Structural and thermoelectric properties of iodine doped Cu-based argyrodites

Rietveld refinement and theoretical calculations confirm that iodine preferentially occupies the Q3 (4a) anion site. In the charge non-balanced samples, doping inefficiencies result in the presence of both electron and hole carriers, leading to complex transport behavior. Conversely, in the charge-balanced samples, iodine substitution increases the hole concentration by creating Cu⁺ vacancies, which also modifies the Seebeck coefficient and enhances the power factor at elevated temperatures.

As a result, iodine-doped Cu7.9SiS2.95Se2.95I0.1 achieves a high thermoelectric figure of merit (ZT ≈ 0.9 at 773 K), demonstrating strong potential for mid-temperature thermoelectric power generation.