The structural model proposed by Dénès et al. implies that Ca 1-x Sn x F 2 exhibits both occupational cation disorder and Sn lone-pair orientational disorder, and similar behaviour might be expected in other mixed-cation fluorites where one cation species has a stereoactive lone pair . Such mixed-cation fluorites are interesting to examine in the context of understanding how these distinct but coexisting forms of host-framework disorder together modulate the structure and dynamics of the mobile anion species. Here, we focus on the structure and fluoride-ion dynamics of c-BaSnF 4 , which we consider a representative member of this family of mixed-cation fluorites. c-BaSnF 4 is also of practical interest due to its shared composition with the more widely-studied layered tetragonal phase t-BaSnF 4 , which is considered to be a prospective solid electrolyte for fluoride-ion batteries .