Effect of cooling rate on degradation characteristics of ZnO·Pr 6O 11·CoO·Cr 2O 3·Y 2O 3-based varistors
The effect of cooling rate on microstructure, V- I characteristics, dielectric characteristics, and their degradation characteristics against DC stress of varistors composing of ZnO·Pr 6O 11·CoO·Cr 2O 3·Y 2O 3-based ceramics was investigated in the range of 2-8 °C/min. The cooling rate affected the electrical properties, whereas particularly DC degradation characteristics. The highest nonlinearity, with nonlinear exponent of 56.8 and leakage current of 1.6 μA was obtained from a cooling rate of 2 °C/min. However, the best degradation characteristics were obtained at a cooling rate of 4 °C/min. The stability against DC stress with cooling rate was found to be increased gradually in order of 8→2→6→4 °C/min in cooling rate. As a result, the degradation characteristics of varistors can be improved by changing the cooling rate.