Phase-modulated mechanical and thermoelectric properties of Ag₂S_1-xTe_x ductile semiconductors

By virtue of the excellent plasticity and tunable transport properties, Ag₂S-based materials demonstrate an intriguing prospect for flexible or hetero-shaped thermoelectric applications. Among them, Ag₂S_1-xTe_x exhibits rich and interesting variations in crystal structure, mechanical and thermoelectric transport properties. However, Te alloying obviously introduces extremely large order-disorder distributions of cations and anions, leading to quite complicated crystal structures and thermoelectric properties. Detailed composition-structure-performance correlation of Ag₂S_1-xTe_x still remains to be established. In this work, we designed and prepared a series of Ag₂S_1-xTe_x (x = 0–0.3) materials with low Te content. We discovered that the monoclinic-to-cubic phase transition occurs around x = 0.16 at room temperature. Te alloying plays a similar role as heating in facilitating this monoclinic-to-cubic phase transition, which is analyzed based on the thermodynamic principles. Compared with the monoclinic counterparts, the cubic-structured phases are more ductile and softer in mechanical properties. In addition, the cubic phases show a degenerately semiconducting behavior with higher thermoelectric performance. A maximum zT = 0.8 at 600 K and bending strain larger than 20% at room temperature were obtained in Ag₂S_0.7Te_0.3. This work provides a useful guidance for designing Ag₂S-based alloys with enhanced plasticity and high thermoelectric performance.