Effect of Pr_6O_(11) Doping on the Microstructural and Electrical Properties of ZnO-Pr_6O_(11)-Co_3O_4-Cr_2O_3-SnO_2 Varistors

摘要

ZnO-Pr_6O_(11)-Co_3O_4-Cr_2O_3-SnO_2 varistors with different doping levels of Pr_6O_(11) (0.25-2 mol%) were prepared at 1300°C with conventional ceramic processing, and the effect of Pr_6O_(11) doping on the microstructure and electrical properties of the varistor materials were investigated. The results indicated that the doped Pr_6O_(11) basically existed at the boundary of ZnO grains in the varistor ceramics, and SnO_2 might enter into the lattice of ZnO grains or precipitate in reaction with Pr_6O_(11) into Pr_2Sn_2O_7 at the gain boundaries particularly where there were three or more ZnO grains. The analysis of scanning electron microscopy further revealed that Pr_6O_(11) doping would inhibit the growth of ZnO grains, resulting in decreasing ZnO grain size with increasing doping level of Pr_6O_(11). The measured electric-field/current-density characteristics of the samples showed that the varistor voltage increased with increasing doping level of Pr_6O_(11) when the doping level was no more than 1.5 mol%, and the nonlinear coefficient of the varistors increased with increasing doping level of Pr_6O_(11) up to no more than 1.0 mol% in the varistors, respectively.