High Ductility and Excellent Thermoelectric Performance in Te-Stabilized Cubic Ag₂Te_xS_1–x Solid Solutions

The stabilization at low temperatures of the Ag 2 S cubic phase could afford the design of high-performance thermoelectric materials with excellent mechanical behavior, enabling them to withstand prolonged vibrations and thermal stress. In this work, we show that the Ag 2 Te x S 1– x solid solutions, with Te content within the optimal range 0.20 ≤ x ≤ 0.30, maintain a stable cubic phase across a wide temperature range from 300 to 773 K, thus avoiding the detrimental phase transition from monoclinic to cubic phase observed in Ag 2 S. Notably, the Ag 2 Te x S 1– x (0.20 ≤ x ≤ 0.30) samples showed no fractures during bending tests and displayed superior ductility at room temperature compared to Ag 2 S, which fractured at a strain of 6.6%. Specifically, the Ag 2 Te 0.20 S 0.80 sample demonstrated a bending average yield strength of 46.52 MPa at 673 K, significantly higher than that of Ag 2 S, whose bending average yield strength dropped from 80.15 MPa at 300 K to 12.66 MPa at 673 K. Furthermore, the thermoelectric performance of the Ag 2 Te x S 1– x (0.20 ≤ x ≤ 0.30) samples surpassed that of both InSe and pure Ag 2 S, with the Ag 2 Te 0.30 S 0.70 sample achieving the highest ZT value of 0.59 at 723 K. These results indicate substantial potential for practical applications due to enhanced durability and thermoelectric performance.