Authors: Lan Yi Wang, Cheng Xiang Lu, Guo Yi Tang
Abstract: Two types of multilayer ZnO varistors are prepared by the chemically synthesized (CS) powder
and the mixed oxide (MO) powder. The ceramic microstructure analysis shows that the multilayer variestor
(MLV) ceramic prepared by the CS powder has the fine grain, the homogeneous distribution of grain
size and the uniform dopant distribution. The CS powder prepared multilayer ZnO varistors display better
electrical properties, including higher nonlinear coefficient, higher breakdown voltage, higher peak
current, lower leakage current and lower clamping voltage, than those made by the mixed oxide powder.
All these superior electrical properties are attributed to the CS powder, which makes more uniform dopant
distribution throughout the multilayer ZnO varistors. The homogeneous distribution for the various
dopants in the varistor ceramic has been achieved by the chemically synthesized doped ZnO powder.
Therefore, the chemically synthesized powder can be used in the manufacture of high performance
multilayer ZnO varistors.
739
Authors: Sasiporn Prasertpalichat, Muangjai Unruan, J. Tungsritrakul, Rattikorn Yimnirun
Abstract: It is well known that acceptor and donor doping results in opposite ferroelectric aging effects; however, the aging effects in hybrid-doped (acceptor+donor) has remained unclear. Thus, the aging effect of dielectric and ferroelectric properties in Fe3+/Nb5+ hybrid-doped BaTiO3 ceramics was investigated in this research. The concentration of acceptor dopant (Fe3+) was fixed at 1 mol% while that of donor dopant (Nb5+) was varied from 0.5-2.0 mol%. XRD technique was used to study the phase morphology. Before measuring dielectric and ferroelectric aging effect, all samples were deaged at 250 °C for 1 hour. The results showed that the dielectric properties of all deaged samples have decreased exponentially with time. The deaged samples with 0.5 and 1.0 mol% of Nb5+ obviously showed double hysteresis loop while that with higher concentration of Nb5+ (1.5-2.0 mol%) showed the rectangular (normal) hysteresis loop. The explanations based on the effect of defect dipole were discussed.
233
Authors: Jun Hu, Wang Chen Long, Jin Liang He, Jun Liu, Feng Chao Luo
Abstract: The additive of Al(NO3)3 has been doped into ZnO varistors in order to reduce their residual voltages. However, the leakage currents of samples always increase at the same time. Generally, it is recognized that some of doped Al3+ ions enter the ZnO grains and reduce their resistivity, which results in lower residual voltages of varistor samples. On the other hand, the remnant Al3+ ions appear in the grain boundaries and also reduce their resistivity, which results in larger leakage currents. In this paper, the electrical properties of ZnO varistor samples with various amounts of Al(NO3)3 dopant were measured. The experimental data are compared with the numerical simulation results, which reveals that the increased leakage currents of ZnO varistors with Al(NO3)3 dopant are not only due to the decreased resistivity of grain boundaries, but also the increased donor density of ZnO grains.
386
Authors: Sen Wang, Zhi Hui Li, Xin Liu, Huan Zhang
Abstract: Anti–reducing effect of CaO in barium titanate based ceramic materials sintered at reducing atmosphere and the structure development of the materials has been studied in this paper.The results show: Addition of CaO in barium titanate based ceramic will keep resistivity of the sample sintered at reducing atmosphere at a high level. The resistivity of the materials increase with the increasing of CaO, and the resistivity keep in constant after the amount of CaO excess 3mol%. In the sample with sintering aid of SiO2 and BaO-excess, introducing of CaO may improve the resistivity of the materials obviously. A slight new phase formation was found in the BaO-excess sample, but no new phase formation was found in the non BaO-excess sample. If there is sintering aid of SiO2 in the sample, CaO may accelerate liquid phase film formation at the surface of grains, which will suppress the diffusion of oxygen in the grains to the environment.
2457
Authors: Mohammad Amerul Azree Jamil, Johar Banjuraizah, Shing Fhan Khor, Zainal Arifin Ahmad
Abstract: PZT ceramic is synthesis by using sol gel method.Introducing a dopant to the pure PZT can help to enhance the properties of the piezoelectric ceramic. The effects of sintering temperature on phase formation, densification of the ceramics have been investigated using XRD, SEM and Archimedes method. The bulk density and porosity of PZT decreased as the sintering temperature increased.
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