Influence of Bi2O3/TiO2, Sb2O3 and Cr2O3 doping on low-voltage varistor ceramics

The influence of the amount of Bi2O3 and TiO2 additions at a TiO2/Bi2O3 ratio of 1, as well as Sb2O3 and/or Cr2O3 doping, on the microstructural development and electrical properties of varistor ceramics in the ZnO-Bi2O3-TiO2-Co3O4-Mn2O3 system was investigated In samples with a low level of Bi2O3 and TiO2 (0.3 mol%) and therefore small amount of liquid phase, exaggerated growth of the ZnO grains results in high microstructural inhomogeneity. Co-doping with Sb2O3 significantly changes the phase composition of TiO2 doped low-voltage varistor ceramics. The Bi3Zn2Sb3O11 type pyrochlore phase forms at the expense of the gamma-Bi2O3 and Bi4Ti3O12 phases and decreases the amount of liquid phase in the early stages of sintering. Already small amounts of Sb2O3 and/or Cr2O3 added to a TiO2 doped low-voltage varistor ceramics limit ZnO grain growth and increase the threshold voltage V-T Of the samples. (C) 1999 Elsevier Science Limited. All rights reserved.