The Structure of Solids

· Stable coordination depends upon the cation to anion radius ratio and the diagram shows the stable coordination numbers expected for various radius ratios.
· Frequently in ceramic structures, the Anions (-) form close-packed fcc or hcp arrays with the Cations (+) using Interstitial sites in these structures to provide overall charge neutrality of the crystal.
· This observation provides another way to think of these structures in terms of coordination polyhedra.

After: Kingery et al, "Introduction to Ceramics," Wiley (1976)