Influence of Intrinsic Trapping on The Performance Characteristics of ZnO-Bi2O3Based Varistors

The lumped parameter/complex plane analysis technique reveals several contributions to the ac small-signalterminal immittance of the ZnO-Bi2O3 based varistors' grain-boundary response. The terminalcapacitance constitutes multiple trapping phenomena, a barrier layer contribution, and a resonanceeffect in the frequency range 10-2 ≤ f ≤ 109 Hz. A trapping response near to ∼105 Hz (∼10-6 s),observed via the loss-peak and a distinct depressed semicircular relaxation in the complex capacitanceplane, is common to all well-formed (exhibiting good performance for applications) devices regardlessof the composition recipe and processing route. This trapping is attributed to possible formation ofionized intrinsic or native defects, and believed to be predominant within the electric field falling regionsacross the microstructural grain-boundary electrical barriers. The nature of rapidity of this intrinsictrapping and the corresponding degree of uniformity/non-uniformity can be utilized in conjunction withrelevant information on other competing trapping phenomena to assess an overall performance of thesedevices. The constituting elements, responsible for the average relaxation time of the intrinsic trapping,indicate some sort of possible surge arrester (i.e., suppressor/absorber) applications criteria in thepower systems' protection. The factors related to materials' history, composition recipe, and processingvariables influence or modify relative magnitudes and increase or decrease the visibility of the constitutingelements without distorting devices' generic dielectric behavior