Effect of Mn on the ZnBiMnO varistor ceramics sintered at a low-temperature of 875 °C

The effect of Mn on ZnO-Bi2O3 (ZnBiO) based varistor ceramics sintered below 900 degrees C has not been fully understood due to the conventional ZnBiO-based varistor ceramics usually being sintered at temperatures higher than 900 degrees C. Therefore, (99.5-x) ZnO+0.5Bi2O3+xMnCO3 (x = 0, 1, 2, and 3; all in mole ratio) ceramics were prepared by solid-state sintering at 875 degrees C for 3 h to study the effect of Mn on the microstructure, electrical nonlinear properties and their stability within the range of 25-100 degrees C. The results show that doping MnCO3 results in the formation of Mn3O4 and Bi12MnO20 secondary phases within the sintered samples. Mn3O4 mainly exists at grain boundary as particle phase, restricting the growth of ZnO grains during sintering. The presence of Bi12MnO20 indicates MnCO3 may enhance the sintering of ZnBiMnO ceramics by increasing the amount of Bi-rich liquid phase. MnCO3 effectively improves the electrical nonlinear properties of ZnBiMnO varistor ceramic and their stability against the variations in ambient temperature. The 2 mol% MnCO3 doped ZnBiMnO varistor ceramic shows the best electrical nonlinearity, with a nonlinear coefficient, a breakdown voltage and a leakage current density of 53.61, 503.11 V/mm, and 2.85 mu A/cm2 respectively. This study may improve our understanding of the effect of Mn on the low-temperature sintered ZnBiO based varistor ceramics, and provide a promising candidate material for manufacturing low-cost ZnO based varistor.