Therefore,, which is reported elsewhere. The absence of a spinel phase increases the active grain boundary area through which the electrical current flows. On the other hand, Pr 6 O 11 -based ZnO varistors are reported to have only two-phases detected by X-ray diffraction, namely, ZnO grains and intergranular layers enriched with praseo- dymium 13. To overcome the problems in Bi 2 O 3 -based varistors, ZnO varistors using praseodymium oxides as VFO have been reported. ZnO varistors generally contain three phases, such as ZnO grains, Bi 2 O 3 -rich intergranular layer and spinel particles 10. Another flaw of Bi 2 O 3 -based varistors is that they need many additives to obtain high nonlinearity and stable electrical properties. Although they exhibit excellent varistor performance, they possess few drawbacks due to the high volatility and reactivity of Bi 2 O 3 at a sintering temperature above 1000 ☌ 10. Most of commercial ZnO varistors are ZnO-Bi 2 O 3 -based varistor ceramics, possessing as major additive Bi 2 O 3.
![download film runaway al ghazali download film runaway al ghazali](https://4.bp.blogspot.com/-SH9Zf_fXOwY/U88X0GtRzsI/AAAAAAAAc5A/KKtlOfrBzVo/s1600/Run+Away.jpg)
However, the Pr 6 O 11 -based ZnO varistors don't have volatilization of compo- nents 3 and they own a simpler microstructure when compared with Bi 2 O 3 -based varistors, which is an important fact for the stability and degradation phenomena. In fact, the history of Pr 6 O 11 -based ZnO varistors is similar to the Bi 2 O 3 -based ZnO varistors 5, but they have not been adequately studied.
![download film runaway al ghazali download film runaway al ghazali](https://2.bp.blogspot.com/-PNZGesY4gBM/U88YFqd10XI/AAAAAAAAc5g/eXq_75Gkego/s1600/Run-Away-Wajah-Al-Ghazali-dipukul-di-film-Runaway.png)
Zinc oxide ceramics, containing Pr 6 O 11 and CoO, which exhibit current nonohmic characteristics, were first reported by Mukae et al.
![download film runaway al ghazali download film runaway al ghazali](https://1.bp.blogspot.com/-LhEFVpkIbuw/XvCHJNJwFhI/AAAAAAAAX7g/_UwEOqByw78q7WRciXnSPvkLas5MLoxuQCLcBGAsYHQ/w1200-h630-p-k-no-nu/Custom%2Bdimensions%2B640x426%2Bpx%2B%25282%2529.jpeg)
The second class of additives are 3d transition-metal oxides, which improve significantly the nonohmic characteristics 3. The first class of such additives are varistor-forming oxides (VFO), such as Bi 2 O 3, Pr 6 O 11, La 2 O 3, BaO, V 2 O 5 and glass frits. It has been recognized that at least two different classes of additives must be added to the ceramic varistors in order to obtain good nonohmic characteristics 2. varistor ceramics are resistor devices manufactured by sintering ZnO powder containing various minor additives 1.