First-principles study of structural disorder, site preference, chemical bonding and transport properties of Mg-doped tetrahedrite

Tetrahedrite-based ($\textrm{Cu}_{12}\textrm{Sb}_{4}\textrm{S}_{13}$) materials are candidates for good thermoelectric generators due to their intrinsic, very low thermal conductivity and high power factor. One of the current limitations is virtual absence tetrahedrites exhibiting n--type conductivity. In this work, first-principles calculations carried out study Mg-doped tetrahedrite, $\textrm{Mg}_{x}\textrm{Cu}_{12}\textrm{Sb}_{4}\textrm{S}_{13}$ with possibility predicting material in mind. Different concentrations modifications structure investigated formation energies, preferred site occupation change local environment around dopants. Mg atoms tend occupy 6b site, while introduced excess Cu prefers 24g site. Introduction elements those sites display different effect on nearby rattling Cu(2) atom. Topological analysis shows that tetrahedrite exhibits ionic, closed-shell bonds some degree covalency. Majority weakens increasing content Mg; becomes increasingly less stable, which also expressed by global instability bond strain indexes. Achieving was predicted structures $x>1.0$, however enthalpy lack stability might suggest limit solubility difficulties obtaining experimentally.