Percolation effects in dc degradation ofZnOvaristors

Abstract

For quantitative estimation of the degree of electrical disorder (electrical inhomogeneity) in ZnO varistor ceramics caused by a variation in the barrier height at different grain boundaries in a sample, the comparison of threshold electric fields (onsets of highly nonlinear current-voltage characteristics) in ceramics and single grain boundary (GB) is suggested and approved. At dc degradation similar behavior of the current-voltage characteristics of ZnO varistor ceramics and single GB is observed. The percolation model of Shklovskii-De Gennes is applicable for the description of a disorder in ZnO varistor ceramics. The degree of the disorder in ZnO varistor ceramics is not dependent on the duration of dc degradation at least at degradation time below 60 h. At voltages close to the onset of a highly nonlinear region of current-voltage characteristic the correlation radius of infinite cluster is $ 5 times greater than the average grain size.

Electrical properties of structures based on varistor ceramics and polymer nanocomposites with carbon filler

“…Thus, the value of V U is insufficient for the breakdown or quick degradation of the varistor layer. 3,16 This result indicates that the considered two-layer structure based on varistor ceramics and polymer nanocomposites with carbon Fig. 3.…”

Distinct degradation processes in ZnO varistors: reliability analysis and modeling with accelerated AC tests

“…Long-term stresses cause degradation, along with a change in barrier height and characteristics due to the migration of ionized donors in the electric field and their redistribution in the near-surface region of the grains. This results in an increase in leakage current and, relevantly, a decrease in Vv [25]. Other possible mechanisms of deformation of grain boundary barriers explain different processes of degradation in ZnO varistors.…”

Quality Assessment of Low Voltage Surge Arresters

“…In the breakdown region the I(U) characteristic exhibit a strong nonlinearity, which is a result of a degradation process caused by a tunneling phenomenon between a conduction bands of neighboring ZnO crystallites [6]. This process is promoted by a shrinkage of grain boundaries as a consequence of a redistribution of donors in a space charge area with a reverse bias [7]. Conduction of significant current surges in weakened areas causes shrinkage of ZnO grains and modification of the chemical composition of the interfaces [8], which affects the electric parameters of the varistor [9].…”