Varistor behavior of Mn doped ZnO ceramics prepared from nanosized precursors

Polycrystalline ZnO doped with MnO, from 2 to 15 mol%, was prepared from nanosized precursors. The effect of Mn doping and sintering temperature on phase evolution, microstructure and V-I characteristics were investigated. SEM images showed that the great merit of using nanoparticles is that the samples with high microstructural uniformity and lower grain size can be achieved. Varistor behavior was observed in all specimens, even in the undoped ceramics due to the oxidation process of zinc interstitial defects at grain boundaries. The electric field versus current density (E-J) curves indicated that the breakdown field E-b increased and the nonlinear coefficient alpha decreased with the increase in doping level. 2 mol% Mn doped ceramic sintered at 1100 A degrees C exhibited the highest nonlinear coefficient, alpha = 40. The stability test under DC stress was performed for the undoped ZnO ceramics. ZnO varistor sintered at 1300 A degrees C showed not only high nonlinearity, but also high stability under DC stress.