Microstructure and current-voltage characteristics of praseodymium-doped zinc oxide varistors containing MnO$\_2$, Sb$\_2$O$\_3$ and Co$\_3$O$\_4$

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• 作者：Hng ; H. H. ; Knowles ; K. M.
• 刊名：Journal of Materials Science
• 出版时间：2002
• 出版年：2002
• 期刊代码：24_00222461
• 类别：mat
• 卷：37
• 期：6
• 页码：1143-1154
• 数据来源：sp

摘要

The effects of the oxide additives MnO$\_2$, Sb$\_2$O$\_3$ and Co$\_3$O$\_4$ commonly incorporated in commercial Bi$\_2$O$\_3$-doped ZnO varistors on the microstructure and the current-voltage characteristics of 0.5 mol% Pr$\_6$O$\_11$-doped ZnO varistors have been studied. A 1 mol% addition of Co$\_3$O$\_4$ to the ZnO-Pr$\_6$O$\_11$ binary system does not produce any additional secondary phases in addition to Pr oxides. In contrast to this, the addition of 1 mol% MnO$\_2$ complicates the simple two-phase microstructure of the 0.5 mol% Pr$\_6$O$\_11$-doped material by forming the perovskite-type structure Pr(Mn$\_1\; -\; x$Zn$\_x$)O$\_3$. The addition of Sb$\_2$O$\_3$ produces the pyrochlore Pr$\_3$Zn$\_2$Sb$\_3$O$\_14$ and spinel Zn$\_7$Sb$\_2$O$\_12$ phases. Application of the Fresnel fringe technique and the diffuse dark field technique showed that there was an amorphous Pr-rich layer of thickness <2 nm residing between adjacent ZnO grains in all the samples studied.