Influence of Ag doping on the microstructure and electrical properties of ZnO-Bi2O3-based varistor ceramics

Abstract

Silver in the form of AgNO 3 was added to ZnO-based varistor ceramics prepared by the solid-state reaction method. The effects of AgNO 3 on both the microstructure and electrical properties of the varistors were studied in detail. The optimum addition amount of AgNO 3 in ZnO-based varistors was also determined. The mechanism for grain growth inhibition by silver doping was also proposed. The results indicate that the varistor threshold voltage increases substantially along with the AgNO 3 content increasing from 0 to 1.5mol%. Also, the introduction of AgNO 3 can depress the mean grain size of ZnO, which is mainly responsible for the threshold voltage. Furthermore, the addition of AgNO 3 results in a slight decrease of donor density and a more severe fall in the density of interface states, which cause a decline in barrier height and an increase in the depletion layer.

TiO₂ Added Zn-Bi Based Varistors: Microstructure, I-V, Flow and Aging Characteristics

“…The values of φb, ω, Ns and Nd were calculated according to the grain boundary defect model [13,14], which the current density can be described by the following equation:…”

Microstructure Engineering to Drastically Reduce the Leakage Currents of High Voltage ZnO Varistor Ceramics

“…The exceptional capacity of the spinel grains to dissolve and incorporate other oxide additives makes this option more feasible: the spinel lattice is a fairly open structure that easily accommodates additional cations on its tetrahedral and octahedral empty sites . The fact is that for long, it has been monitored that oxides like Co, Mn, Ni, and particularly Cr, which are incorporated to enhance the varistor electrical nonlinearity and/or stability to degradation, also diffuse into the spinel grains and to some extent stabilize this phase against its expected decomposition to pyrochlore . But even so a certain amount of Py is yet obtained in the sintered samples, and the leakage current values are still elevated.…”