Highly stable nonlinear behavior against impulse current of ZnO–Pr6O11–CoO–Cr2O3–Y2O3 varistors

The nonlinear electrical behavior against the impulse stress (400–1200 A) in the ZnO–Pr6O11–CoO–Cr2O3–Y2O3 varistors has been investigated with sintering time. The sintering time did have a significant effect on the clamp ratio, which exhibits a surge protection capability. The varistors sintered for 1 h exhibited the best clamp characteristics, in which the clamp voltage ratio was in the range of K = 1.61–1.92 at a lower impulse current region (5–50 A) and was in the range of K = 2.06–2.55 at a higher single impulse current region (400–1200 A). The best electrical stability against the multi-impulse aging stress of 1200 A was also obtained from the varistors sintered for 2 h, where %ΔE1 mA =−1.6%, %Δα =1.3%, and %ΔJL =−4.9%.