Andrzej Kolezynski | Searcharxiv

arXiv2024

First-principles calculations of structural and bonding properties of Li-doped tetrahedrite thermoelectrics

Tetrahedrite (copper antimony sulfosalt) is promising p-type themoeletric material due to very low intrinsic thermal conductivity and moderately-high power factor, with one of the limitations being lack of n-type variant to create thermoelectric generator. In this paper, DFT calculations have been carried out to study tetrahedrite doped with Li into structural voids, LixCu12Sb4S13 (0 <= x <= 3). Enthalpies of formation shows that introduction of Li into both 6b and 24g sites is energetically favorable. Dopants in those positions differently affect rattling Cu(12e) behaviour, as well as vary in magnitude of induced local disorder. Topological analysis of charge density classifies tetrahedrite as closed-shell, ionic system of interactions with some degree of covalency. Addition of Li increases bond strain and decreases structure stability. Electronic band structure shows that for x>2.0, material becomes n-type, however results are not precisely conclusive on whether structure will be synthesizable, which should be determined experimentally.

cond-mat.mtrl-sci↗

arXiv2022

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

cond-mat.mtrl-sci↗