Morphology and phase evolution from CuS to Cu1.8S in a hydrothermal process and thermoelectric properties of Cu1.8S bulk

Abstract

CuS microflowers self-assembled from nanosheets were prepared by hydrothermal synthesis (HS) using CuCl₂·2H₂O and CS(NH₂)₂ as raw materials and glycol as a solvent at 120 and 140 °C for 1.5 h. With increasing the hydrothermal temperature or reaction time, the CuS microflowers break up to Cu_1.8S nanoparticles. The single phase Cu_1.8S nanoparticles were obtained at 200 °C for 10 h. The evolution route of the phase structure and microstructure from CuS to Cu_1.8S was investigated. The Cu_1.8S particles were densified to bulk materials by applying spark plasma sintering (SPS) technology. The fine-grain bulk Cu_1.8S had a Seebeck coefficient of 73 μV K⁻¹ and a thermal conductivity of 1.15 W m⁻¹ K⁻¹ at 673 K, resulting in an enhanced ZT value of 0.49 at 673 K, which is the highest value for pristine Cu_1.8S in the literature. Our work indicates that the Cu_1.8S system is a potential candidate with low costs and toxicity in mid-temperature thermoelectric application.