Synthesis by Hydrothermal Treatment of ZnO-Based Varistors Doped with Rare Earth Oxides and Their Characterization by Impedance Spectroscopy

ZnO-based ceramic varistors have shown excellent electrical and dielectric properties due to their characteristics microstructures represented by the arrangement of their grains and grain boundaries that allow the absorption and flow of energy when subjected to an electrical surge. Their properties and characteristics depend on their chemical compositions and processing routes. Typical processing routes involve several stages of grinding and precalcination—which are time consuming processes. Because of this, this study proposes a simpler and cheaper alternative route for processing ceramic varistors. The alternative process proposed is the mixing of the precursor oxides by means of a hydrothermal treatment. The characteristics and properties of the synthesized ceramic varistors were evaluated by means of scanning electron microscopy, X-ray diffraction and impedance spectroscopy, considering the effect of the addition of rare earth oxides (La2O3, CeO2 and Nd2O3). The results showed that the mixing of the oxides through hydrothermal treatment produces ceramic varistors with characteristics and properties similar to those obtained by other processing routes. Furthermore, it was observed that the addition of rare earth oxides affects the characteristics and properties of the ceramic varistor depending on the type of rare earth oxide added, its concentration and ionic radius.

Donor Solid Solubility and Microstructure of Nb-Doped TiO2 Ceramic Varistor

In this paper, the effect of sintering temperature on microstructure and donor solid solubility of Nb-doped TiO2 varistor ceramic is investigated. SEM and EDXS were carried out to study the microstructure and chemical compositions of TiO2 grain. The results show that the TiO2 sample sintered at 1350°C have better microstructure and properties. The grains size of the TiO2 sample is about 15μm and solid solubility of donor Nb 5+ cation solute in TiO2 grains is 1.49mol%.

ZnO-Pr6O11-Co3O4-TiO2-Based Ceramic Varistor Materials

The preparation and characterization of ZnO-Pr6O11-Co3O4-TiO2 (ZPCT) based varistor materials with different doping levels of TiO2 and Pr6O11 were investigated. The results reveal that: (1) TiO2 is an important additive, acting as an inhibitor of ZnO grain growth. The doping of appropriate amount of TiO2 can significantly improve the nonlinear properties and decreases the leakage current of the varistors, achieving a relatively high nonlinear exponent and low leakage current with 1.0 mol% TiO2 doped. (2) The oxide of Pr6O11 microstructurally plays the role of inhibition in grain growth. The doping of appropriate amount of Pr6O11 can improve the nonlinear property, and decrease the leakage currents of the varistors, acquiring the optimum results with 1.5 mol% Pr6O11 doped.