Grain growth kinetics and electrical properties of CuO doped SnO2-based varistors

Up to now, attempts for developing coarse-grained SnO2-based varistors which exhibit high nonlinearity property at lower voltage have become a challenge without any prominent result because of its unknown grain growth mechanism. In this study, the effect of CuO addition to SnO2-based varistors as a grain growth enhancer additive on microstructural development, grain growth kinetics, and electrical properties was investigated. The characterization of grain growth kinetics showed that CuO addition encouraged grain growth and enhanced the grains size as it could be seen in the activation energy which decreased from 594 kJ/mol to 364 kJ/mol. In the samples with a low amount of CuO, the solute drag force is the controlling mechanism of grain growth. By further addition, the mechanism changed to the Sn4+ solution-precipitation in CuO-rich liquid phase. Also, the electrical properties of CuO doped samples showed that they are so promising for low voltage applications. (C) 2018 Elsevier B.V. All rights reserved.