Influence of distribution of additives on electrical potential barrier at grain boundaries in ZnO-based multilayered chip varistor

The influence of the distribution of additives on the electrical potential barrier at grain boundaries in a ZnO-based multilayered chip varistor was investigated by scanning surface potential microscopy (SSPM) and transmission electron microscope (TEM). The leakage current strongly depended on the distribution of additives, and a more uniform distribution improved the electrical nonlinearity. SSPM images revealed that the grain-boundary resistance of a uniformly distributed sample was higher than that of a poorly distributed sample. The decrease in the electrical nonlinearity due to the poor distribution was attributed to a decrease in the potential barrier height instead of an increase in the inactive grain boundary. The TEM analysis indicated that the poor distribution of Pr ions interfered with the formation of the potential barrier and resulted in the decrease in its height.