POINT-DEFECTS AND TRANSPORT IN NONSTOICHIOMETRIC OXIDES - SOLVED AND UNSOLVED PROBLEMS

First, the basic concepts used in the area of defects and transport in non-stoichiometric oxides are reviewed. Their capabilities and shortc omings are addressed, including the problems of dealing appropriately with point defects at higher defect concentrations and with situations where more than one sublattice is available for one type of ion. As a n example of where ideal solution point defect thermodynamics can be a pplied without much problems, the iron oxide magnetite, Fe3-deltaO4, i s discussed. The cation diffusion in this material is also reviewed. T hen some magnetite-based solid solutions are briefly discussed with re gard to their defect chemistry and the transport of cations. Finally, two largely ignored topics are addressed: (i) the influence of the val ence state of an ion on its diffusivity, and (ii) contributions from n ear-boundary regions to the variation of the oxygen content of nonstoi chiometric oxides. (C) 1998 Elsevier Science Ltd. All rights reserved.