Fluorosulfide La_2+<i>x</i>Sr_1–<i>x</i>F_4+<i>x</i>S₂ with a Triple-Fluorite Layer Enabling Interstitial Fluoride-Ion Conduction

Fluoride-ion conducting solid materials are applicable as electrolytes for sensing devices and next-generation rechargeable batteries. Most of the previously reported have been limited to single-anion compounds such fluorite-type, tysonite-type, perovskite-type structures. These suffered from further improvements by crystal structure modification which derives a paradigm shift in material tailoring. Fluoride sulfide ions prefer respective coordination environments because different ionic radii electronegativity. This feature implies that fluorosulfide mixed-anion potential form anion-ordering structures with new fluoride-ion layers. Herein, we found La2+xSr1–xF4+xS2 exhibits conduction. The presence multiple anions results formation an two-dimensional lattice triple fluorite layers, cannot be realized metal fluorides. Sulfide increase number interstitial sites fluoride ions, forming conduction pathway.