Ionic radii in fluorites

Abstract

The construction of the fluorite unit-cell from the ionic radii of the constitutive species is proposed with the use of our hybrid model, considering flexible anion and cation radii. 24 binary and stoichiometric compounds crystallizing in this structure were investigated to find an empirical correlation between the anion's radius as a function of the cation's size that can be used to evaluate the lattice parameter of new fluorite-structured ionic crystals. This method was applied to the binary dioxides and difluorides that crystallize in the fluorite structure at room temperature and atmospheric pressure. The relevance of our model was also enlarged to complex oxide solid-solutions incorporating aliovalent cations, namely uranium dioxides doped with trivalent cations (U,M)O2 with M = Y(III), La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Dy(III), Ho(III), Er(III), and Lu(III).