| Abstrakt: |
The effect of sintering temperature on the microstructural evolution and electrical properties of ZnO-Bi2O3-Sb2O3-MnO2-Co2O3-Cr2O3-SiO2 varistors was studied in detail. With sintering at 900°C, polyhedral Bi-rich phase Bi3.73Sb0.27O6.0+x was distributed in the ZnO grain boundaries, preventing the effective formation of the double Schottky barrier. With an increase in the sintering temperature from 900°C to 1000°C, the liquefaction of Bi-rich phase occurred, leading to the beneficiation of Mn and Cr in the Bi-rich phase Bi3.73Sb0.27O6.0+x, and a lamellar Bi-rich phase formed in the ZnO grain boundaries during cooling. Excess O and enriched Mn4+ in Bi-rich phase Bi3.73Sb0.27O6.0+x serving as oxidizing agent acted as acceptors of e−, thus improving the double Schottky barrier. When the sintering temperature was further increased from 1000°C to 1100°C, the volatilization of the Bi-rich phase intensified, the thickness of the Bi-rich thin layers increased, and the uniformity decreased, leading to the deterioration of the microstructure and electrical properties of the ZnO varistors. Ion diffusion was stronger for the samples sintered at higher temperature, leading to more obvious polarization and loss peak. Finally, the ZnO varistors sintered at 1000°C for 2 h obtained a nonlinear coefficient of 43.4 ± 2.3, voltage gradient of 451 ± 4 V/mm, and leakage current density of 4.5 ± 0.4 μA/cm2 , demonstrating optimal microstructural uniformity and reproducibility of the sample preparation. The intensive study of sintering temperature has important relevance for the preparation of ZnO varistors with excellent microstructural uniformity and electrical properties. [ABSTRACT FROM AUTHOR] |
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