Microstructure and nonlinear properties of microwave-sintered ZnO-V2O5 varistors: II, effect of Mn3O4 doping

Abstract

The microstructure and nonlinear current-voltage characteristics of Mn3O4-doped ZnO-V2O5 ceramics, microwave-sintered at 800 degrees-1200 degrees C for 10 min, have been investigated. A high density (96% of the theoretical density) has been achieved. The incorporation of Mn3O4 additives does not significantly alter the densification behavior of the ZnO-V2O5 materials, but rather pronouncedly increases the non-linear coefficient (alpha = 23.5) and markedly suppresses their leakage current density (J(L) = 2.4 x 10(-6) A/cm(2)). On the other hand, the intrinsic properties of the materials, including the Schottky barrier height (Phi(b)) and the donor density (N-d), are only moderately modified; that is, Phi(b) = 1.16 eV and N-d = 5.4 x 10(17)/cm(3). X-ray diffractometry analyses and energy-dispersive X-ray microanalyses (via scanning electron microscopy) indicate that the V2O5 species facilitate the densification and the development of microstructure via the formation of a liquid phase (Zn-3(VO4)(2)) along the grain boundaries, whereas the Mn3O4 species markedly enhance the nonohmic behavior of the ZnO-V2O5 materials by forming the surface states along the grain boundaries.