Point defects as acid-base active particles in ionic crystals

Point defects such as excess ions or ion vacancies (together with excess electrons and holes as the electronic excitations) enable the solid to react to outer chemical and electrical excitations. They are not only the mobile ionic constituents, they are also the relevant acid-base active particles with respect to reactivity. It is in particular this latter aspect that is not adequately appreciated in the literature. A recently developed concept based on point defects [1] is able to provide an objective, testable and thermodynamically valuable ionotropic acid-base concept for solids. The concept also allows one to unify bulk and surface acidity/basicity. These points are discussed in conjunction with the important role of point defects in reaction kinetics and catalysis.