Preparation of Composite Additives Powder by Coprecipitation Method and Investgation of ZnO Varistor Ceramics

ZnO varistor ceramic was prepared from composite additives powder synthesized by coprecipitation method. The coprecipitate precursor was investigated by thermogravimetric and differential thermal analysis. Phase formation, morphologies, component elements and particle size distribution of the obtained powder were characterized by X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope and dynamic laser scattering. Electrical properties of the prepared ZnO varistor ceramics were measured, then microstructure features of the ceramics were also observed. The results show that the mixture powder of each additive oxide is obtained by calcination of the precursor at 550 while the composite additives powder with pyrochlore-type composition of (Bi1.14Co0.26Mn0.29)(Sb1.14Cr0.57Ni0.29)O6.25 and average particle size of 0.26μm is achieved at 650 or 1 h. ZnO varistor ceramic prepared from the resulted composite additives powder exhibits a higher breakdown voltage (Eb=330 V/mm), a higher nonlinearity coefficient (α=47) and a lower leakage current (IL=5μA/cm2) than that prepared from conventional mixed oxide powder. The improvement in electrical properties is attributed to the more uniform microstructure.