The nature of the surface charge on ionic crystals

Abstract

If it is assumed that in the neighbourhood of the surface of a crystal the chemical potentials of lattice defects are different from those in the bulk, a space charge is automatically formed in such a way that a positive or negative space-charge layer adjacent to the surface is compensated by a much thicker space-charge layer of opposite sign further away from the surface. In this paper it is shown how the charge distribution can be computed. When dopants of different valency are incorporated into ionic crystals the space-charge layers do change, and even a reversal of the sign of the space charge is possible. From measurements of the point of zero charge of doped and undoped AgBr, the various parameters have been computed.