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      Influence of processing on microstructure and electrical characteristics of multilayer varistors


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          The paper reports on the influence of processing on microstructure and electrical properties of multilayer varistors based on zinc oxide doped with Bi 2O 3, Sb 2O 3, Co 2O 3, MnO, Cr 2O 3, B 2O 3, and SiO 2. 0.5–1 wt% of AlF 3–CaB 4O 7 was used as a new effective sintering aid. The behavior of green laminates during heating was characterized using differential thermal analysis and a heating microscope. As revealed by XRD, SEM, and EDS methods, the varistor layers are composed of ZnO grains of 1–5 μm size, submicrometer spinel and pyrochlore grains situated at the ZnO grain boundaries, and nanometric Bi 2O 3-rich films surrounding ZnO grains. Complex impedance studies carried out in the frequency range of 0.01 Hz–2 MHz at temperatures changing from −30 to 150 °C imply the formation of semiconducting grains and insulating grain boundaries. Frequency dependence of dielectric permittivity shows a high plateau at lower frequencies, typical for barrier layer capacitance effect. The fabricated multilayer varistors show nonlinear current–voltage characteristics with a high nonlinear coefficient of 26–38. The breakdown voltage was found to decrease within the range of 66–130 V with sintering temperature increasing from 1000 to 1100 °C. Good surge current capability of the varistors was confirmed by the tests using 8/20 μs pulses.

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          Author and article information

          J Adv Ceram
          Journal of Advanced Ceramics
          Tsinghua University Press and Springer-Verlag Berlin Heidelberg (USA )
          01 September 2019
          01 October 2019
          : 8
          : 3
          : 408-417
          1Institute of Electron Technology, Kraków Division, Zabłocie 39, 30-701 Kraków, Poland
          Author notes
          *Corresponding author: D. SZWAGIERCZAK, E-mail: dszwagi@ 123456ite.waw.pl
          Copyright © The Author(s)

          This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. See https://creativecommons.org/licenses/by/4.0/.

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