Ball milled ZnO for varistor applications.

In this paper, the characteristics of commercially available ZnO varistor materials are reviewed. The composition and microstructure have been investigated by scanning electron microscopy and the particle size distributions have been established. I-V characteristics have been measured on cross sections using the standard four-points technique. Nanocrystalline ZnO materials prepared by ball milling under various milling conditions have also been investigated. X-ray diffraction and electron microscopy have been used for structural investigation as a function of milling time. ZnO pellets were prepared by uniaxial pressing and sintered in air at 1250 degrees C. Preliminary I-V characteristics are reported. Studies are in progress in order to evaluate the conduction mechanisms and investigate the influence of grain size and structural defects on the IV characteristics.