Excellent thermoelectric properties and stability realized in copper sulfides based composites via complex nanostructuring

Nanostructuring is a conventional approach to decrease thermal conductivity, nevertheless, the effect of grain boundaries on scattering phonon is limited. Herein, a new approach of constructing complex nanostructures is proposed. The copper sulfides-based nanocomposites with high thermoelectric properties and phase stability were fabricated by combining with solid-state reaction and spark plasma sintering techniques. The main phase of Cu₁₂Sb₄S₁₃ and Cu_1.96S with complex nanostructures is obtained by introducing CoSb₃ additive to Cu_1.8S matrix. Hole concentration in p-type composites is tailored by regulating Cu vacancies concentration and Co³⁺ doping in Cu⁺ sites, resulting in the significantly enhanced Seebeck coefficient and carrier thermal conductivity reduction. Furthermore, an ultralow thermal conductivity of 0.47 W m⁻¹ K⁻¹ at 773 K is achieved due to the tuned carrier concentration and the enhanced phonons scattering by continuous nanopores, extra phase interfaces and nanoprecipitates. The record high ZT of 1.6 is achieved at 773 K in Cu-S based thermoelectric material system for the composite specimen, namely Cu_1.8S-5 wt.% CoSb₃. Our result provides a new strategy to construct complex nanostructures and realize spontaneous composition regulation in improving TE performance of copper sulfide-based materials.