Many electroceramics derive their technologically useful and scientifically appealing properties through electrically active grain boundaries (GBs). Examples of such properties include traditional nonlinear current-voltage relationship (i.e. varistor behavior) and positive temperature of coefficient of resistance (PTCR effect), to recently “rediscovered” phenomena of space-charge formation across functional interfaces, including ferroeletric thin films.
In many such cases, the transport of charge across these interfaces is mediated through potential barriers which form at the core of these interfaces. For example, varistor behavior is attributed to formation of Schottky barriers at GBs which modify the transport of electrons, leading to the nonlinearity in I-V characteristics. The formation of Schottky barrier at the GB core, in turn, is attributed to the formation of space-charge across GBs. The formation of space-charge, further, is clearly attributable to decoration of GB core with charged defects with compensating opposite charge across the GB. The presence, sign, magnitude and spatial distribution of space-charge form the key to understand the Schottky barriers, thus the transport properties of interfacial systems.