Papers by Author: Yu Shi

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Authors: Ming Zhao, Meng Zhang, Yu Shi, Zhi Long Wang
Abstract: 0~1.5mol% MnCO3 doped ZnO-Pr6O11-Co2O3-Cr2O3 varistor ceramics were synthesized by conventional oxides mixing procedure. The effect of MnCO3 variations on the microstructure, phase constituents and electric field–current density (E-J) characteristics of the ceramics were studied by SEM, XRD examinations and standard E-J test. The result showed the electrical nonlinearity exponents and breakdown voltage of the ceramics increased from 38 and 1296V/mm of the un-doped one to 52 and 1420V/mm respectively with the addition of 0.5mol% MnCO3; meanwhile, the leak current density was reduced from 4.35μA/cm2 to 2.05 μA/cm2. Further doping MnCO3 deteriorated the overall varistor properties of the ceramics by remarkably decreasing the density of the ceramic, and the main reason causing the density drop was ascribed to the hindering effect of the well dispersed perovskite-like Pr0.95Mn0.9393O3 particles formed mainly within the ZnO grain boundary areas.
Authors: Xiao Xing Han, Si Chao Huang, Ying Liang, Yu Shi
Abstract: The effect of 0~1mol% MnO2 doping on microstructure and electrical properties of the Zn–Pr–Co–Cr–Mn-based varistor ceramics was investigated by means of SEM, XRD and standard current-voltage property tests. The increase of MnO2 doping level strongly decreased the relative density (99%-91.5%) by the effect of pining of Pr0.96Mn0.98 2O3. The nonlinear coefficient increased from 17.4 for MnO2-undoped sample to 54 for MnO2-doped sample up to 0.5 mol%, whereas the further doping resulted in decrease.
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