Scanning electron microscopy-based remote electron-beam induced current techniques were used to investigate the electrical characteristics of individual grain boundaries in an oxide-based varistor. Some boundaries exhibited bright and dark contrasts which were consistent with symmetrical opposed electric fields on each side of a charged grain boundary. Most interfaces were electrically asymmetrical, and exhibited only bright or dark contrast. In these cases, the application of an external bias voltage (some tens of mV) across the boundary was necessary in order to restore the symmetrical structure. The orientations of the grains, on each side of the grain boundaries which exhibited these contrast-types, were determined by using electron back-scattered diffraction analysis. The grain boundary plane orientation was established by using depth-resolved electron-beam induced current methods. It was found that the asymmetry in the electrical structure was governed by the orientations of the grain boundary planes on each side of the interface.

Crystal Plane Influence of the EBIC Contrast in Zinc Oxide Varistors. C.Leach: Journal of the European Ceramic Society, 2001, 21[10-11], 2127-30