High Thermoelectric Figure of Merit Achieved in Cu 2 S 1- x Te x Alloys Synthesized by Mechanical Alloying and Spark Plasma Sintering

• Published in: ACS applied materials & interfaces Vol. 10; no. 38; pp. 32201 - 32211
• Main Authors: Yao, Yao, Zhang, Bo-Ping, Pei, Jun, Sun, Qiang, Nie, Ge, Zhang, Wen-Zhen, Zhuo, Zhen-Tao, Zhou, Wei
• Format: Journal Article
• Language: English
• Published: United States 26.09.2018
• Subjects: mechanical alloying; Cu2S; thermoelectric; spark plasma sintering; Cu2Te
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.8b11300

Chalcogenides have been considered as promising thermoelectric materials because of their low cost, nontoxicity, and environmental benignity. In this work, we synthesized a series of Cu S Te (0 ≤ x ≤ 1) alloys by a facile, rapid method of mechanical alloying combined with spark plasma sintering process. The Cu S Te system provides an excellent vision of the competition between pure phase and phase transformation, entropy-driven solid solution, and enthalpy-driven phase separation. When the Te concentration increases, the Cu S Te system changed from the pure monoclinic Cu S at x = 0 to monoclinic Cu S Te solid solution at 0.02 ≤ x ≤ 0.06 and then transforms to hexagonal Cu S Te solid solution at 0.08 ≤ x ≤ 0.1. The phase separation of hexagonal Cu Te in the hexagonal Cu S matrix occurs at 0.3 ≤ x ≤ 0.7 and finally forms the hexagonal Cu Te at x = 1. Owing to the changed band structure and the coexisted Cu S and Cu Te phases, greatly enhanced power factor was achieved in all Cu S Te (0 < x < 1) alloys. Meanwhile, the point defect introduced by the substitution of Te/S atoms strengthened the phonon scattering, resulting in a lowered lattice thermal conductivity in most of these solid solutions. As a consequence, Cu S Te exhibits a maximum ZT value of 1.18 at 723 K, which is about 3.7 and 14.8 times as compared to the values of pristine Cu S (0.32) and Cu Te (0.08), respectively.