Zinc oxide varistors

Abstract

inc oxide varistors are novel semiconducting ceramics having highly non-ohmic current-voltage characteristics, which originate at the grain boundaries. These varistors are widely utilized in protecting electric power lines and electronic components against dangerous voltage surges. This overview of zinc oxide (ZnO) varistors includes electrical characteristics, fabrication methods, effects of additives, grainboundary properties, and specific applications.

Electrical degradation of double-Schottky barrier in ZnO varistors

“…80 The occurrence and stabilization of Bi 2 O 3 of certain phase is closely related to other elements co-doped 81 and depends on process conditions like annealing treatment. 5 It is known that δ-Bi 2 O 3 is a faster oxygen-ion conductor, and the β phase is much more oxygen-conductive than the γ phase, 28 which could lead to the speculation concerning its role as stabilizaing/destabilizing the ZnO varistor. Recently, M. Takada et al 82 have investigated the two types of Bi 2 O 3 deposit (sheet-like and spot-like, as seen in FIG.…”

“…Bi 2 O 3 doped with potassium exhibits superconductivity, and hence we cannot drop conclusion on its precise effect on DSB degradation until more atomic-scale investigations are presented which are currently lacked due to the difficulties in theoretical modeling of corresponding systems that are also computationally demanding. Fortunately, some excellent review papers 5,28 have provided discussions, though insufficient, on the role of Bi 2 O 3 which could help for a better understanding.…”

“…This will, as discussed previously, inevitably decrease the density of complex defect at grain boundary region and thus deteriorate the acceptor-like interfacial states, thus destabilizing and lowering the Schottky barrier. Such oxygen desorption and barrier degradation process can be mainly ascribed to two reasons, the effect of electrical stress and the gradient of oxygen-defect concentration 28 at grain boundary region.…”

“…non-monotonic ageing behavior of DSB 26,28 barrier at early stage of degradation, 28 extended Gupta and Carlson's model 13,48,49 should be inevitably mentioned here, where the role of intergranular phases are taken into consideration additionally. Such extended model centers on the charged particles (FIG.…”

“…16 The change in the value of dielectric constant directly leads to the change of capacitance of varistor 27,28 indicating the complexity of ageing in ZnO varistor under the effect of long-term operation voltage.…”