Enhanced thermoelectric and mechanical properties of Cu1.8S1−xPx bulks mediated by mixed phase engineering†

Abstract

Copper sulfide is considered an advanced thermoelectric material due to its non-toxic nature and cost-effectiveness. Nevertheless, as a superionic conductor, Cu_1.8S demonstrates exceptionally high conductivity, and its thermoelectric properties can be improved by adjusting the carrier concentration. In this study, samples of Cu_1.8S_1−xP_x (x = 0–0.04, with an interval of 0.01) were designed using a combination of melting and spark plasma sintering techniques. The phase composition of the matrix changed from Cu_1.8S to Cu_1.96S and Cu₂S through the artificial reduction of S content, resulting in increased grain size and lower concentrations of multidimensional defects. Compared to the pure sample, the carrier mobility of the Cu_1.8S_0.97P_0.03 sample ultimately increased from 32 to 71 cm² V⁻¹ s⁻¹, attaining a maximum ZT value of 1.25 at 873 K. Furthermore, the reduced defect concentration and local stress concentration enhanced the mechanical properties (microhardness and Young's modulus) of the Cu_1.8S_0.97P_0.03. Thus, this study provides novel insights into the optimization of the thermoelectric properties of the Cu–S system and underscores its significant potential for application in other sulfide thermoelectric materials.