Evolution of Intrinsic and Extrinsic Electron Traps at Grain Boundary during Sintering ZnO Based Varistor Ceramics

In this paper, evolution of microstructures, electrical properties and defects of the double Schottky barrier during the sintering process were investigated by quenching ZnO varistor ceramics at different sintering stages. It was found that morphology of the samples changed little when the temperature was below 800 degrees C. Remarkable enhancement of the Schottky barrier height and electrical properties took place in the temperature range between 600 degrees C and 800 degrees C. The Bi-rich intergranular layer changed from beta phase to alpha phase. The interfacial relaxation at depletion/intergranular layers became detectable in the samples. Meanwhile, a distinct relaxation loss peak from electron trapping of interface states was observed instead of two dispersed ones. It indicated that the differences among the Schottky barriers in ZnO varistor ceramics became smaller with the process of sintering, which was also supported by the admittance spectra. In addition, oxygen vacancy was found more sensitive to the sintering process than zinc interstitial. The results could provide guidance for fine manipulating the Schottky barrier and its underlying defect structures by optimizing sintering process.

Automated summary

This paper investigates the evolution of the double Schottky barrier during the sintering process and finds that the morphology of the samples changes little below 800 degrees C. Significant enhancement of the Schottky barrier height and electrical properties occurs in the temperature range between 600 degrees C and 800 degrees C. Oxygen vacancy is found to be more sensitive to the sintering process than zinc interstitial.