Influence of alkali ions in enhancing the nonlinearity of ZnO-Bi2O3-Co3O4 varistor ceramics

被引:29
作者
Kutty, TRN
Ezhilvalavan, S
机构
[1] Materials Research Centre, Indian Institute of Science, Bangalore
来源
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS | 1995年 / 34卷 / 11期
关键词
ZnO varistor; alkali ions; transition metals; oxidation state;
D O I
10.1143/JJAP.34.6125
中图分类号
O59 [应用物理学];
学科分类号
摘要
Zinc oxide ceramic varistors with simplified compositions of ZnO+Bi2O3+Co3O4+M(2)O (M=K or Na) show nonlinearity coefficients (alpha) of 40-75. The electron paramagnetic resonance spectra and optical reflectance spectra show that there is a direct interdependence between the oxidation state of transition metals and the alkali ions. The X-ray photoelectron spectra indicate that the alkali ions preserve a higher oxidation state of cobalt, Co(III), in the grain boundary regions than in the grain interiors having more Co(II). Admittance spectroscopy shows that, while the nature of traps remains unaltered, the trap density increases with the concentration of alkali ions near the interface. The observed defect states are associated with the grain bulk than with the grain boundary interfaces, as indicated by the isothermal capacitance transient signals.
引用
收藏
页码:6125 / 6132
页数:8
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