Enargite (Cu3AsS4): a ductile mid-temperature thermoelectric material†

Despite their intrinsic large band gap, low carrier concentration, and electrical conductivity, sulfide-based thermoelectric materials have been explored extensively because of their abundance and feasibility. This report uncovers the thermoelectric performance of Cu₃AsS₄ by combining density functional theory, the modified Debye–Callaway model, and phonon Boltzmann transport equations. The overall assessment of thermal, mechanical, and dynamical stability is confirmed through the ab initio molecular dynamics simulations, elastic constants, and phonon dispersion computations. The ultra-low lattice thermal conductivity of 0.327 and 1.020 W m⁻¹ K⁻¹ at 900 K obtained through various approaches can be attributed to the scattering of phonons induced by bonding heterogeneity and large lattice anharmonicity. Also, to improve the reliability of electronic transport properties, the carrier relaxation time is calculated by including acoustic, optical, and impurity phonon scattering mechanisms. The favourable band features and electron and phonon characteristics collectively facilitate a larger optimum power factor accompanied by the figure-of-merit of 1.07 to 2.31 at 900 K for p-type Cu₃AsS₄. These results highlight the potential applicability of Cu₃AsS₄ for mid-temperature thermoelectric applications. Also, this work elaborates the relationship between physical and mechanical characteristics of the crystal structure, which intensifies the understanding from materials to devices.