INFLUENCE OF MICROSTRUCTURE AND GRAIN-BOUNDARY POTENTIAL BARRIER LAYER ON THE ELECTRICAL BREAKDOWN OF POSITIVE TEMPERATURE-COEFFICIENT BATIO3 CERAMICS

The influence of the microstructure and the grain boundary potential barrier layer on the electrical breakdown of barium titanate positive temperature coefficient (PTC) ceramics was studied. Samples of various grain sizes were prepared by adjusting the amount of Sb substitution into Ba sites in barium titanate PTC ceramics. Samples exhibiting large PTC effect (R(max)/R(min)) and fine grain size withstand high applied voltage. It is clarified that grain size effect is related to the number of grain boundaries per unit thickness of the samples because the applied voltage drop is mainly across the potential barriers at grain boundaries. However, the voltage dependence of a single grain boundary potential barrier was more important in determining breakdown voltage in our study. The voltage dependence of the grain boundary potential barrier layer was due to the grain boundary built-in potential.