CaF2type

The CaF2-type is a crystallographic structure type named after calcium fluoride. It describes a class of compounds with the general formula AB2 in which the A2+ cations form a face-centered cubic (fcc) lattice and the B− anions occupy all tetrahedral interstitial sites within that lattice. This arrangement yields a highly symmetric cubic structure, commonly referred to as the fluorite structure.

In the CaF2-type structure, the A cations are eightfold coordinated by the B anions, while each B anion is fourfold coordinated by A cations. The conventional unit cell contains 4 A cations and 8 B anions, giving the empirical formula AB2. The space group is typically Fm-3m (cubic), and the lattice is described as an fcc array of cations with B anions filling the tetrahedral holes.

Common members of this structure type include CaF2 itself and many fluorite-derivative oxides such as CeO2 (ceria), ThO2, ZrO2, and UO2. In these materials, the same basic cation framework holds, though the presence of vacancies, dopants, or temperature changes can influence symmetry, defect chemistry, and properties such as ionic conductivity.

Key properties associated with CaF2-type materials are characteristic of ionic solids: high melting points, robust thermal stability, and strong ionic bonding. The structure also serves as a precursor to related phases and defect-fluorite derivatives, which are studied in solid-state chemistry and materials science for catalysis, nuclear materials, and ionic conduction applications.

Overall, the CaF2-type provides a simple, highly symmetric framework for a wide range of compounds, with the fluorite structure acting as a common reference point in crystallography and materials research.