antiCaF2

antiCaF2 refers to the antifluorite crystal structure, which is an inverse of the fluorite (CaF2) structure. In the standard fluorite structure, cations occupy lattice sites and anions occupy interstitial sites, with a specific stoichiometry. The antifluorite structure reverses this arrangement, where anions occupy the cation sites and cations occupy the anion sites.

This structural type is commonly observed in compounds with the stoichiometry M2X, where M is a metal (typically an alkali or alkaline earth metal) and X is a chalcogen or halogen (such as oxygen, sulfur, or fluorine). For instance, alkali metal oxides like Li2O and Na2O crystallize in the antifluorite structure. In these compounds, the oxygen anions occupy the positions typically held by calcium in CaF2, and the metal cations occupy the positions typically held by fluorine.

The antifluorite structure is cubic and belongs to the space group Fm-3m. It is characterized by a face-centered cubic (FCC) lattice of anions with cations located in half of the tetrahedral interstitial sites. The arrangement of ions within this structure leads to various physical properties, including ionic conductivity and dielectric behavior, which are of interest in materials science and solid-state chemistry. The term "antiCaF2" is used as a convenient shorthand to describe this structural inverse of the well-known fluorite mineral and its synthetic counterparts.