PREPARATION AND CHARACTERIZATION OF NANOCRYSTALLINE ZNO BASED MATERIALS FOR VARISTOR APPLICATIONS

Ultra fine zinc oxide powders with the size of crystallites In the ran ge between. 3 and 10 nm have been prepared by colloidal suspension and centrifugal separation method. The powders were characterized by DTA and XRD. The average crystallite size was estimated from the XRD profi le width, using Scherrer equation. The crystallite sizes remained in n m scale on heat treatment upto 750 degrees C. Different valence state elements (Go, Sb, B, Bi, Sn & Cu) in oxide form were additively doped with ZnO by dissolution. process for fabrication of varistors. These a dditives form a continuous thin. layer over the conducting ZnO crystal lite surfaces and make the boundary or interface regions insulating. N on-linear exponent, alpha, of approximate to 50 and normalized breakdo wn voltage approximate to 30 kV cm(-1) were obtained for the varistors made of nanostructured ZnO.