Microwave Sintering of a Nanostructured Low-Level Additive ZnO-based Varistor

A simple and promising varistor with low additive level was obtained by rapid microwave sintering. In the present work, only 2%-mol of oxides, equimolarly distributed between Bi2O3, Sb2O3 and nanostructured Mn3O4 and CuO was added to nanostructured ZnO. The densification behavior, microstructure and phase development, as well as the electrical properties, were evaluated. Samples that were microwave-sintered at 950 degrees C for only 10 min showed a fine microstructure with average grain size of 2.27 mu m with approximately 94% of theoretical density, presenting the best electrical properties: high electrical field of approximately 15 kV/cm, non-linear coefficient of 40 and low leakage current (58 mu A). Besides the fine and homogeneous microstructure, the well-developed Schottky barrier can also be attributed to the role of copper. The contribution of the electrical and magnetic fields to densification and grain growth was explored.