EQUILIBRIA AND ELECTRONIC PROCESSES

The operation of solid-state gas sensors and of certain types of catalyst depends on the energy of free carriers in one phase relative to some state in another medium. Here special problems arise in determining the electron affinity of ionic crystals. These are discussed, together with some of the issues which cause similar problems in different types of systems, here including aqueous solutions and conducting polymers. For ionic solids, knowledge of which charge states are stable for substitutional transition metal ions gives a powerful tool, giving predictions in accordance with electrochemical data. It appears that MgO has a negative electron affinity. © 1993 Academic Press, Inc.