Thermoelectric Properties of Minerals with the Mawsonite Structure

Synthetic copper sulfides have emerged as promising nontoxic and low-cost materials for thermoelectric power generation in low-grade waste heat recovery systems. Similarly to tetrahedrite and colusite, mawsonite Cu₆Fe₂SnS₈ exhibits a modified corner sharing Cu-S tetrahedral network which usually leads to p-type character and low thermal conductivity. In order to explore the applicative potential of mawsonite, we studied the band structure, the phonon dispersions, the electronic and transport coefficients, as well as the effect of isovalent substitutions of Fe, Sn, and S. The combined analysis of electronic and vibrational properties highlights the role of the weakly bonded copper component in achieving a very low thermal conductivity. We also demonstrate that the Cu-S bond builds a 2D conductive network where the contribution from other elements is negligible. Magnetic calculations point to an antiferromagnetic ground state substantially affected by the covalency of the bonds with the conductive plane. The chemical substitution of Fe with Ni leads to nonmagnetic metals whereas Cu₆Fe₂SnSe₈, Cu₆Fe₂PbS₈, and Cu₆Fe₂GeX₈ with X = S, Se, and Te are semiconductors.