Optimal performance of Cu1.8S1−xTex thermoelectric materials fabricated via high-pressure process at room temperature

Cu 1.8 S has been considered as a potential thermoelectric (TE) material for its stable electrical and thermal properties, environmental benignity, and low cost. Herein, the TE properties of nanostructured Cu 1.8 S 1− x Te x (0 ⩽ x ⩽ 0.2) bulks fabricated by a facile process combining mechanical alloying (MA) and room-temperature high-pressure sintering (RT-HPS) technique were optimized via eliminating the volatilization of S element and suppressing grain growth. Experimentally, a single phase of Cu 1.8 S was obtained at x = 0, and a second Cu 1.96 S phase formed in all Cu 1.8 S 1− x Te x samples when 0.05 ⩽ x ⩽ 0.125. With further increasing x to 0.15 ⩽ x ⩽ 0.2, the Cu 2− z Te phase was detected and the samples consisted of Cu 1.8 S, Cu 1.96 S, and Cu 2− z Te phases. Benefiting from a modified band structure and the coexisted phases of Cu 1.96 S and Cu 2− z Te, the power factor is enhanced in all Cu 1.8 S 1− x Te x (0.05 ⩽ x ⩽ 0.2) alloys. Combining with a drastic decrease in the thermal conductivity due to the strengthened phonon scatterings from multiscale defects introduced by Te doping and nano-grain boundaries, a maximum figure of merit ( ZT ) of 0.352 is reached at 623 K for Cu 1.8 S 0.875 Te 0.125 , which is 171% higher than that of Cu 1.8 S (0.130). The study demonstrates that doping Te is an effective strategy to improve the TE performance of Cu 1.8 S based materials and the proposed facile method combing MA and RT-HPS is a potential way to fabricate nanostructured bulks.