Magnetic iron doping in Cu₂SnS₃ ceramics for enhanced thermoelectric transport properties

Thermoelectric properties of Fe-doped Cu₂SnS₃ (Cu₂Sn_1-xFe_xS₃, x = 0-0.25) ceramics were studied in relation to magnetoelectric interaction. Phase composition changed from monoclinic-dominating to cubic-and-tetragonal-dominating with increasing x. Electrical conductivity improved effectively with a metallic behavior below 520 K, while it increased unusually at higher temperatures with x over 0.15, caused by an increased carrier concentration as a result of the ferro-to-paramagnetism transition in heavily doped samples. Benefiting from the Fe-induced spin entropy and the enhanced density of states due to the participation of Fe-3d orbitals, the Seebeck coefficient is much higher than that for non-magnetism doping, leading to a large power factor of 1.15 mW m^-1 K^-2. With a low lattice thermal conductivity owing to cation-disordering and soft bonding, a maximal ZT of ∼0.75 has been achieved at 723 K in the x = 0.15 sample, which stands one among the top of Cu-based ternary chalcogenides.