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

Pengkang Xie,Kangning Wu,Ziyue Wang

doi:10.3390/ma15031098

Pengkang Xie, Kangning Wu + Show 1 more

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https://doi.org/10.3390/ma15031098

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Abstract

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 °C. Remarkable enhancement of the Schottky barrier height and electrical properties took place in the temperature range between 600 °C and 800 °C. The Bi-rich intergranular layer changed from β phase to α 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.

Highlights

Electronic ceramics with variable resistance on voltages are of importance in protecting electrical and electronic devices from overvoltage [1,2,3,4,5]
It has been acknowledged that the unique nonlinear current-voltage characteristics of ZnO based varistor ceramics originate from the double Schottky barriers (DSBs) at grain boundaries (GBs) [5,8], which further root in the underlying defect structures including the negatively charged interface sates and the positively charged intrinsic point defects in depletion layers [9]
ZnO varistor ceramic samples were quenched at different sintering stages to study the evolution of microstructures, electrical properties as well as Schottky barrier and its relating intrinsic and extrinsic point defects

Summary

Introduction

Electronic ceramics with variable resistance on voltages are of importance in protecting electrical and electronic devices from overvoltage [1,2,3,4,5]. The sintering process, especially the cooling process, is acknowledged to play important roles in the formation of DSBs at GBs [9,12,13,14]. Electrical properties of ZnO based varistor ceramics are largely dependent on the sintering temperature, atmosphere and cooling rates, which are further correlated with grain size distribution and height of DSBs at GBS. A number of studies about the sintering process mainly focused on the microstructural evolution, grain growth kinetics and phase formation of ZnO based ceramics [15,16,17,18,19].

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