Microstructure, electrical properties, and aging behavior of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-Er2O3 varistor ceramics

The microstructure, electrical properties, and aging behavior of the ZnO-Pr6O11-CoO-Cr2O3-Y2O3-Er2O3 varistor ceramics were investigated for different contents of Er2O3. The microstructure consisted of ZnO grain and an intergranular layer (Pr, Y, and Er-rich phases) as a secondary phase. The increase of Er2O3 content decreased the average grain size and increased the sintered density. As the Er2O3 content increased, the breakdown field increased from 4206 V/cm to 5857 V/cm and the nonlinear coefficient increased from 32.6 to 48.6. The varistor ceramics added with 1.0 mol% Er2O3 exhibited excellent stability by exhibiting -0.2% in the variation rate of the breakdown field and -2.7% in the variation rate of the nonlinear coefficient for aging stress of 0.95 E-1 (mA)/150 degrees C/24 h. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.