The structures of inorganic crystals: A rational explanation from the chemical pressure approach and the anions in metallic matrices model

Abstract

This chapter deals with the chemical principles that govern the structure of those inorganic crystals that are commonly described in terms of ionic constituents. Rock-salt, cesium chloride, zinc blende, fluorite, rutile, perovskite, spinel, elpasolite, … and most of the important structures in Mineralogy and Crystal Chemistry constitute examples where these chemical principles are of application. Crystal Chemistry puts the emphasis on the description of inorganic crystals using cation-centered coordination polyhedra. These basic building blocks are transferable among different compounds and work similarly to functional groups in Organic Chemistry, thus providing a wealth of structure-property relationships that allows us to better understand the behavior of materials under general external stimuli. To complement and support this perspective, we focus in this chapter on the underlying reasons that explain why an inorganic compound shows its specific crystalline structure. Two simple chemical principles will be introduced. The first one states the linking between the actual positions of anions in inorganic crystals and their corresponding sub-lattice metallic arrays. The second principle illustrates how the electronegativity concept is key to determine the extent of the strains induced by the non-metallic atoms in the metallic sub-lattice. A very intuitive formalism called Chemical Pressure, and derived from the Density Functional Theory approximation, serves as the general framework to elaborate our view.