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 Zn(i), within the ZnO varistors. The natures of these defects as a function of sintering temperature are also mentioned.