Abstract
Large-scale Cu2S tetradecahedrons microcrystals and sheet-like Cu2S nanocrystals were synthesized by employing a hydrothermal synthesis (HS) method and wet chemistry method (WCM), respectively. The morphology of α-Cu2S powders prepared by the HS method is a tetradecahedron with the size of 1–7 μm. The morphology of β-Cu2S is a hexagonal sheet-like structure with a thickness of 5–20 nm. The results indicate that the morphologies and phase structures of Cu2S are highly dependent on the reaction temperature and time, even though the precursors are the exact same. The polycrystalline copper sulfides bulk materials were obtained by densifying the as-prepared powders using the spark plasma sintering (SPS) technique. The electrical and thermal transport properties of all bulk samples were measured from 323 K to 773 K. The pure Cu2S bulk samples sintered by using the powders prepared via HS reached the highest thermoelectric figure of merit (ZT) value of 0.38 at 573 K. The main phase of the bulk sample sintered by using the powder prepared via WCM changed from β-Cu2S to Cu1.8S after sintering due to the instability of β-Cu2S during the sintering process. The Cu1.8S bulk sample with a Cu1.96S impurity achieved the highest ZT value of 0.62 at 773 K.
Highlights
Thermoelectric (TE) material is a kind of energy conversion material which takes advantage of solid material internal carriers and phonon interactions to convert thermal and electrical energy directly into each other
All of the diffraction peaks of the hydrothermal synthesis (HS) sample are well-matched with the standard card of α-Cu2 S
All of the diffraction peaks of the wet chemistry method (WCM) sample are well-matched with the standard card β-Cu2 S
Summary
Thermoelectric (TE) material is a kind of energy conversion material which takes advantage of solid material internal carriers and phonon interactions to convert thermal and electrical energy directly into each other. Compared to the mainstream tellurium-based TE materials [5,6,7,8], nanostructured metal chalcogenides with low cost, low toxicity, and abundant elements exhibit interesting physical properties [9,10]. Cu2 S is of high interest due to its unique electronic, thermodynamic, optical, and other physical and chemical properties. It has great potential in a wide range of applications such as thermoelectric materials [19], solar cells [20,21], conductive fibers [22], optical filters [23], and high-capacity cathode materials in lithium secondary batteries [24]. The thermoelectric properties of all the bulk samples were measured
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