Transport in electroceramics: micro- and nano-structural aspects

Point defects are of paramount importance for electroceramics. They are key structure elements as regards materials functionality; but, in addition, they are also decisive for chemical kinetics, hence for preparation, conditioning, annealing and degradation phenomena. Concentrations and mobilities of these charge carriers are significantly changed at or near interfaces (or more generally higher dimensional defects) giving rise to depletion, accumulation, and inversion layers with respect to ionic and electronic carriers and hence to distinct electrical and chemical effects. It is discussed how these effects can be explained and how such knowledge can be used to design electroceramics purposefully. Examples refer to ionically or mixed conducting oxides and halides. Finally, in nano-structured materials the spacing of interfaces becomes relevant in that local properties can be severely affected. Such size effects do not only lead to confinement effects in the case of electronic carriers but also to anomalies with respect to ion conduction and mass transport. The potential of the nano-regime for electrical and chemical properties of electroceramics is discussed in the framework of a "soft materials science". (C) 2003 Elsevier Ltd. All rights reserved.