Materials Research (Dec 2005)

Microstructural evaluation of rare-earth-zinc oxide-based varistor ceramics

  • José Geraldo de Melo Furtado,
  • Luiz Antônio Saléh,
  • Eduardo Torres Serra,
  • Glória Suzana Gomes de Oliveira,
  • Maria Cecília de Souza Nóbrega

DOI
https://doi.org/10.1590/S1516-14392005000400011
Journal volume & issue
Vol. 8, no. 4
pp. 425 – 429

Abstract

Read online

Zinc oxide varistors are nonlinear voltage dependent ceramic resistors used to suppress and limit transient voltage surges. The work reported in this paper involves the relationship between microstructural characteristics and the varistor performance of ZnO ceramics doped with rare-earth oxides. Samples of these ceramics with different nonlinear current-voltage characteristics, according to the specific chemical composition and sintering parameters, were prepared and microstructurally analyzed by scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray fluorescence spectroscopy and X-ray diffraction. The results denote that intergranular phase is rich in rare-earth elements, but its morphology, obtained by selective leaching of ZnO grains (which are only doped with Co), provides evidence that ZnO grains are not completely surrounding by the intergranular phase, also existing ZnO grains are in direct contact with each other, as well as it occurs in conventional varistor system.

Keywords