Y 2 O 3 doping on the electrical properties of ZnO varistor ceramics impact
Pang Chi a fee pride 2
(1 Materials Science and Engineering, Guizhou University, Guizhou, Fei Ge 2 Electronics Co., Ltd.)
Abstract: In this paper, the traditional ceramic technology, comparative study of different Y 2 O 3 content on the ZnO varistor performance. The results showed that: doped Y 2 O 3 grains can be refined to improve ZnO varistor voltage gradient, when the doping amount of 0.8%, the potential gradient over 270V/mm, but the low sample density, electrical properties decline. When the Y 2 O 3 content of 0.lWt.%, The potential gradient with non-doped Y 2 O 3 sample rather, its high density, grain size consistent, the best electrical properties.
Key words: ZnO varistor; Y 2 O 3-doping; voltage gradient
1. Foreword
ZnO varistors due to the high gradient film can reduce the height of surge arresters, reduce its volume, reducing its weight, so high pressure, special high-voltage surge arresters and surge arresters and other line-type ZnO varistors for high-gradient film growing demand research in this area is very impressive, has achieved some results [1]. Improve the potential gradient methods are more, such as the use of lower sintering temperature, reduce holding time and other low-temperature sintering technology; adopt a more fine materials such as nano-materials and so on can be reduced when the grain size; used to suppress ZnO doped with rare earth oxide crystal grain growth, thereby enhancing the potential gradient. Some of these methods, however the production cost is too high, and some methods to improve the gradient at the same time, electrical properties tend to decrease, limiting high gradient of pressure-sensitive resistor pressure-sensitive industry in China's industrialization.
In this paper, ZnO-Bi 2 O 3 Department of varistor ceramics doped with different content of Y 2 O 3, test its electrical properties, and its role in the mechanism of a preliminary study, in order to explore the Y 2 O 3-doped ZnO as the increase varistors provide the potential gradient of practical value for reference.
2. Experiment
The ZnO powder and Bi 2 O 3, Co 3 O 4, MnO 2, Sb 2 O 3, Cr 2 O 3 and other additives according to formula (mole fraction): 97% ZnO +1% Bi 2 O 3 +0.5% Co 3 O 4 +0.5% Sb 2 O 3 +0.5% MnO 2 +0.5% Cr 2 O 3 and accurately weighed, were added to the weight ratio of 0,0.05%, 0.1%, 0.2%, 0.4% and 0.8% of the Y 2 O 3, with the wet ball milling 24h, after sifting through the drying by adding an appropriate amount of the concentration of 5% of PVA aqueous solution as adhesive, dry-pressed into a side length of 40 ¡Á 40mm, thickness 4.4mm, density 3.2g / cm 3 of the Green, slow heating to 350 ¡æ after row of plastic, and then heated to 1120 ¡æ, heat 2h after cooling down to room temperature with the furnace at 650 ¡æ annealing, burning seepage silver electrode, obtained samples were denoted by Y 0, Y 1, Y 2, Y 3, Y 4, Y 5.
By CJ1001 Varistor samples measured DC parameters of varistor voltage, leakage current, non-linear coefficient, with the FGL-40-based test-bed testing the impact of lightning current 8/20ms high current characteristics, with the JJW-2000VA AC Precision cleaning regulated power supply, FGT-TOV-based test-bed testing TOV aging properties, with the JSM-6360LV scanning electron microscope analysis of the sample microstructure.
3. Results and discussion
Figure .1 is the amount of yttria-doped varistor ceramics with relative density relationship, Table .1 is the right amount of yttria-doped varistor low current characteristics. Figure .1 and Table .1 can be seen, with the Y 2 O 3 content increasing, the sample density decreased gradually. Y 2 O 3 content from 0 to 0.8%, the relative density (sample density and theoretical density ratio) from 98.5%, fell 93.3 percent. When the Y 2 O 3 doping content of 0.1%, the potential gradient there signs of reduction, with non-doped Y 2 O 3 of the Y 0 sample potential gradient rather, this is consistent with Yu-Ping Wang and others studies [2], than this inflection point, a potential gradient and the amount of basic with the increase in doping gradually increased. When the doping amount of 0.8%, the potential gradient reaches its maximum 270V/mm.
