Influence of pre-synthetic spinels on electrical properties of ZnO varistors

A method of preparation of ZnO varistors, presynthetic spinels, was explored and its influence on electrical properties was examined. Microstructural features and distribution characteristics of the spinel phase in ZnO varistors were also investigated by electron probe microanalysis and TEM (transmission electron microscopy). The electrical properties of two types of samples are compared and discussed in relation to the spinel characteristics. The procedure of presynthetic spinels results in a drop of breakdown voltage of about 50%, a one-order decrease of leakage current, and a significant improvement of thermal stability. The I-V characteristics of ZnO varistors are influenced not only by the Bi₂O₃ intergranular phase, but also by the distribution characteristics of the spinel phases, which can be modified considerably by varying the technological procedure