Rotational Stacking Faults in the Ionic Conductor Li₃ScCl₆

Halide-based solid electrolytes have gained recent interest due to their promising ionic conductivity and wide electrochemical stability window, but the influence of synthesis conditions on structure is not fully characterized. Here, we report a combined experimental and computational study of the effect of thermal treatment temperature on the structure and Li⁺ conduction dynamics of the superionic halide Li₃ScCl₆. Synchrotron diffraction analysis shows that samples treated between 450 °C and 750 °C form the monoclinic Li3ScCl6 structure and contain rotational stacking faults, whose density increases with thermal treatment temperature and mechanical processing time. Impedance spectroscopy, nuclear magnetic resonance spectroscopy, and molecular dynamics simulations using machine-learned interatomic potentials, however, indicate that these faults have a negligible effect on long-range Li+ conductivity, though local Li⁺ dynamics are modified. This work demonstrates that Li₃ScCl₆ maintains robust transport properties despite rotational stacking faults, and highlights the importance of in-depth structural analyses for understanding the relationships between synthesis protocols, structure, and ionic transport in halide solid electrolytes.