ZnO varistors prepared by direct mixing of constituent phases

Abstract

ZnO varistors with non-linearity coefficients reaching 50 and low values of the leakage current (approximately 0.01 A/m2), were obtained by a method referred to as `direct mixing of constituent phases'. The method is based on sintering of a mixture of the constituent phases with the following compositions: ZnO phase uniformly doped with Co2+ and Mn2+; intergranular phase: γ-Bi2O3 stabilized with Mn2+ or Zn2+; spinel phase: Zn1.971Ni0.090Co0.030Cr0.247Mn0.090Sb0.545O4. As proved, the obtained varistors are composed of the same phases as those introduced into the system. The influence of composition as well as milling and sintering parameters on the varistor characteristics were investigated. Some varistor powder mixtures were intensively milled before sintering. As a result, high density ceramics with highly homogeneous microstructure were obtained after sintering.