Influence of sintering temperature on electrical properties of ZnO varistors

The electrical properties of the ZnO varistors are demonstrated in this present study to be affected by the sintering temperature. The variation of the non-ohmic behavior with sintering temperature is indicated from I-V and C-V measurements to be a result of the changes of the interface defect density at the grain boundaries and the donor concentration in the ZnO grains. A shallow Schottky barrier is formed as a result of a low interface defect density, which is caused by losing the liquid-phase sintered materials, such as Bi2O3, when the metal oxide additives along the grain boundaries are sintered at a high temperature. The dielectric characteristic of the ZnO varistors is also affected by the sintering temperature. From the dielectric loss analysis and the complex-plane analysis it is found that there are two intrinsic defects, V0. and Zni.., within the ZnO varistors. The natures of these defects as a function of sintering temperature are also mentioned.