First-Principles Studies of Earth-Abundant Tetrahedrite Thermoelectrics

Recent experiments have shown inexpensive and naturally occuring tetrahedrite-based materials that exhibit a thermoelectric figure of merit near unity. These compounds are typically of the form Cu$_{12-x}$M$_{x}$Sb$_{4}$S$_{13}$, where M is a transition metal, such as Zn or Fe, for a wide range of x. Using density-functional theory calculations, the ternary phase diagram and various defect formation energies are calculated. Furthermore, the electronic structure, phonon spectrum and thermoelectric properties are investigated. We observe metallic behavior and strong lattice anharmonicity of stoichiometric Cu$_{12}$Sb$_{4}$S$_{13}$. In addition, doping with transitional metals Zn or Fe increases both resistivity and anharmonicity. The theoretical calculations are in good agreement with experimental measurements.