Twin engineering in solution-synthesized nonstoichiometric Cu₅FeS₄ icosahedral nanoparticles for enhanced thermoelectric performance

Abstract

A facile colloidal solution method has been developed for the fast, scalable synthesis of orthorhombic@cubic core–shell nonstoichiometric Cu₅FeS₄ icosahedral nanoparticles. Such nanoparticles contain high-density twin boundaries in the form of fivefold twins. Spark plasma sintering consolidates the nanoparticles into nanostructured pellets, which retain high-density twin boundaries and a tuned fraction of the secondary phase Fe-deficient cubic Cu₅FeS₄. As a result, the thermal and electrical transport properties are synergistically optimized, leading to an enhanced zT of ≈0.62 at 710 K, which is about 51% higher than that of single-phase Cu₅FeS₄. This study provides an energy-efficient approach to realize twin engineering in nonstoichiometric Cu₅FeS₄ nanomaterials for high-performance thermoelectrics.