Realizing Enhanced Thermoelectric Performance and Hardness in Icosahedral Cu 5 FeS 4- x Se x with High-Density Twin Boundaries

Bornite (Cu FeS ) is an Earth-abundant, nontoxic thermoelectric material. Herein, twin engineering and Se alloying are combined in order to further improve its thermoelectric performance. Cu FeS Se (0 ≤ x ≤ 0.4) icosahedral nanoparticles, containing high-density twin boundaries, have been synthesized by a colloidal method. Spark plasma sintering retains twin boundaries in the pellets sintered from Cu FeS Se colloidal powders. Thermoelectric property measurement demonstrates that alloying Se increases the carrier concentration, leading to much-improved power factor in Se-substituted Cu FeS , for example, 0.84 mW m K at 726 K for Cu FeS Se ; low lattice thermal conductivity is also achieved, due to intrinsic structural complexity, distorted crystal structure, and existing twin boundaries and point defects. As a result, a maximum zT of 0.75 is attained for Cu FeS Se at 726 K, which is about 23% higher than that of Cu FeS and compares favorably to that of reported Cu FeS -based materials. In addition, the Cu FeS Se samples containing twin boundaries also obtain improved hardness compared to the ones fabricated by melting-annealing or ball milling. This work demonstrates an effective twin engineering-composition tuning strategy toward enhanced thermoelectric and mechanical properties of Cu FeS -based materials.