Abstract
The electrical and microstructural properties of a series of ZnO -based thick film varistors (TFVs) doped with 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10 mol% Y 2 O 3 were studied. It was found that sample doped with 0.08 mol% Y 2 O 3 showed the highest potential gradient of 3159.4 V/mm with a leakage current of 36.4 μA and a nonlinear exponent of 13.1. The ZnO grain size decreased with increasing Y 2 O 3 content, which was the origin for the increase in potential gradient. Raman spectra results showed that the tensile stress increased linearly with Y 2 O 3 doping. Larger tensile stress was considered to result from the lattice distortion and inevitably influenced the grain boundary characteristics. While the Y 2 O 3 doping concentration was beyond 0.08 mol%, the effect of residual stress on electrical properties was much more remarkable than that of grain size, leading potential gradient to be weakened. As a result, high potential gradient of ZnO -based TFVs could be obtained with Y 2 O 3 doping concentration of 0.08 mol% and qualified as excellent candidates for high voltage varistor application.
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