Effect of MnCO3 on ZnO-Pr6O11-Co2O3-Cr2O3 Varistor Ceramics

0~1.5mol% MnCO3doped ZnO-Pr6O11-Co2O3-Cr2O3varistor ceramics were synthesized by conventional oxides mixing procedure. The effect of MnCO3variations on the microstructure, phase constituents and electric field–current density (E-J) characteristics of the ceramics were studied by SEM, XRD examinations and standard E-J test. The result showed the electrical nonlinearity exponents and breakdown voltage of the ceramics increased from 38 and 1296V/mm of the un-doped one to 52 and 1420V/mm respectively with the addition of 0.5mol% MnCO3; meanwhile, the leak current density was reduced from 4.35μA/cm2 to 2.05 μA/cm2. Further doping MnCO3deteriorated the overall varistor properties of the ceramics by remarkably decreasing the density of the ceramic, and the main reason causing the density drop was ascribed to the hindering effect of the well dispersed perovskite-like Pr0.95Mn0.9393O3particles formed mainly within the ZnO grain boundary areas.