite compounds by conventional melting methods requires sophisticated reactions because the S element vaporizes at low temperature and its homogenization requires a long time. However, a homogeneous and solid-state synthesis can be carried out in a short time using mechanical alloying, because the volatilization of the constituent elements is inhibited and the subsequent heat treatment is not necessary. In this study, Zn-doped Cu12-xZnxSb4S13 tetrahedrites were prepared by mechanical alloying (MA) and hot pressing (HP), and their electronic transport and thermoelectric properties were examined. A single tetrahedrite phase was successfully obtained by the MA-HP process without subsequent heat treatment. The lattice constant increased with the Zn content, confirming that Zn was substituted for Cu. Zn doping led to p-type conduction characteristics; however, it did not effectively increase the power factor. However, the thermal conductivity showed a marked decrease upon Zn doping, due to decrease in carrier contribution. A dimensionless figure of merit of 0.76 was obtained at 723 K for Cu11.6Zn0.4Sb4S13.