Location and orientation of lone pairs in apatite-type materials: a computational study.

Electron localisation function (ELF) calculations have been used to provide the first computational location of the cation lone pairs in apatite materials. We show that the orientation of the lone pairs varies depending on the identity and positions of the channel anions. The results represent a new platform for interpreting experimentally observed structure-property relationships in functional apatites. In particular, they have significant implications for ionic conductivity and suggest that structure-property relationships in lone-pair containing apatite-type solid electrolytes are more complex than previously thought.