Characterisation of Zn-3(VO4)(2) phases in V2O5-doped ZnO varistors

Zinc oxide-rich ZnO-V2O5 (ZV), ZnO-V2O5-MnO2 (ZVM) and ZnO-V2O5-Sb2O3 (ZVS) polycrystalliize ceramics have been prepared for detailed microstructural and electrical characterisation. All samples exhibit non-linear current-vol tage behaviour, with non-linear coefficients ranging from 5.0 for ZV to 16. 7 for ZVM. The use of X-ray powder diffraction together with microstructura l examination by transmission electron microscopy and a comparison of measu red interplanar spacings with those quoted in the literature for alpha-, be ta- and gamma-Zn-3(VO4)(2), has shown evidence for the formation of beta-Zn -3(VO4)(2) in ZV, gamma-Zn-3(VO4)(2) in ZVM and alpha-Zn-3(VO4)(2) in ZVS. The Zn-3(VO4)(2) phases are found to exist as smaller grains embedded in Zn O grains or residing at triple junctions. Electron diffraction suggests tha t beta-Zn-3(VO4)(2) has an orthorhombic A lattice, while gamma-Zn-3(VO4)(2) has a monoclinic C lattice. (C) 1999 Elsevier Science Limited. All rights reserved.