Microstructural characteristics and grain growth kinetics of Pr6O11 Doped SnO2-based varistors

The effect of the addition of various amounts of Pr6O11 on the grain growth and densification process, microstructure, formation and distribution of secondary phases, and electrical properties of SnO2-based varistors containing cobalt and niobium oxides has been investigated. It has been observed that in the presence of as low as 0.1 mol% of Pr6O11, the formation of Pr2Sn2O7 can be detected using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The kinetics of grain growth in samples without and with praseodymium oxide has shown that increasing Pr6O11 from 0 to 0.5 mol%, changes the grain growth exponent from 2 to 6 and the activation energy from 350 kJ/mol to around 700 kJ/mol. This may be due to the cooperative effect of the secondary phases. The largest nonlinear coefficient, α, and the lowest leakage current, IL, has been observed for the sample containing 0.05 mol% Pr6O11 whereas the highest breakdown voltage has been recorded for the sample with 0.5 mol% Pr6O11.