Fig .1 yttrium oxide varistor ceramics doped with volume and the relationship between the relative density of
Table .1 yttria doping on the varistor characteristics of small current
|
Sample |
Y 0 |
Y 1 |
Y 2 |
Y 3 |
Y 4 |
Y 5 |
|
Varistor voltage (V) |
620 |
694 |
640 |
767 |
910 |
985 |
|
Voltage gradient (V / mm) |
170 |
190 |
175 |
210 |
250 |
270 |
|
I L (¦ÌA) |
4.2 |
2.9 |
3.3 |
4.1 |
2.5 |
2.2 |
Fig .2, Figure .3, respectively 8/20¦Ìs results and the impact of lightning current characteristics of varistor TOV test results. .2 Can be seen from the diagram, with the Y 2 O 3 content increased, the sample 8/20¦Ìs lightning ability to significantly improve the circulation flow in the Y 2 O 3 content of 0.1%, the maximum value, Y 2 O 3 content of a further increase, 8/20¦Ìs lightning streaming capability in circulation decreased. .3 Can be seen from the diagram in the Y 2 O 3 content of 0.1%, the maximum thermal tripping current, is about 1200mA, than non-doped Y 2 O 3 samples increased three-fold, and as Y 2 O 3 content further increases, the drop in the thermal trip.
Fig .2 8/20¦Ìs lightning current 20KA hit 30 times after the varistor voltage change rate
Fig .3 yttria doping on the characteristics of varistor TOV
Fig .4 different Y 2 O 3 content of the SEM photographs varistor
Y 0, Y 2, Y 5 3 SEM photographs of samples as shown in Figure .4, with the Y 2 O 3 doping content increases, ZnO grain size gradually decreases, indicating the Y 2 O 3 to join can indeed play a role in grain refinement [3]. Author believes that: Y 2 O 3 at grain boundaries or grain junctions, or the solution in other intergranular phase, which phase to become a small pinning centers, thus inhibiting grain growth is leading to a potential gradient of l high. Y 2 samples, however, a potential gradient anomalies occur, the authors considered the Schottky barrier height reduction and grain boundaries increase in the number two in the result of both, but lower Schottky barrier height played a major role, this also the need for further in-depth study.
In the ZnO grain size gradually decreases at the same time, the sample density decreased gradually. This is because the grain growth, grain boundary movement, at the same time led to grain boundary movement of stomata, small pores grew up in the merger discharged from the ceramic body, thus completing the process of ceramic sintering. As the Y 2 O 3 grains to join inhibit the full development, stomata can not be discharged, resulting in an increase in porosity, the sample density decreased. Y 0 sample, the undoped Y 2 O 3, appeared abnormal grain grew up in large reduction in grain at the grain boundary, leading to resistance is lowered, the current focus on here, which occurs easily in the electrical breakdown, so its 8/20¦Ìs lightning circulation flow capacity, thermal tripping right and wrong. The sample Y 2 grain, although not the smallest, not the highest density, but its grain growth in line, so the high-current characteristics of the best. Y 2 O 3 with the further increase, Y 5 samples the relative density of only 93.3%, ceramic body There are a lot of pores, which will inevitably lead to deterioration of its electrical properties.
4. Conclusion
(1) Y 2 O 3-doping can refine grain, increasing the potential ZnO Varistor gradient, in the doping amount of 0.8%, the potential gradient over 270V/mm.
(2) With the amount of Y 2 O 3 doping increases, the sample density decreased gradually, which leads to deterioration of electrical properties of varistors.
(3) When the doping amount of 0.l Wt.%, The potential gradient with non-doped Y 2 O 3 sample rather, its high density, grain size consistent, the best electrical properties.
References
[1] Yu-Ping Wang, Li Sheng-tao. New type of ZnO Varistors Research progress [J]. Electrical Applications, 2005 (6): 1 ~ 8.
[2] Yu-Ping Wang, Ma. Doped Y 2 O 3 in ZnO-Bi 2 O 3-Sb 2 O 2 system varistor [A]. China Institute of Electronics Technology Branch of the thirteenth session of the voltage-sensitive Min Annual Conference Papers [C] 2006:70 ~ 75.
[3] Yu-Ping Wang, Ma. Y 2 O 3-doped zinc oxide varistor ceramics microstructure and electrical properties [J]. Piezoelectric and acousto-optic, 2007,29 (6): 114 ~ 119.
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