Effect of dopant valence state of Mn-ions on the microstructures and nonlinear properties of microwave sintered ZnO-V2O5 varistors

In this study, the effect of dopant valence state of Mn-species on the microstructure and conduction behavior of microwave sintered ZnO-V2O5 ceramics was analyzed. Microwave sintering can markedly enhance the densification rate of ZnO-V2O5 ceramics, regardless the valence state of Mn-species incorporated. But only the samples doped with low valences Mn-ions (Mn2+ or Mn2.66+) exhibit large nonlinear coefficient (alpha = 21.9) with low leakage current density, whereas the ZnO-V2O5 ceramics added with high valence Mn-ions (Mn4+) show inferior nonohmic behaviors with high leakage current density under the same sintering conditions. Restated, the valence state of Mn-species incorporated in ZnO-V2O5 ceramics, insignificantly alters the grain growth behavior but markedly modifies their nonlinear electrical properties. (C) 2003 Kluwer Academic Publishers.