Stabilizing superionic Ag2S1-xTex phase to room temperature via S/Te size disparity

Superionic β -Ag 2 S demonstrates exceptional ionic conductivity and ductility, rendering highly promising for applications in electrochemical sensors, thermoelectric devices and solid-state electrolytes. However, it is still haunted by the limited thermodynamic stability, transitioning to the poorly conductive α -Ag 2 S phase upon cooling to room temperature (RT). Herein, a solid solution formed by partial isovalent substitution of sulfur with tellurium stabilizes the superionic phase via the substantial atomic-size mismatch between S and Te. Specifically, Ag 2 S 1-x Te x (0.2 ≤ x ≤ 0.8) maintain superionic phase at RT without observable phase transition upon cooling. This stabilized superionic phase originates from the substantial size mismatched between S and Te. Furthermore, the anion disorder caused by the local volume expansion introduced by large-radius Te reduces the activation energy the activation energy barrier and provides more vacancies for Ag + ion transportation. This work confirms the efficiency of crystal amorphization strategy for stabilizing high-temperature superionic phases at ambient conditions, enabling the development of superionic conductors.