Changing Polyhedral Connectivity through Sulfide Introduction in an Ionically Conducting Na–Ta–Cl–S Mixed Anion System

Mixed-anion strategies have proven effective in designing materials with diverse functionalities, particularly for enhancing the ionic conductivity in sodium halides. While prior efforts have largely focused on incorporating oxide anions into halide frameworks, the exploration of other anions, such as sulfides, has recently begun. According to Pauling’s third rule, highly charged cations disfavor ordered edge- or face-sharing polyhedra, making mixed-anion substitution an effective route to promote the structural disorder needed for fast Na + transport. Here, we contribute to these emerging efforts by investigating sulfide incorporation in amorphous Ta 5+ containing Na–halide frameworks. Furthermore, we reveal the formation of an amorphous matrix with structural motifs distinct from those of oxychlorides. These unique features facilitate Na + transport, achieving room-temperature ionic conductivity of 3.8 mS·cm –1 .