Enhanced thermoelectric properties of Cu1.8S via the introduction of ZnS nanostructures†

Copper sulfide (Cu_1.8S) has attained widespread recognition over the past few years because of its superior electrical conductivity, thermal stability and low-cost raw materials. In this work, we studied the influence of nanostructured ZnS on the thermoelectric properties of Cu_1.8S. The nanocomposites of Cu_1.8S + x wt% ZnS (x = 0, 5, 10 and 20) were treated hydrothermally and sintered using cold pressing technique. XRD patterns validated the material structure, purity of the phase and the presence of the ZnS phase, whereas backscattered electron micrographs with EDX elemental mapping displayed secondary CuS phase precipitation on the Cu_1.8S matrix, supporting SEM patterns. Eventually, a considerable improvement in the Seebeck coefficient to 63.44 μV K⁻¹ at 573 K was achieved as a result of ZnS incorporation-driven low energy carrier filtering, thereby leading to a power factor of 525.12 μW mK⁻² at 573 K for the Cu_1.8S + 5 wt% ZnS sample. Scattering from CuS mesoscale structures, pores and point defects collectively suppressed lattice thermal conductivity and thereby reduced the total thermal conductivity to 2.64 W mK⁻¹ at 323 K for Cu_1.8S + 5 wt% ZnS by significantly enhancing the zT to 0.08 at 573 K.