The preparation of a ZnO varistor doped with Pr6O11-CoO-Cr2O3-Y2O3-Al2O3 and its properties

ZnO varistors doped with Pr6O11-CoO-Cr2O3-Y2O3-Al2O3 were prepared at different sintering temperatures and their properties were investigated. The average grain size increased to 4.3-11.3μm with the increase of sintering temperature. However, the sintering temperature does not have an effect on the sintered density. The breakdown field greatly decreased from 6327 to 1974 V/cm, exhibiting a wide voltage gradient with the increase of sintering temperature. However, the nonlinear coefficient was almost unaffected by the sintering temperature: it was in the range 43.7-41.9. The varistor sintered at 1350∘C exhibited the highest stability against DC accelerated aging stress (0.95EB/150∘C/24h); the variation rates of breakdown field and nonlinear coefficient are −0.3% and −6.7%, respectively.