Classification of heavy metal fluorides. Fluorides with 'fluorite-like' cation arrangement

Four families of crystallographic planes with dense trigonal cation lattices which are mutually oriental as the faces of a regular octahedron are the principal feature of structure type fluorite. The complication of the cation composition can result in the tetragonal one. Geometrical parameters of the cation sublattice remain rather stable and close to a perfect cubic face-centered cation sublattice of the fluorite (measure of similarity 1.00-0.81) for all analysed structures of fluorides and certain oxyfluorides of U4+, Th4+, Zr, Ln. It confirms the concept that the crystal stable in governed by the systems of parallel planes with dense lattices of heavy atoms. 24 refs., 5 figs., 1 tab