An AFM/EFM Study of the Grain Boundary in ZnO-Based Varistor Materials

Zinc oxide (ZnO)‐based varistors are metal oxide varistors whose nonlinear properties are characterized by electrical resistance that decreases as the applied field increases. The multiphasic nature of varistors leads to the formation of Schottky barriers, which are responsible for the materials' nonlinear behavior. The objective of this work was to image the potential barriers in ZnO doped with 0.5 mol% Cu and x wt% G (G is a frit and x=0, 1, and 5 wt%). The frit served to form a glassy insulating layer around the grain boundaries. Samples were sintered at 1050°C and the microstructures were analyzed using a Nanoscope IIIa atomic force microscope. The results of the electric force microscopy experiments map the electric field distribution on the surface of CuO–ZnO‐based ceramics.