Abstract
ZnO-Pr6O11-Co3O4-Cr2O3-SnO2 varistors with different doping levels of Pr6O11 (0.25-2 mol%) were prepared at 1300 °C with conventional ceramic processing, and the effect of Pr6O11 doping on the microstructure and electrical properties of the varistor materials were investigated. The results indicated that the doped Pr6O11 basically existed at the boundary of ZnO grains in the varistor ceramics, and SnO2 might enter into the lattice of ZnO grains or precipitate in reaction with Pr6O11 into Pr2Sn2O7 at the gain boundaries particularly where there were three or more ZnO grains. The analysis of scanning electron microscopy further revealed that Pr6O11 doping would inhibit the growth of ZnO grains, resulting in decreasing ZnO grain size with increasing doping level of Pr6O11. The measured electric-field/current-density characteristics of the samples showed that the varistor voltage increased with increasing doping level of Pr6O11 when the doping level was no more than 1.5 mol%, and the nonlinear coefficient of the varistors increased with increasing doping level of Pr6O11 up to no more than 1.0 mol% in the varistors, respectively.
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