Achievement of Excellent Thermoelectric Properties in Cu–Se–S Compounds via In Situ Phase Separation

In this study, Cu2Se1–xSx (x = 0.1, 0.3, and 0.5) alloy powders were prepared by the hydrothermal synthesis method. In the subsequent sintering process, the spontaneous in situ phase separation process of the sample forms a two-phase hybrid structure. The generated Cu2S precipitates in the Cu2Se matrix noticeably enhance phonon scattering, which is beneficial for low thermal conductivity without significantly affecting the electrical transport performance. Ultimately, an optimized thermoelectric performance was obtained in Cu2Se0.9S0.1, reaching a peak zT value of 1.43 at 773 K, the optimum value among the Cu–Se–S systems at this temperature.