High Ductility and Excellent Thermoelectric Performance in Te-Stabilized Cubic Ag 2 Te x S 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.