Bi2O3與Sb2O3對ZnO變阻器的微結構及電性之影響
Effects of Bi2O3 and Sb2O3 on the microstructure and electrical properties of ZnO varistors
Date Issued
2006
Date
2006
Author(s)
Lao, Yeh-Wu
DOI
zh-TW
Abstract
The electrical properties of ZnO varistors depend strongly on their microstructure. In the present study, microstructural evolution of ZnO, Bi-doped ZnO and Bi,Sb-codoped ZnO during sintering is investigated. Emphasis is made on the factors to control the grain size distribution of ZnO grains.
Experimental results indicated that the vaporization of Bi2O3 is dramatical above 800℃. A powder bed with the same composition as that of the specimens can significantly reduce the vaporization. A transient liquid phase is present in the Bi2O3-doped ZnO systems as no powder bed is used. Such transient liquid phase enhances the densification and grain growth as its amount is higher than a critical value. After sintering, no residual liquid phase is found. The segregation of Bi3+ ion is evidenced by the change of dihedral anagle and electrical properties. The segregation has little effect on the grain size distribution of ZnO grains.
Zn7Sb2O12 spinel and inversion boundaries (IBs) are found in the Bi,Sb-codoped ZnO specimens when they are sintered without a powder bed. The presence of the spinel and IBs reduces the grain size and its distribution.
By using a powder bed, a Bi-rich phase is existed in the Bi-doped ZnO specimens. The presence of the Bi-rich liquid phase enhances significantly the size of ZnO grains. In the Bi,Sb-codoped ZnO specimens, apart from the Bi-rich liquid phase, both pyrochlore and spinel are formed after sintering. The presence of the pyrochlore is detrimental to the electrical properties.
Both the Bi-segregation and Bi-rich liquid phase could provide an electrostatic barrier at grain goundaries and result in a nonlinear I-V characteristic. In the present study, based on the microstructure analysis, a methodology to calculate the breakdown voltage per grain boundary (Vgb) is proposed.
Subjects
氧化鋅
氧化鉍
氧化銻
變阻器
晶粒大小分佈
液相燒結
微結構
電性
ZnO
Bi2O3
Sb2O3
Varistor
Grain size distribution
Liquid phase sintering
Microstructure
Electrical property
Type
thesis
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