Compositional and structural evolution advance thermoelectric performance of copper sulfides

The thermoelectric (TE) performance of copper sulfides relies on the phase structure, which is sensitive to the synthesis conditions and composition. To date, precisely adjusting the phase structure of copper sulfides is still a challenge. Herein, a novel path to regulate the phase structure and composition while introducing multiscale precipitates is proposed. This approach is effective in optimizing the electrical and thermal transport properties of copper sulfide-based composites. BFe was introduced into the Cu_1.8S material, and B atoms occupied the interstitial sites of the matrix, decreasing the solid solubility of Fe in copper sulfide. Then, the electron probe microanalysis (EPMA) and transmission electronic microscopy (TEM) Fe atoms partially consumed Cu and S to form multiscale Cu₅FeS₄ precipitates. The carrier concentration of the bulk composites was tuned by compositional variation, resulting in an improved Seebeck coefficient. The existence of multiscale precipitates, phase interfaces, dislocations and point defects scatter all-scale phonons, and the thermal conductivity of the samples was maintained at about 0.35 W m⁻¹ K⁻¹ throughout the entire temperature range. Ultimately, a peak ZT value of 1.13 was realized at 773 K for the Cu_1.8S + 1.25 wt% BFe sample, which was a 130 % increase over that of the pure sample of ∼0.49. This study proposes a route to realize compositional and structural evolution for enhancing thermoelectric performance, which might be useful in other systems.