Preparation And Study Of Machanism Of Varistor Materials Doped With Rare-earths Oxide And Nano ZnO

Rare-earths oxide and nano ZnO were used as additives introducing to ZnO ceramics to improve its properties. The influence of nano ZnO on the electrical properties of varistor was studied, and the influence of Rare-earths oxide on the electrical properties of ZnO varistor was systems studied the first time.The effects of heating rate, sintering temperature, heat preserving time and cooling rate on the electrical properties of ZnO varistors was studied. The results show that it is an effective method for acquiring better electrical properties that the pressed bodies were sintered at 1150 in furnace with the temperature raised dilatorily, heat preserved for 2.5 hours and furnace cooled to room temperature.NdaO3, CeO2 and La2O3 were used as additives introduced to ZnO varistor materials. The influence of these additives on the electrical properties of ZnO varistor was studied, and the compositions of the additives were optimized. The results show that the effect of Nd2O3 on improving the varistor voltage is the most outstanding, the effect of La2O3 is more outstanding and that of CeO2 is the inferior. Adding 0.04mol% Nd2O3 improves the varistor voltage remarkably, and at the same time decreases the leakage current and the voltage ratio, then zinc oxide varistor showoutstanding comprehensively performance.Nano ZnO powder was added into varistor materials. The influence of nano ZnO on the electrical properties of varistor was studied, and the content of nano ZnO was optimized. The results show that nano ZnO improve the voltage of the varistor evidently. When the content of nano ZnO is 10wt%, the varistor voltage of ZnO varistor is higher, the voltage ratio is lower, and the leakage current is the lowest, which means better electrical properties of varistor.The microstruture of zinc oxide varistor with rare-earths oxide was studied by using scanning electronic microscope (SEM), energy spectrum apparatus (EPD), X-ray diffraction (XRD), and micrograph analysis system. It is suggested that rare-earths oxide Nd2O3> CeO2 and La2O3 reduce the grain size because the phases containing rare-earths element such as CeO2 and La2Os, which are independent phases, and the new phase Na2Nd2Sb2(Zn2AIOi2) containing neodymium all exist at the grain boundaries, hinder the movement of grain boundaries. Moreover, the additives (Nd2O3^ CeO2 and La2Oa) increase the concentration of free electron of zinc oxide crystal during sintering, then decrease the concentration of interstitial zinc, and finally hinder the growth of zinc oxide grain. Therefore, adding rare-earths oxides (Nd2Os> CeO2 and La2O3) with appropriate content decreases the size of ZnO grain evidently and makes the grain size and distribution more homogeneous, then the zinc oxide varistor show outstanding comprehensively performance.The microstruture of the varistor with nano ZnO was studied. The results show that nano additive reduces the size of ZnO grain, which leads to the evident improvement of the electrical properties of varistor.The quantitative theory of optimum doping content of electrical film materials was introduced, and an expression was obtained. Using this expression to calculate the optimum rare-earths oxides (Nd2O3, CeO2 andLa2O3) content of zinc oxide varistor, the quantitative calculation results are in accordance with the experimental results approximately.The double shottky potentical barrier was showed in form of catoon using Flash, from which we can comprehend the conduction theory of zinc oxide varistor. The electrical properties of varistor can be improved depend on it.