Fluorosulfide La <sub> 2+ <i>x</i> </sub> Sr <sub> 1– <i>x</i> </sub> F <sub> 4+ <i>x</i> </sub> S <sub>2</sub> with a Triple-Fluorite Layer Enabling Interstitial Fluoride-Ion Conduction
Shintaro Tachibana, Chengchao Zhong, Kazuto Ide, Hisatsugu Yamasaki, Takeshi Tojigamori, Hidenori Miki, Takashi Saito, Takashi Kamiyama, Keiji Shimoda, Yuki Orikasa
Abstract
High Resolution Image Download MS PowerPoint Slide Fluoride-ion conducting solid materials are applicable as solid electrolytes for sensing devices and next-generation rechargeable batteries. Most of the previously reported materials have been limited to the single-anion compounds such as fluorite-type, tysonite-type, and perovskite-type structures. These suffered from further improvements by crystal structure modification which derives a paradigm shift in the material tailoring. Fluoride and sulfide ions prefer respective coordination environments because of the different ionic radii and electronegativity. This feature implies that fluorosulfide mixed-anion compounds have potential to form anion-ordering crystal structures with new fluoride-ion conducting layers. Herein, we have found that the fluorosulfide La 2+ x Sr 1– x F 4+ x S 2 exhibits fluoride-ion conduction. The presence of multiple anions results in the formation of an anion-ordering two-dimensional crystal lattice with triple fluorite layers, which cannot be realized for metal fluorides. Sulfide ions in the crystal structure increase the number of interstitial sites of fluoride ions, forming a fluoride-ion conduction pathway.