A Flash Vacuum‐Induced Reaction in Preparing High Performance Thermoelectric Cu2S

Abstract Synthesis of high‐performance thermoelectric (TE) materials with tunable compositions and nanostructures normally require sophisticated and high‐cost methods, such as high‐temperature melting and solid‐state reactions, which consume a large amount of time and energy and incur high costs. Herein, a fast, reliable, low‐cost, and environmentally friendly method, namely the vacuum‐induced method, is developed to rapidly synthesize Cu 2 S‐based materials with high TE performance. By mixing finely ground powders of metal‐Cu and S at room temperature, Cu 2–x S compounds with a tunable x varied from 0–0.07 can be instantly formed by a quick sulfurization reaction once the mixture is placed inside a low vacuum (≈about 30 Pa and beyond). The atomic mechanism of Cu 2–x S formation is studied by transmission electron microscopy, as a heterogeneous growth with the diffusion of both Cu + ‐cations and S 2− ‐anions. In a low vacuum, the sulfur vapor is preferably attached to the copper surface with rich defected sites such as atomic vacancies, steps, and edges. The synthesized Cu 2–x S powders with further plasma‐activated sintering treatment show high TE performance with ZT ≈ 1.56 around 800 K. Such a simple synthesis method may provide an effective and low‐cost way to prepare sulfides with potential applications in TE materials and solid electrolytes.