The preparation of a ZnO varistor doped with Pr6 O11-CoO-Cr2O3-Y2O3-Al2O3 and its properties

ZnO varistors doped with Pr-6 O-11-CoO-Cr2O3-Y2O3-Al2O3 were prepared at different sintering temperatures and their properties were investigated. The average grain size increased to 4.3-11.3 mu m 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 degrees C exhibited the highest stability against DC accelerated aging stress (0.95 E-B/150 degrees C/24 h); the variation rates of breakdown field and nonlinear coefficient are -0.3% and -6.7%, respectively. (C) 2009 Elsevier Ltd. All rights reserved.