In polycrystalline materials the trapping of charge at interfaces has a decisive influence on the electrical transport properties through the formation of electrostatic potential barriers. This can either be an intrinsic phenomenon or can be related to impurity segregation leading to complex defect centers. This plays a key role in technologically important systems, especially those having electrically active interfaces, e.g.,p-n junctions in semiconductors and grain boundaries in electroceramics.
Electroceramic oxides such as ZnO and SrTiO3 are common systems that exhibit the tendency of current control by internal potential barriers. While bulk measurements, either electrical (e.g. P-E, C-V, I-V), or optical (e.g. Raman) have contributed significantly to the understanding of charged interfaces, there are a very few direct observations of electrical activity at a nanometer level. For instance, it has been recognized that space charge and dopant segregation at the grain boundary are inter-related.